Home gtgt Inventory-Buchhaltung-Themen Moving Average Inventory-Methode Gleitender Durchschnitt Inventory Method Overview Unter der gleitenden Average Inventory-Methode werden die durchschnittlichen Kosten für jedes Inventar Item im Bestand nach jedem Inventarkauf neu berechnet. Dieses Verfahren tendiert dazu, Inventarwerte und die Kosten der verkauften Waren zu erbringen, die zwischen denjenigen liegen, die unter der ersten In-First-Out-Methode (FIFO-Methode) und der LIFO-Methode (LIFO-Methode) abgewickelt werden. Dieser Mittelungsansatz wird als ein sicherer und konservativer Ansatz für die Berichterstattung der finanziellen Ergebnisse betrachtet. Die Berechnung ist die Gesamtkosten der gekauften Artikel geteilt durch die Anzahl der Artikel auf Lager. Die Kosten für die Beendigung des Inventars und die Kosten der verkauften Waren sind dann auf diese Durchschnittskosten festgelegt. Es werden keine Kostenschichten benötigt, wie es für die FIFO - und LIFO-Methoden erforderlich ist. Da sich die gleitenden Durchschnittskosten bei jedem Neukauf ändern, kann die Methode nur mit einem Perpetual-Inventory-Tracking-System verwendet werden, so dass ein solches System die aktuellen Bestände der Bestände aufrechterhält. Sie können die gleitende durchschnittliche Bestandsmethode nicht verwenden, wenn Sie nur ein periodisches Inventarsystem verwenden. Da ein solches System nur am Ende jedes Abrechnungszeitraums Informationen sammelt und keine Aufzeichnungen auf der Ebene der einzelnen Einheiten verwaltet. Auch wenn Inventarbewertungen mit Hilfe eines Computersystems abgeleitet werden, macht es der Computer relativ einfach, Bestandsbewertungen mit dieser Methode kontinuierlich anzupassen. Umgekehrt kann es sehr schwierig sein, die gleitende Durchschnittsmethode zu verwenden, wenn Inventurdatensätze manuell beibehalten werden, da das klerikale Personal durch das Volumen der erforderlichen Berechnungen überwältigt würde. Moving Average Inventory Methode Beispiel Beispiel 1. ABC International hat 1.000 grüne Widgets auf Lager am Anfang des April, zu einem Preis pro Einheit von 5. Damit ist die Anfangsbestände-Balance der grünen Widgets im April 5.000. ABC kauft dann 250 zusätzliche greeen Widgets am 10. April für 6 jeder (insgesamt Kauf von 1.500), und weitere 750 grüne Widgets am 20. April für 7 jeweils (insgesamt Kauf von 5.250). In Abwesenheit von Verkäufen bedeutet dies, dass die gleitenden Durchschnittskosten pro Einheit Ende April 5,88 betragen würden, was als Gesamtkosten von 11.750 (5.000 beginnend 1.500 Anschaffungen 5.250 Anschaffungen) berechnet wird, Hand-Einheit zählen 2.000 grüne Widgets (1.000 Anfang Gleichgewicht 250 Einheiten gekauft 750 Einheiten gekauft). Somit waren die gleitenden Durchschnittskosten der grünen Widgets 5 pro Einheit zu Beginn des Monats und 5,88 am Ende des Monats. Wir werden das Beispiel wiederholen, aber jetzt mehrere Verkäufe. Denken Sie daran, dass wir den gleitenden Durchschnitt nach jeder Transaktion neu berechnen. Beispiel 2. ABC International hat ab Anfang April 1.000 grüne Widgets auf Lager, zu einem Preis von 5 Stück. Sie verkauft am 5. April 250 dieser Einheiten und erhebt eine Gebühr für die Kosten der verkauften Waren von 1.250 Wird als 250 Einheiten x 5 pro Einheit berechnet. Dies bedeutet, dass es jetzt 750 Einheiten auf Lager, zu einem Kosten pro Einheit von 5 und einem Gesamtbetrag von 3.750 Einheiten. ABC kauft dann 250 zusätzliche grüne Widgets am 10. April für jeweils 6 (insgesamt Kauf von 1.500). Die gleitenden Durchschnittskosten liegen nun bei 5,25, was als Gesamtkosten von 5.250 geteilt durch die noch vorhandenen 1.000 Einheiten berechnet wird. ABC verkauft dann 200 Einheiten am 12. April und zeichnet eine Gebühr auf die Kosten der verkauften Waren von 1.050, die als 200 Einheiten x 5,25 pro Einheit berechnet wird. Dies bedeutet, dass es jetzt 800 Einheiten auf Lager, zu einem Kosten pro Einheit von 5,25 und einer Gesamtkosten von 4.200. Schließlich kauft ABC weitere 750 grüne Widgets am 20. April für je 7 (insgesamt Kauf von 5.250). Am Ende des Monats betragen die gleitenden Durchschnittskosten pro Einheit 6,10, die als Gesamtkosten von 4 200 5 250 berechnet werden, geteilt durch die insgesamt verbleibenden Einheiten von 800 750. Im zweiten Beispiel beginnt ABC International den Monat mit einer 5.000 Beginnend Balance der grünen Widgets zu einem Preis von 5 jeder verkauft 250 Einheiten zu einem Preis von 5 am 5. April, revidiert seine Stückkosten auf 5,25 nach einem Kauf am 10. April verkauft 200 Einheiten zu einem Preis von 5,25 am 12. April und Schließlich korrigiert seine Einheit Kosten auf 6,10 nach einem Kauf am 20. April. Sie können sehen, dass die Kosten pro Einheit ändert sich nach einem Inventar Kauf, aber nicht nach einem Inventar Verkauf. Application von Diskrete Autoregressive Moving Average Modelle zur Abschätzung der täglichen Abfluss Tiao J. Chang 1 JW Delleur 2 M. L. Kavvas 3 1 Institut für Bauingenieurwesen, Universität Ohio, Athen, Ohio USA 2 Hochschule für Bauingenieurwesen, Purdue University, West Lafayette, IN 47907 USA 3 Department of Civil Engineering, Universität von Kalifornien, Davis, Kalifornien USA erhielt 7. Juni 1985. Angenommen am 13. Oktober 1986. Online verfügbar am 27. März 2003. Der tägliche Niederschlag wurde erfolgreich durch die Modellreihe diskrete Autoregressive Moving Average (DARMA) Modellierung modelliert. Eines dieser Modelle wird in der Schätzung der täglichen Stromströme mittels einer linearen Übertragungsfunktion verwendet. Die statistischen Eigenschaften des gewählten DARMA-Präzipitationsprozesses und die Statistiken der ersten und der zweiten Ordnung der Beziehungen zwischen dem täglichen Niederschlag und dem entsprechenden Stromfluss werden bei der Bestimmung der Übertragungsfunktionsparameter verwendet. Das konstruierte Verfahren wird auf eine Wasserscheide in Indiana angewendet. Die Modellidentifikation, die Parameterschätzung und die Diagnoseprüfung sind dargestellt. Dieses Übertragungsmodell hat den Vorteil, dass es die Statistiken erster und zweiter Ordnung der Niederschlagseingabe und der Abflussausgabe koppelt. Die Modellbeschränkungen stammen aus der Stationarität der DARMA-Modelle, die für die Beschreibung der täglichen Niederschlagsfolgen verwendet wurden. Dies erfordert die Teilung des Jahres in stationäre Jahreszeiten und führt kleine Ungenauigkeiten an der Saison Kreuzungen. Copyright 1987 Erschienen bei Elsevier BV Zitieren von Artikeln () Ein Dokument von VAMOS 1 Wissenschaftliche Studiengruppe auf dem Plata-Becken C. Roberto Mechoso (Ko-Vorsitzender, Kalifornien, Los Angeles, USA), Pedro Silva Dias (Ko-Vorsitzender, U. (USA, Sao Paulo, Brasilien), Walter Baethgen (INIA, Uruguay), Vicente Barros (U. Buenos Aires, Argentinien), E. Hugo Berbery (U. Maryland, USA), Robin Clarke (U. Bundesstaat Rio Grande do Sul, ), Heidi Cullen (IRI, USA), Carlos Erentildeo (CLIVAR International Project Office), Benjamin Grassi (Universidad Nacional de Asuncioacuten, Paraguay), Dennis Lettenmaier (Universität von Washington, USA). 1 Das VAMOS-Panel (Variability of American Monsoon Systems) ist Bestandteil des Klimavariabilitätsprogramms (CLIVAR) im Rahmen des Weltklimaprogramms (WCRP). Inhaltsverzeichnis 1. Einleitung 1.1 Landwirtschaft 1.2 Energiebedarf und Wasserkraft 1.2.1 Privatisierung und Integration 1.3 Grenzüberschreitende Wasserfragen 2. Mittlere Klimatologie des Beckens 2.1 Niedriger Kreislauf 2.2 Feuchtigkeitsfluss und - quellen 2.3 Niederschlag 2.4 Temperatur 3. Mittlere Hydrologie der Basin 3.1 Subbassins 3.2 Hydrologische Regionen 3.3 Zeitliche und räumliche Variabilität hydrologischer Bedingungen 4. Variabilität der Becken Klima 4.1 Mesoskalige Variabilität und der Tageszyklus 4.2 Synoptische Skalenvariabilität 4.3 Intraseasonale Variabilität 4.4 Interannuale Variabilität 4.5 Dezadale Variabilität und Trends 5. Variabilität der Becken Hydrologie 5.1 Flussfluss 5.2 Hochwasser und Trockenheit 6. Ausgewählte relevante Studien mit numerischen Modellen 6.1 Atmosphärische Zirkulationsmodelle (AGCM) 6.2 Mesoskalige Modelle 6.3 Hydrologische Modelle 6.4 Wasserscheide 6.5 Hydrodynamische Modelle 7. Vorhersagbarkeit 7.1 Klima - und Wettervorhersage 7.2 Hydrologie 8. Sensitivität Zum Klimawandel 9 Umweltprobleme 9.1 Landveränderung, Entwaldung und landwirtschaftliche Produktion 9.2 Vermehrte Urbanisierung: Naturgefahren und Verwundbarkeit 9.3 Kritische Regionen für nachhaltige Entwicklung 10. Anwendung der Klimaprognosen: Fallstudien 10.1 Anwendung der Klimaprognosen auf das Wasserressourcenmanagement: Eine Fallstudie von Itaipu 10.2 Anwendung der Klimaprognosen für die Landwirtschaft: eine Fallstudie von Uruguay 10.3 Anwendung der Klimaprognosen zur Urbanisierung: eine Fallstudie von Buenos Aires 11. Motivation für ein internationales Programm auf dem Plata-Flussbecken 12. Relevanz für die Welt (WCRP) 13. Überblick über einen Umsetzungsplan 13.1 Verbesserung der Klima - und Hydrologieüberwachung 13.2 Entwicklung eines Rechenzentrums in der Region 13.3 Entwicklung regionaler Klima - und hydrologischer Vorhersagezentren im Becken 13.4. Entwicklung eines Systems für die Informationsverteilung Eine bedeutende Quelle des natürlichen Kapitals für die wachsenden Bevölkerungsgruppen Argentiniens, Brasiliens, Boliviens, Paraguays und Uruguays, das Plata-Becken erzeugt 70 des gesamten Bruttosozialprodukts dieser Länder und ist für die Ökonomie von entscheidender Bedeutung Ein landwirtschaftliches Zentrum, natürliche Wasserstraße für den Transport und primäre Produzent von Wasserkraft. Angesichts der jüngsten Fortschritte in der Klima - und hydrologischen Prognose besteht ein Potenzial für eine bessere Entscheidungsfindung in Sektoren wie Wasserwirtschaft und Landwirtschaft. Darüber hinaus würden die Bewohner des Plata-Beckens, mittlerweile beinahe 60 der Gesamtbevölkerung der fünf Länder des Beckens, von einem Frühwarnsystem profitieren, das die Auswirkungen extremer Ereignisse wie Dürren und Überschwemmungen verringern könnte. Schließlich ist es notwendig, die signifikante Umweltverschlechterung zu berücksichtigen, die das Becken in den letzten Jahrzehnten infolge der Änderung der Landnutzung und des globalen Klimawandels sowie der Auswirkungen der wirtschaftlichen Entwicklung erfahren hat. Vier Länder des Beckens, Argentiniens, Brasiliens, Uruguays und Paraguays sind derzeit als wirtschaftlicher gemeinsamer Markt (MERCOSUR) tätig. Dies ist eine wichtige Anstrengung für eine engere Integration ihrer Volkswirtschaften. Die Regionalregierungen nutzen den Rahmen von MERCOSUR zur Entwicklung einer gemeinsamen sozioökonomischen Politik. Die wissenschaftliche Gemeinschaft beginnt auch im Rahmen von MERCOSUR regionale Kooperationsforschungsaktivitäten. Die heutige Zeit ist daher besonders günstig für die Etablierung eines internationalen Programms zur Klimatologie und Hydrologie des Plata-Beckens. Das WMO / WCRP-CLIVAR-Gremium zur Variabilität der amerikanischen Monsunsysteme (VAMOS) hat einen allgemeinen Konsens über die Bereitschaft der Regionen gefunden, die kollaborative Forschung über die Plata-Becken-Klima / Hydrologie zu unterstützen und zu unterstützen. Diese Bereitschaft ist vor allem auf ein verstärktes Bewusstsein für die Auswirkungen, die Klimaveränderungen auf das Wasserressourcenmanagement, die Energieproduktion, die Landwirtschaft und die Gesundheit haben können, zurückzuführen. Eine verbesserte Vorhersage kann potenziell zu großen wirtschaftlichen und sozialen Vorteilen für die Region führen. Das Gremium hat auf seiner Jahrestagung in Montevideo, Uruguay, im März 2001 eine VAMOS Plata-Beckenwissenschaftliche Studiengruppe (SSG) ernannt. Mitglieder des Plata Basins SSG sind: Walter Baethgen (INIA, Uruguay), Vicente Barros (U. Buenos Aires, Argentinien), E. Hugo Berbery (U. Maryland, USA), Robin Clarke (U. Federal Rio Grande do Sul, Brasilien), Heidi Cullen (IRI, USA), Carlos Erentildeo (Internationales CLIVAR Projektbüro), Benjamin Grassi (Universidad Nacional de Asuncioacuten, Paraguay), Dennis Lettenmaier (U. Washington, USA), C. Roberto Mechoso U. California, Los Angeles, USA) und Pedro Silva Dias (Ko-Vorsitzender, U. Sao Paulo, Brasilien). Dieses Dokument soll als Leitfaden für die Ausarbeitung eines umfassenden Programms für das Becken dienen. Das Plata-Becken umfasst etwa 3,6 Millionen km 2 (siehe Abb. 1). In geographischer Hinsicht ist das Becken das fünftgrößte in der Welt und an zweiter Stelle nur das Amazonasbecken in Südamerika. Die wichtigsten Sub-Becken sind die der Paranaacute, Paraguay und Uruguay Flüsse. Das Plata-Becken umfasst Teile von fünf Ländern, beherbergt etwa 50 ihrer Gesamtbevölkerung und erzeugt etwa 70 ihres gesamten BSP. Etwa 30 der Fläche gehören Argentinien, 7 nach Bolivien, 46 nach Brasilien, 13 nach Paraguay und 4 nach Uruguay. Das Becken ist auf unterschiedliche Weise für die Volkswirtschaften dieser Länder wichtig. Die Ernten und Viehbestände gehören zu den Regionen, die zu den wichtigsten Gebieten gehören, die Flüsse sind natürliche Wasserwege, und der Oberflächenverkehr ist in den letzten Jahren aufgrund der Integration der regionalen Wirtschaft stark gestiegen. Last, but not least, bieten mehrere Wasserkraftwerke den Großteil der Energie verbraucht. Die Länder im Becken haben eine Geschichte der internationalen Zusammenarbeit. Argentinien und Uruguay bauten Salto Grande am Uruguay. Brasilien und Paraguay bauten das heutige größte Kraftwerk der Welt in Itaipuacute am Paranaacute River. Argentinien und Paraguay gebaut Yacyretaacute, auch ein sehr großes Kraftwerk stromabwärts von Itaipuacute. Das Plata-Becken ist einer der größten Nahrungsmittelproduzenten (Getreide, Sojabohnen und Viehbestand) in der Welt. Die regionale Wirtschaft basiert größtenteils direkt oder indirekt auf der Landwirtschaft (Kulturen und Vieh). Argentinischen Provinzen im Becken produzieren mehr als 90 der Land-Getreide-und Ölpflanzenproduktion, und wachsen mehr als 70 der countrys Rinder. Brasilianische Staaten im Becken produzieren mehr als 30 der Länder Reis, Sojabohnen, Weizen, Mais und wachsen etwa 10 der countrys Rinder. Uruguay produziert seine gesamte Getreide - und Ölpflanze und wächst mehr als 80 seiner Viehbestände im Becken. Paraguay, dessen Wirtschaft weitgehend direkt oder indirekt von der landwirtschaftlichen Produktion abhängt (90 davon entspricht dem Viehbestand), liegt vollständig im Becken. Diese Länderproduktion beträgt etwa 10 Megatonnen (Mt) und steigt durch neue Technologien und den Ausbau der Produktionsbereiche. Die landwirtschaftliche Produktion im südlichen Teil des Plata-Beckens entwickelt sich primär auf den fruchtbaren Böden des Pampas, einem Ökosystem, in dem einheimische gemäßigte und subtropische Wiesen in Ackerland umgewandelt wurden. Dabei führen Klimaschwankungen auf verschiedenen Zeitskalen zu einer hohen Variabilität der Ernte - und Tierproduktion mit dem Potenzial für negative Konsequenzen für die Nahrungsmittelversorgung und die Wirtschaft auf regionaler und nationaler Ebene. Die Pampas erstrecken sich über 75 Millionen Hektar, von denen 26 Millionen angebaut werden. In den letzten zehn Jahren gab es eine beträchtliche Zunahme der Getreideproduktion aufgrund der Einbeziehung der aktualisierten Technologie und der Überarbeitung der unzureichenden Politik für den Sektor. Die durchschnittliche jährliche Produktion der Pampas ist jetzt mehr als 50 Mt, variiert von 45 bis mehr als 65 Mt in den besten Jahren. Die Bereiche der Landwirtschaft in Argentinien haben in den letzten zehn Jahren stetig zugenommen. Bepflanzte Flächen mit Getreide und Ölsaaten erhöhten sich von 20 auf 26 Millionen Hektar. Veränderungen zeigen sich vor allem in den Pampas, wo die Landnutzung stark von den wirtschaftlichen Bedingungen abhängt. (Kultiviertes Landwachstum zum Schaden der Weiden während der Jahre mit günstigeren Preisen für Getreidepflanzen verglichen mit denen für Vieh). Beispielsweise erhöhte sich die Anbaufläche in der Provinz Buenos Aires zwischen 1988 und 1993 um 40. Diese Veränderungen der Landnutzung der Pampas, die die Grenze der Getreideproduktionsgrenze in Richtung Randzone verlagern, erfordern eine Intensivierung der Produktionssysteme, Höhere Einsatznutzung und ein erhöhtes Risiko der Landzersetzung. Dies ist von großer Bedeutung, dass der organische Bodengehalt an einigen Orten auf 50 seines Wertes vor der landwirtschaftlichen Praxis zu Beginn des 20. Jahrhunderts reduziert wurde. Aus diesem Grund und anderen ökonomischen Aspekten wächst das direkte Saatgut oder Minimalabbau rapide. Zu dieser Zeit gibt es mehr als 5 Mio. Hektar unter diesen Arten von Beeten, und es wird geschätzt, dass diese Zahl wird sich mehr als verdoppeln bis zum Jahr 2010. Landwirtschaft in den brasilianischen Staaten Rio Grande do Sul, Santa Catarina und Paranaacute Basiert auf Land, das ursprünglich Teil des Atlantischen Waldes (Mata Atlantica) und der Meridional Wälder und Grasslands Ökosysteme war. Das Ökosystem des Atlantischen Waldes umfasst nahezu die gesamte brasilianische Küstenlinie vom Nordosten bis zum Bundesstaat Rio Grande do Sul. Mehr als 90 dieser Ökosysteme wurden allmählich in landwirtschaftliche Nutzungen seit den frühen 1900er Jahren umgewandelt. Die landwirtschaftliche Produktion im Süden Brasiliens ist stark mechanisiert. Dies führte zu einer hohen Ernteproduktivität, hat aber ernsthafte Umweltprobleme wie Bodenverdichtung und Erosion, Wasserverunreinigung und Vegetationsverwüstung hervorgerufen. Die nördliche Region des Plata-Beckens umfasst Teile des Cerrados-Ökosystems (eine Mischung von Sträuchern und Weiden), die durch niedrige Fruchtbarkeitsböden gekennzeichnet sind, die auch allmählich zu Jahreskulturen (Sojabohnen, Weizen, Mais usw.) umgewandelt werden. 1.2 Energiebedarf und Wasserkrafterzeugung Das weltweit größte Wasserkraftwerk Itaipuacute am Fluss Paranaacute betreibt seit 1982 insgesamt 18 Generatoren (je 700 MW). Die Energieproduktion betrug im Jahr 2000 93,4 Mrd. kWh (Kilowatt Stunden), was etwa 95 der von Paraguay genutzten Energie entspricht, und 24 davon für Brasilien. Itaipuacute ist eine von vielen Pflanzen, die zwischen 1965 und 1985 auf der oberen Paranaacute gebaut wurden (siehe Abbildung 1). Diese Anlagen liefern mehr als 50 des Energiebedarfs Brazilacutes, von denen mehr als 90 aus der Wasserkraft gewonnen werden. Noch mehr Pflanzen sind für die Iguazuacute und andere Nebenflüsse der Paranaacute (insbesondere der Piquiriacute und Ivaiacute) geplant. Das Uruguay-Flussbecken hat auch ein großes Wasserkraftpotenzial, die gesamte verfügbare Energie liegt bei 16.500 MW, wovon bisher 6680 MW entwickelt wurden. Vorhandene Entwicklungen sind auf dem Passo Fundo River, und auf Salto Grande, auf der internationalen Reichweite zwischen Argentinien und Uruguay. Letzteres Land hat drei Wasserkraftwerke auf dem Negro River gebaut. Unter diesen war Gabriel Terra, gebaut 1945, der erste Damm, der auf einer Hochebene errichtet wurde, und sein Reservoir war das größte in der Welt. Die Flüsse des Plata-Beckens bilden auch die primäre Wasserversorgung für ein dicht besiedeltes Gebiet, zu dem auch Buenos Aires und Satildeo Paulo gehören, die beiden größten Städte Südamerikas. Das Wachstum des Strombedarfs hat in vielen Ländern des Plata-Beckens 5 überschritten, und es wird zunehmend besorgt, dass der Bau neuer Stromerzeugungsanlagen nicht mit dieser Nachfrage Schritt halten wird. Die starke Abhängigkeit von Wasserkraft macht die Becken Stromversorgung anfällig für Dürre und Wassermangel. Was die Wasserressourcen anbelangt, so haben die großen Wasserkraftwerke, die in den letzten 30 Jahren gebaut wurden, einen erheblichen Einfluss auf das Flussregime des Beckens gehabt. Das Becken ist auch die Heimat von Guarany, einer der weltweit größten Aquiferen, die 1,2 Millionen km 2 im Paranaacute-Becken mit Reserven auf 50.000 km geschätzt erweitert. 1.2.1 Privatisierung und Integration Die jüngste Umstrukturierung des Strommarktes innerhalb der MERCOSUR-Länder Argentinien, Brasilien, Paraguay und Uruguay wurden entwickelt, um Wasserkraftprojekte für Privatanleger attraktiver zu machen. Derzeit ist der Bau auf dem Weg zu bauen Brazils größten privatisierten Wasserkraft-Projekt auf den Uruguay River genannt Itaacute. Dies ist eines der ersten großen Staudammprojekte, die von der Interamerikanischen Entwicklungsbank (IDB) als Teil der neuen privaten Finanzierungsinitiative der IDB gefördert werden. Auch Teil dieser Initiative ist der Plan für 16 Dämme in Brasilien, die für Angebote von privaten Unternehmen aufgestellt werden. Die prognostizierte Wachstumsrate des Strombedarfs für Südbrasilien beispielsweise beträgt etwa 5,8 pro Jahr, vor allem wegen der massiven Investitionen in wachsende Wirtschaftszweige wie die Automobil - und Petrochemieindustrie. Deregulierung ist eine Strategie, um der steigenden Nachfrage gerecht zu werden. Die Verwendung von saisonalen bis hin zu interpersonalen Klimaprognosen kann auch dazu beitragen, höhere Effizienz zu erreichen, um die steigende Nachfrage besser befriedigen zu können. Tabelle 1. Alle Zahlen stammen aus der Energieinformationsverwaltung eia. doe. gov/ und dem CIA Factbook cia. gov/cia/publications/factbook/geos. Zahlen berichtet für 1998. Wachsende Nachfrage nach Strom in ganz Südamerika hat dazu beigetragen, die Vernetzung der Regionen verschiedene Stromnetze zu fördern. Dieser Trend dürfte sich aufgrund der weiteren Deregulierung des Stromsektors und der Lockerung der Beschränkungen internationaler Investitionen fortsetzen. Brazils Energie-Sektor ist in der Mitte eines Wandels von Staat zu privater Kontrolle. Nach Angaben der brasilianischen Entwicklungsbank wurden im Jahr 1999 fünf brasilianische Energieversorger privatisiert. Argentinien und Bolivien haben auch versucht, die Produktivität im Energiesektor zu steigern, indem sie Vermögenswerte vom Staat in den privaten Sektor transferieren. Seit 1991 verfolgt Argentinien aggressiv die Privatisierung. Brasilien und Chile sind die beiden wichtigsten Exportmärkte für Argentinien, und diese drei Regierungen arbeiten daran, ihre Strommärkte zu integrieren. Im Jahr 1994 verabschiedete Bolivien ein Gesetz, das es privaten Firmen erlaubte, 50 Eigentumsrechte an Vermögenswerten zu erwerben und die Fähigkeit zur Bewirtschaftung von Anlagen zu erlangen. Brazils kleine nördliche und größere südliche Stromnetze wurden im Januar 1999 zu einem Netz verbunden, das 98 des Landes dient. Die Verbindung zwischen den elektrischen Systemen von Argentinien und Uruguay ist seit 1974 in Kraft. Ein Projekt mit einer Leistung von 230 Millionen Euro ist in vollem Gange, um Brasilien mit Ursprung aus Argentinien mit 1.000 MW Leistung zu versorgen. Electrosul von Brasilien hat eine Vereinbarung mit Uruguay für den Kauf von 70 MW Energie, wird das Projekt geschätzt, 30 Millionen kosten. Vier Unternehmen untersuchen derzeit das Potenzial, Strom aus Bolivien nach Brazils Matto Grosso zu exportieren. Aufgrund seines großen Erzeugungspotentials analysiert Bolivien derzeit auch mehrere Projekte zur Stromexpansion, um die Nachfrage in Brasilien zu decken. 1.3 Grenzüberschreitende Wasserprobleme Die nachhaltige Entwicklung begrenzter natürlicher Ressourcen hängt von einem effektiven Dialog zwischen Wissenschaftlern, Entscheidungsträgern, Ressourcenmanagern und Endnutzern ab. Das Plata-Becken ist ein komplexes System, geprägt durch natürliche Prozesse und menschliche Anforderungen, die jeweils räumliche und zeitliche Variabilität aufweisen. In Südamerika sind grenzüberschreitende Wasserfragen zunehmend an Bedeutung gewachsen, obwohl dies nur 5 der Weltbevölkerung und 26 der Weltenabflüsse hat. Eine nachhaltige Entwicklungsstrategie für Grenzgebiete muss Folgendes umfassen: a) Diagnostik der einzelnen Gebiete, b) Umweltzonierungsvorschläge, die Bereiche definieren, die für eine nachhaltige Produktion sowie Gebiete für den Umweltschutz geeignet sind, (c) integrierte Programme, die Teil eines Gesamtentwicklungsstrategie und d) nationale und binationale Investitionsprojekte, die auf der Ebene der Machbarkeit und Machbarkeit formuliert wurden. 2. Mittlere Klimatologie des Beckens 2.1 Niedrige Zirkulation Das meridionale Windfeld bei 850 mb von ECMWF-Reanalysen, die in Abb. Fig. 2 zeigt die wichtigsten Oberflächenzirkulationsmerkmale. Die Winde auf dieser Ebene sind nördlich über den meisten Becken mit einem Maximum in der nordwestlichen Sektor Norden liegen das ganze Jahr über, aber sind am stärksten im Winter. Der nordöstliche Sektor zeigt die Signatur der südatlantischen Konvergenzzone (SACZ), die einen gut definierten Jahreszyklus mit der stärksten Intensität im Sommer hat. Schätzungen des Jahreszyklus von anderen globalen Analysen, während ähnlich über die SACZ, können sehr unterschiedlich östlich der Anden. Eine ähnlich breite Beschreibung wurde für den Feuchttransportbereich über Südamerika erzielt (Nogueacutes-Paegle und Mo, 1997). Wir werden auf diesen Punkt später in diesem Dokument zurückkommen. Die Sommerzirkulation über Südamerika wird von einem Monsunsystem (SAMS) dominiert. Wichtige geographische Faktoren, die die Monsunentwicklung bestimmen, sind die vom Äquator geteilte große Landmasse, sehr hohe Berge im Westen, die den Luftverkehr in der zonalen Richtung effektiv blockieren und die Oberflächenbedeckung, die von den tropischen Wäldern in Amazonien bis zu Höhenwüsten im Bolivien variiert Altiplano. Reichliche Feuchtigkeitsversorgung aus dem Atlantik unterhält ein Niederschlags-Maximum über Zentral-Brasilien. Ein wichtiges saisonales Merkmal der monsoonal Zirkulation über Südamerika ist die südliche Atlantische Konvergenz-Zone (SACZ), die sich südöstlich entlang der nordöstlichen Grenze des Plata-Beckens während der Sommersaison erstreckt. Die SACZ ist in mehrfacher Hinsicht ähnlich der südpazifischen Konvergenzzone (SPCZ), die sich über den südwestlichen tropischen Pazifik entwickelt. Dieses Dokument unterstreicht die wichtige Rolle der SACZ über die Variabilität der Niederschläge im Plata-Becken. Abbildung 2. Jährlicher Zyklus des monatlich mittleren Meridionalwindes (ms -1) auf der 850 hPa-Ebene aus der ECMWF-Reanalyse. Ein nordöstlich / nordöstlich östlich der Anden (SALLJ) gelegenes, nordöstlich der Anden (SALLJ) ist ein wichtiges klimatologisches Merkmal des Plata-Beckens (z. B. Virji, 1981). Bis zu einem gewissen Grad ist die SALLJ das Gegenstück zu der Low-Level-Jet, fließt Nordwesten über die Great Plains der USA (GPLLJ). Die GPLLJ entwickelt sich vor allem während der borealen warmen Jahreszeit, während die SALLJ scheint die meisten des Jahres zu präsentieren (Nogues-Paegle und Berbery, 2000 siehe auch met. utah. edu/jnpaegle/research/miamireport. html Ein Feldversuch, um erweiterte Beobachtungen des SALLJ zu erhalten, werden in met. utah. edu/jnpaegle/research/ALLS. html beschrieben. Abbildung 3. Durchschnittliche monatliche Winde (m / s) bei 850 hPa nach NCEP / NCAR-Reanalyse 1958-1992. Abbildung 3 gibt einen vereinfachten Überblick über den Jahreszyklus der niedrigen Zirkulation über Südamerika. Im Januar gibt es einen wichtigen Zufluss aus dem tropischen Atlantik aus der nördlichen Hemisphäre. Dieser Fluss verläuft nach Osten über den tropischen Kontinent und dann südwärts mit einer starken Strömung entlang der Ostflanke der Anden. Bei 20deg-25deg S ist der Wind von Norden ganz über dem Kontinent östlich der Anden. Dieser Fluss neigt dazu, sich in zwei Zweige nach Südwesten und Südosten zu teilen. Im April ist der mittlere Wind etwas ähnlich dem im Januar, aber die tropischen Ostländer in der südlichen Hemisphäre haben eine südliche Komponente. Die nördliche Komponente gegenüber dem subtropischen Südamerika ist deutlich schwächer als im Januar. Süden von ungefähr 25deg S ist der Fluss hauptsächlich nach Süden. Im Juli scheint der niedrige Fluss über dem größten Teil des Plata-Beckens mit dem südatlantischen Hoch assoziiert zu sein. Die meisten Merkmale des Sommerflusses sind bereits im Oktober vorhanden. 2.2 Feuchtigkeitsfluss und Quellen Ein vollständiges Verständnis der Plata-Becken-Hydrologie erfordert Kenntnisse der atmosphärischen Komponente des Wasserkreislaufs. Dies ist jedoch zum jetzigen Zeitpunkt aufgrund der fehlenden Beobachtungsdaten sehr begrenzt, da an jedem Ort nur etwa zehn Radiosonden einmal pro Tag gestartet werden. Die kleinen räumlichen Skalen des SALLJ verschärfen die Schwierigkeiten mit der Datenknappheit. Globale Analysen wurden verwendet, um vorläufige Beschreibungen der Feuchtigkeitsflüsse zu erhalten. Nogueacutes-Paegle und Mo (1997) dokumentierten die Feuchtigkeitsströme aus den Tropen in Argentinien, im südlichen Brasilien und im nördlichen Uruguay mit Hilfe von NCEP / NCAR-Reanalysen. Ihre Ergebnisse deuten darauf hin, dass, während die Feuchtigkeit Quelle der GPLLJ ist eine Wassermasse (der Golf von Mexiko), hat die SALLJ eine kontinentale Feuchtigkeit Quelle. Große Unterschiede ergeben sich jedoch, wenn man versucht, mit Hilfe von globalen Analysen aus verschiedenen operativen Zentren die Feuchtebudgets auf regionalen Skalen zu berechnen (Wang und Paegle, 1996). Darüber hinaus verringert die Verwendung von neueren Reanalyseprodukten (Higgins et al., 1996) diese Diskrepanzen nicht. Ein möglicher Grund ist die unzureichende zeitliche Auflösung des Reanalysedatensatzes, der den Tageszyklus nicht erfassen kann. (Berbery und Rasmusson, 1999) Die Stichprobenhäufigkeit muss mindestens viermal pro Tag betragen, um zuverlässige Schätzungen der atmosphärischen Wasserbilanz für die Mississippi-Subbecken zu erhalten. Es gibt Hinweise darauf, dass sogar 4 Analysen pro Tag nicht ausreichen, um die Komplexität des Tageszyklus der Feuch - tigkeitsflusskonvergenz zu lösen (Berbery und Collini, 2000). Der jährliche mittlere Niederschlag im Plata-Becken beträgt etwa 1.100 mm, von denen nur etwa 20 (23.000 m 3 s -1) das Meer als Oberflächenwasser erreichen. Die anderen 80 werden verdampft und in den Boden infiltriert. Es ist offensichtlich, dass jede kleine prozentuale Veränderung der Verdampfungs - und Infiltrationsrate zu größeren prozentualen Änderungen im Abfluss führen kann. Aufgrund der Veränderungen in der Vegetationsdecke in den meisten mittleren und oberen Paranaakuten, im mittleren und unteren Paraguay und im oberen Uruguay (siehe Abschnitt 9.2) können die menschlichen Aktivitäten in den letzten 50 Jahren zu einer Änderung des Abflusses geführt haben. Dämme können auch die Verdunstung ändern, wenn auch wahrscheinlich mit einer niedrigeren Geschwindigkeit. Der jährliche mittlere Niederschlag im Plata-Becken neigt sowohl von Nord nach Süd als auch von Ost nach West (Abb. 4). Entsprechende Mengen reichen von 1.800 mm in den Seehöfen entlang der brasilianischen Küste bis zu 200 mm entlang der westlichen Grenze des Beckens. Der Niederschlag ist im Oberlauf der Flüsse Paraguay und Paranaacute groß. Die Amplitude des Jahreszyklus bei Niederschlägen nimmt von Norden nach Süden ab (Bild 5). Der nördliche Teil des Beckens hat einen gut definierten Jahreszyklus mit maximalem Niederschlag im Sommer (Dezember-Februar). Die zentrale Region (Nordost-Argentinien / Süd-Brasilien) hat eine einheitlichere Saisonverteilung, mit Maxima im Frühjahr und Herbst. Da die großen Flüsse im Becken im Allgemeinen von Norden nach Süden laufen, trägt dieses Niederschlagsregime zur Dämpfung des saisonalen Zyklus nachgeschaltet. Rund 20deg-25degS, verstärkte Niederschläge im Sommer ist die Signatur der SACZ Entwicklung, vor allem nach Osten. Im Winter und im Frühling ist dagegen ein verstärkter Niederschlag die Unterschrift einer erhöhten baroklinen Aktivität. Während die Häufigkeit der Cyclogenese in diesen beiden Jahreszeiten nahezu gleich ist (Gan und Rao, 1991), ist der Wasserdampfgehalt der Atmosphäre höher und der Niederschlag im Frühjahr größer (Rao et al., 1996). Die mittlere Jahrestemperatur im Becken reicht von etwa 15 ° C im Süden bis über 25 ° C im Nordwesten. Die meisten Orte östlich der Anden weniger als 800 km vom Meer haben eine durchschnittliche jährliche Temperatur unter 20degC. Die höheren Lagen im östlichen Teil der brasilianischen Staaten Satildeo Paulo, Paranaacute und Santa Catarina sind wesentlich kühler als ihre Umgebung. Im Winter weisen die Monatsmitteltemperaturen eine deutliche Nord-Süd-Steigung auf. Im Juli zum Beispiel ist die mittlere Temperatur über dem nordwestlichen Teil des Beckens mehr als 20 ° C, während die in der Provinz von Buenos Aires ist etwa 10degC Kühler. Im Sommer ist die Steigung mehr zonal reagiert auf die Land-Ozean-Verteilung. Im Januar liegen die Höchsttemperaturen im Chaco und im Westen Argentiniens bei über 27,5 ° C, während sie in den Küstengebieten Südbrasiliens, Uruguays und der Provinz Buenos Aires weniger als 22,5 ° C betragen (Hoffmann 1975). 3. Mittlere Hydrologie des Beckens Das hydrologische Verhalten der Hauptflüsse, die das Plata-Becken entwässern, wird stark von der Becken-Topographie - selbst ein Produkt von Geologie und Klima - sowie von menschlichen Aktivitäten beeinflusst (siehe Tabelle 2). Topographische Höhen haben starke meridional (die allgemeine Richtung der Entwässerung) und Zonenschwankungen. Die östliche Grenze des Beckens hat eine mittlere Höhe von 1000 m, obwohl die Wasserscheide so hoch wie 1500 m im Osten und so niedrig wie 200 m im Süden sein kann. Die westliche Grenze umfasst die Anden-Berge, die Höhen zwischen 1000 und 4000 m zu erreichen. Es gibt jedoch Strecken im Nordwesten und Südwesten, wo Höhen nur etwa 500 m bzw. 300 m erreichen. Der Paranaacute River entspringt am Zusammenfluss der Flüsse Paranaiba und Grande im Südosten Brasiliens (Abb. 1), und Strecken des Flusses markieren die Grenze zwischen Paraguay und Brasilien sowie Paraguay und Argentinien. Die Paranaacute fließt hauptsächlich durch die Ebenen von Paraguay und Argentinien vor dem Beitritt zum Uruguay River an der Spitze des Plata River. Der Hauptquartier von Paranaacutes ist der Paraguay River, der aus Zentralbrasilien stammt. Die arme natürliche Drainage der Region, durch die das Paraguay fließt, hat das Pantanal, eines der weltweit größten Feuchtgebiete mit einer Fläche von 140.000 km 2, geschaffen (Bild 1). Der Pantanals-Hang ist 0,25 m km -1 in Ost-West-Richtung, aber nur 0,01 m km - 1 in Nord-Süd-Richtung. Solch ein sehr flacher Hang erzeugt eine Zeitverzögerung im Hochwasserschnee zwischen dem Norden und dem Süden des Pantanal von ungefähr vier Monaten. Abbildung 4. Jährliche mittlere Niederschlagsmenge im Plata-Becken von XieampArkin. Abbildung 5. Monatlich-mittlere Niederschlagsmenge im Plata-Becken (Xie und Arkin, 1997). Das Flußregime im gesamten Paraguay als Ganzes wird stark durch den Pantanal-Speicher beeinflußt, eine Folge davon, daß die jährlichen Höchstwerte im Oberen Paraguay zwischen einem Jahr und dem nächsten unabhängig von den Niederschlagsverhältnissen korrelieren. Zwischen dem Pantanal und Corrientes in Argentinien, wo die Paraguay schließt sich der Paranaacute, die mittlere Steigung ist etwa 0,04 m km -1. Der Uruguay River beginnt im Serra do Mar und definiert die Grenze zwischen den Staaten Santa Catarina und Rio Grande do Sul in Brasilien. Von dort aus markiert es die Grenze zwischen Argentinien und Brasilien bis zu seiner Konvergenz mit dem Cuareim-Fluss, wo es die Grenze zwischen Argentinien und Uruguay. Der wichtigste Nebenfluss des Uruguay River ist der Negro River, der aus Brasilien stammt und Uruguay von Nordosten nach Westen kreuzt. Die Gesamtlänge von Negros und die Fläche des Beckens betragen etwa 850 km bzw. 71.200 km2. 3.2 Hydrologische Regionen Das Plata-Becken ist eine Kombination aus mehreren Regionen mit unterschiedlichen hydrologischen Eigenschaften. In den oberen Paranaacute und Paraguay-Becken, tritt die Regenzeit im Sommer. Im Uruguay-Becken hingegen findet im Winter eine Hochstromsaison statt. Basierend auf hydrologischen Eigenschaften kann das Plata-Becken in sechs Regionen aufgeteilt werden: Obere Paranaacute. Diese Region erstreckt sich von den Ursprüngen des Einzugsgebietes bis zum Zusammenfluss mit der Iguazuacute. Der obere Teil hat eine signifikante Veränderung der Bodenbedeckungseigenschaften erlebt, die in einigen Teilen von 90 bis etwa 5 Jahren in 50 Jahren zurückgegangen ist (Tucci et al., 1999). Ober-Paraguay. Diese Region erstreckt sich von den Ursprüngen bis zur Apa, an der Grenze zwischen Paraguay und Brasilien, unterhalb von El Pantanal. Bermejo und Pilcomayo Flüsse. Die Becken dieser Flüsse sind die größten Produzenten von Sedimenten. Uruguay. Dies ist ein Becken mit signifikanten Veränderungen der Bodenbedeckung Merkmale. Mittlere und untere Paranaacute und Paraguay. Diese Region zeichnet sich durch breite Überschwemmungsgebiete aus, die während großer Überschwemmungsereignisse über lange Zeiträume hinweg überflutet werden, aber einen kleinen Beitrag zur gesamten Flussentleerung leisten. La Plata River. This is a shallow-water system significantly influenced by meteorological and astronomical tides. It may be separated into upper and lower parts. As is to be expected in an area as large as the Plata Basin, the principal matters of hydrological concern vary considerably between sub-basin and from upper to lower reaches. In the Upper Paranaacute River, above the confluence with the Iguazuacute River, the principal factor is the use and operation of the huge hydropower production, and the change in land use from natural forest to arable cropping systems based on soybean production. In the lower courses of the Paraguay and Paranaacute Rivers, the principal matters of hydrological concern are navigation, and flood control. In the recent past, floods on those rivers have caused significant loss of life and damage to property. Table 3. A comparison between the Plata and Mississippi River Basins. Figure 6. Satellite view of flooded areas during January 1998. 3.3 Temporal and spatial variability of hydrological conditions The variability in soil moisture, soil cover and soil use can have important impacts on the water cycle. The flooded area of the Pantanal can increase from 10,000 km 2 during dry periods to more than 140,000 km 2 during flood periods with potential implications for atmosphere-land surface feedbacks. Another area of strong variability is on the Middle and Lower Paranaacute, which may have large areas flooded during several months in big floods (Fig. 6). 4. Variability of the Basins Climate 4.1 Mesoscale variability and the diurnal cycle The atmospheric water cycle of the Plata Basin is significantly influenced by mesoscale variabilities asociated with the SALLJ (Wang and Paegle, 1996 Berbery and Collini, 2000). The SALLJ has a diurnal cycle with a nighttime maximum that favors increased moisture flux convergence in the Plata Basin. This convergence, in turn, is associated with generalized nighttime ascent and precipitation. A second precipitation regime is found toward the eastern part of the basin, where largest values during daytime appear to be associated with a convectively unstable atmosphere, with convection being triggered by a sea breeze enhanced by the topography of southern Brazil. Figure 7. Diurnal cycle of moisture flux convergence over the Plata Basin during spring. The diurnal cycle of moisture flux convergence for the entire basin is shown in Fig. 7 (Berbery and Collini, 2000). The afternoon maximum of convergence can be associated with the sea breeze/topographically forced diurnal regime on the eastern part of the region, while the nighttime maximum (between 6 and 9 UTC) is associated with SALLJ variations. 4.2 Synoptic scale variability During the austral winter, the subtropical jet stream is strongest and closest to the equator and precipitation in the basin is primarily associated with extratropical cyclones. The south-western Atlantic Ocean just off the South American coast between 30 deg S and 45 deg S is one of the regions with the highest cyclogenetic activity in the Southern Hemisphere. Eastward traveling cyclonic systems that develop over the ocean can intensify after reaching the continent and follow trajectories along the coast. Sea surface temperature (SST) gradients can have a significant influence on the trajectories of these cyclones and their associated sensible and latent surface heat fluxes (Saraiva and Silva Dias, 1997). Frontal systems move rapidly over land regions of low specific humidity and high loss of heat by radiation, and are not generally associated with strong convective activity. Cold surges, known as friagens can reach as north as central and southern Brazil (Parameter, 1976 Hamilton and Tarifa, 1978 Fortune and Kousky, 1983 Marengo et al. 1998) and have large economic consequences. Synoptic scales waves move across the basin. For cyclonic disturbances, the low-level perturbation intensifies at around 1,000 km east of the Andes mountains. Rainfall accumulated over cyclonic episodes amounts to more than 60 of the mean winter accumulated precipitation over central Argentina. This precipitation is associated with an increased contribution of moisture from the tropics along the eastern flank of the Andes Mountains, and positive anomalies of the atmospheric column water content (Vera et al. 2001). 4.3 Intraseasonal variability Variability of the SACZ is of primary importance for precipitation variability in the Plata Basin during summer. Anomalies in rainfall over the SACZ tend to be out-of-phase with anomalies over adjacent regions to the south (e. g. Nogueacutes-Paegle and Mo, 1997 Aceituno and Montecinos, 1997). Several studies agree that convection variability over South America is characterized by a dipole-type pattern with centers over the SACZ and the subtropical plains. Namely, when the SACZ is enhanced and associated precipitation/upward motion increase then subsidence increases and precipitation decreases to the south. Conversely, when the SACZ is weakened and associated precipitation/upward motion decrease, subsidence decreases and precipitation increases to the south. Such dipole-type variability is modulated by modes with different time scales. It has been suggested that the Madden-Julian Oscillation (MJO) propagating along the tropics modulates the northward component of the dipole associated with SACZ variability (Nogueacutes-Paegle and Mo, 1997). The southern component of the SACZ dipole is modulated by a higher frequency (22-28 day) mode that extends from the central Pacific eastward and southward from mid-latitudes before curving northeast towards South America. Convection variability in the SPCZ has been linked to that in the SACZ through southeastwardly propagating waves that curve toward the northeast over South America (Kiladis and Weickmann, 1992 Grimm and Silva-Dias, 1995 Liebmann et al. 1999). 4.4 Interannual variability Several studies have found links between ENSO events in the equatorial Pacific Ocean and rainfall anomalies during late austral spring-early summer and late austral fall-early winter in extratropical South America. Here, there are significant negative correlations between rainfall and the Southern Oscillation Index (SOI) during October-November (Aceituno, 1988). Rainfall anomalies in northeastern Argentina, southeastern Brazil and Uruguay tend to be positive from November of El Nintildeo years to February of the following years and negative from July to December of La Nintildea years (Ropelewski and Halpert, 1987,1989). In the same area but also in Paraguay there is a positive and significant difference in spring precipitation between El Nintildeo and La Nintildea (Kiladis and Diaz, 1989). There are also detailed studies on the interannual response of the precipitation to the warm and cold phases of ENSO in some regions of the Plata Basin. Precipitation correlates significantly with ENSO indexes during the austral spring in the south of Brazil (Rao and Hada, 1990 Grimm et al. 1998) with similar signals during the winter. In Uruguay and southern Brazil rainfall tends to be higher than average in El Nintildeo years, especially during November-January, and lower than average in years with a high index phase of the Southern Oscillation (HSOI years), especially in October-December (Pisciottano et al. 1994). In addition, rainfall anomalies tend to switch signs during January and February (late austral summer) after HSOI years, but not after El Nintildeo years. These precipitation anomalies during ENSO events are associated with atmospheric circulation anomalies. Over most of southeastern South America in spring during warm (cold) ENSO events, the subtropical jet and cyclonic activity are enhanced (weakened). During most of the warm (cold) ENSO events, the Chaco low deepends (weakens) and the moisture advection from the north increases (Grimm et al. 2000). The leading empirical orthogonal function (EOF) mode of both wind components in the upper troposphere over South America during summer from the NCEP reanalysis consists of a strong, anomalous, large-scale eddy circulation over the SACZ (Robertson and Mechoso, 2000). An anomalous cyclonic (anticyclonic) eddy was found to accompany an intensified (diffuse) SACZ, with anomalous descent (ascent) to the southwest. At low levels, an intensified (weakened) SACZ was found to be associated with a weak (strong) flows east of the Andes. Interannual variability in the January-March period appears to be largely uncorrelated with ENSO, while it exhibits strong correlations with SSTs over the south west Atlantic (Robertson and Mechoso, 2000). However, similar SACZ circulation patterns also occur during the October-November period, at which time they are strongly teleconnected with ENSO (G. Cazes, A. W. Robertson and C. R. Mechoso, pers. comm. 2000). This marked seasonality in ENSO teleconnections is consistent with the findings of Pisciottano et al. (1994) who found the strongest ENSO influence on Uruguay rainfall to be in the spring. During the austral spring of El Nintildeo years, the SACZ is weakened accompanied by enhanced ascent to the southwest and an intensified southward flow east of the Andes, consistent with positive rainfall anomalies over Uruguay. During summer, increased (reduced) precipitation in southern Brazil, most of Uruguay and northeastern Argentina are likely to be associated with a weaker (stronger) SACZ, and with increased (reduced) rainfall further south in Argentina (Barros et al. 2000a). Barros et al. 2000 have also found meridional displacements of the SACZ to be important for precipitation, and that warm (cold) SST anomalies over the southwestern Atlantic (20degS - 40degS, west of 30degW) are likely to be accompanied by a southward (northward) shift of the SACZ. The precipitation field in southeastern South America is also affected in other seasons by SST anomalies in the neighboring Atlantic Ocean (Diaz et al. 1998 Barros et al 2000a). 4.5 Decadal variability and trends Rainfall variability in most of southern South America has important interdecadal components. The strongest interdecadal variability in the annual cycle of precipitation occurs in regions of transition between precipitation regimes, especially in the Paranaacute River Basin (Rusticucci and Pentildealba, 1997). In subtropical Argentina the annual precipitation also shows oscillations with periods from 7 to 10 years (Pentildealba and Vargas, 1993 Minetti et al. 1982 Minetti and Vargas, 1983). On this time scale there is a close relationship between the temperature and precipitation regimes (Rusticucci and Pentildealba, 1997). Precipitation trends in Argentina have been positive since 1916 and even increased after the late fifties (Castantildeeda and Barros, 1994). This behavior is consistent with a climatic jump around the 1960s, when the southern portion of South America experienced a significant warming (Vargas et al. 1995). Precipitation increased by up to 30 between 1956 and 1991 in several localities between 20deg S and 35deg S east of the Andes (Castantildeeda and Barros, 1994). In a large part of this region, most of the increase occurred during the 1960s, and it seems to have been associated with a reduction of the meridional gradient of surface temperature, which probably caused a southward shift of the regional circulation. Consistently, the leading principal component of annual precipitation correlates with the meridional gradient of temperature at interannual as well as interdecadal timescales (Barros and Doyle, 1996). Another strong precipitation increase was observed during late 1970s. This correlates with an increase in the subtropical temperature of the Southern Hemisphere and a decrease of the SOI (Barros and Doyle, 1996). The positive trend in precipitation during 1956-1991 has facilitated a southward extension of the agricultural frontier in Argentina increasing available lands by the 1960s in an amount that exceeds 100,000 km 2 (Barros et al, 2000b). Trends in precipitation over the basin prior to the 1960s have also been detected. A linear trend has been reported in the monthly and annual rainfall in part of the province of Buenos Aires (Pentildealba and Vargas, 1996). Decreased precipitation in subtropical Argentina tends to be associated with enhanced westerly flow in Patagonia (Schwerdtfeger and Vasino, 1954). The negative trend in the subtropical region in the period 1931-50 could be associated with a slowing of the westerlies over Patagonia. Significant negative correlations have been obtained between the westerly flow and rainfall in eastern Argentina (Diacuteaz, 1959). It has been suggested that when the zonal circulation is strong in the tropical Atlantic, the Hadley cell is weaker over the South American sector, which leads to a poleward displacement of the subtropical highs and to larger rainfall in the subtropical region (Pittock, 1980). These features are consistent with the notion that in a large region of subtropical South America east of the Andes, the periods of time in which systems are displaced anomalously far south tend to be associated with larger than average rainfall. The opposite occurs when the systems are displaced anomalously north. A near-cyclic 15-year component has been found in the leading mode of SACZ circulation anomalies (Robertson and Mechoso, 2000). This periodicity was corroborated from independent analyses of southwest Atlantic SSTs and river flows (see section 5.1). 5. Variability of the Basins Hydrology Several studies have addressed the variability of river streamflow in the Plata Basin (e. g. Aceituno, 1988 Mechoso and Perez-Iribarren, 1992 Marengo, 1995 Garciacutea and Vargas, 1998 Genta et al. 1998 Garciacutea, 1999 Bischoff et al. 2000 Camilloni and Barros, 2000). The annual streamflow of the Negro, Paraguay, Paranaacute, and Uruguay Rivers during the period 1911-93 includes a nonlinear trend and a near-decadal component (Genta et al. 1998 Robertson and Mechoso, 1998). On the decadal time scale, high river runoff is associated with anomalously cool SSTs over the tropical North Atlantic, with the strong signal in the Paraguay and Paranaacute Rivers during summer. Interannual streamflow peaks with ENSO time scales were only found to be significant in the Negro and Uruguay Rivers in the southeast. Here, El Nintildeo is associated with enhanced streamflow. The interannual-to-decadal variability of the SACZ has an interdecadal 15-year component that is also present in river flow (Robertson and Mechoso, 2000). When the SACZ is intensified, the Paranaacute River in southern Brazil tend to swell while the Uruguay and Negro Rivers to the south tend to ebb. The interdecadal component was found to be much stronger in the north-south gradient of streamflow anomalies than in the streamflows themselves. The Paranaacute River is directly influenced by the SACZ. The Uruguay-Negro Rivers to the south are influenced in the opposite sense through the dipole in vertical motion, and possibly by accompanying variations in southward moisture transport by the SALLJ. A 14-16-year interdecadal component in broad-scale SSTs and sea-level pressures over the South Atlantic has been documented by Venegas et al. (1998). A strengthening (weakening) of the subtropical anticyclone over the South Atlantic is found to accompany negative (positive) broad-scale underlying SST anomalies. This mode bears spatial and temporal similarities to that found by Robertson and Mechoso (2000), so that the latter may be the regional counterpart of basin-scale South Atlantic variability. There is evidence of changes in the annual runoff cycle before and after 1983 (Camilloni and Barros, 2000). The maximum discharge changes from February (before 1880) to autumn (after 1983) in Corrientes and Posadas, together with an important increment in the mean annual discharge. These changes may be due to climate variability, river regulation by dams and/or runoff change because of changes in soil use. The climate signal is consistent with an increasing trend in the precipitation over the upper and middle Paranaacute basin during the fall season (Camilloni and Castantildeeda, 2000). River regulation by dams is a direct consequence of the annual cycle of precipitation and the overriding share of hydropower offer in the Brazilian energy matrix, which requires to save part of the waters for autumn and winter use. 5.2 Flood and drought Flooding is of major concern in the Plata Basin. Most rivers have long and wide flood plains, which have been settled and cultivated. Over a considerable period of time (1950-73), annual floods were not extensive. This encouraged the belief that settlements could be built in locations that were subsequently shown to be at severe risk of flooding. The largest flood of the century occurred on the Paranaacute River in 1983 during a strong ENSO event. For a year and a half after the event, the Paranaacute flood level was above street level in parts of Santa Feacute, Argentina (Tucci and Clarke, 1998). In Uniatildeo da Vitoacuteria on the Iguazuacute River, the cost of the flood amounted to US78 million. In the state of Santa Catarina the damages represented 8 of that states gross product for the year. Losses for floods in Argentina during the 1983 and 1992 episodes exceeded US1 billion each. The four greatest peak discharges in the middle Paranaacute on record occurred during May to July, following the El Nintildeo years of 1983, 1904, 1992 and 1998, when there were strong and positive SST anomalies in the Nintildeo-3 region. Also, whenever SST in Nintildeo-3 remains warmer during those months, there are large discharges on the middle Paranaacute, with a magnitude directly proportional to that of the of SST anomalies. In addition, for every El Nintildeo event since 1976, SST anomalies in Nintildeo-3 have been positive during the austral autumn of the following year, which suggests a phase change in the EN events. In this context, the probability of other event similar to 1983 is higher than what could be inferred from a simple recurrence analysis of the100 year record (Camilloni and Barros, 2000). 6. Selected Relevant Studies with Numerical Models 6.1 Atmospheric General Circulation Models (AGCMs) Atmospheric general circulation models (AGCMs) refer to numerical models that simulate the evolution, maintenance and variations of the general circulation of the atmosphere. A comprehensive numerical model of the atmosphere can be used either as a AGCM or as an extended numerical weather prediction (NWP) model. The dependence of the solution on initial conditions is usually not emphasized in AGCM applications, as in climate simulations or climate predictions of the second kind, while it is crucially important in NWP applications, or climate predictions of the first kind. AGCMs have been used to estimate regional moisture budgets. According to the moisture budgets by an AGCM in different regions of South America, by Lenters and Cook (1997), suggest that precipitation in the central Andes is primarily associated with orographic effects and large scale wind convergence. Over the SACZ, in contrast, evaporation, wind convergence and moisture advection make positive contributions to the balance, while orographic influences make a negative contribution and transients have a minimum impact. The AGCM simulations, however, do not capture the precipitation maximum in southern Brazil/northeastern Argentina, which corresponds to the SALLJ exit region. Experiments with and without orographic elevations using the same AGCM confirmed the important role played by the Andes in organizing the low-level convergence and precipitation in the region (Tanajura, 1996 Lenters and Cook, 1999). 6.2 Mesoscale models It is apparent that simulations by AGCMs with relatively low-resolution cannot capture crucial local aspects of moisture fluxes and their convergence. This has motivated the use of ensembles of short-range forecasts performed with regional models to estimate moisture budgets in river basins. The consensus view is that such a procedure is the only one that can currently produce reliable results (Berbery and Rasmusson, 1999). The National Centers for Environmental Prediction (NCEP) Eta model (Mesinger et al. 1988) appears to be well suited to represent the sharp slopes of major mountain ranges. Even for a horizontal resolution of 80 km, the eta-model topography (with heights up to 5100 m) captures the massive block of the Andes mountains and the sharp slopes that in some regions become practically vertical walls. Other features, such as the Altiplano, the Brazilian Plateau, and the even smaller Guiana Highlands are also well captured. The role of different processes participating in the moisture budget of the Plata Basin has been investigated by performing a series of forecasts using the Eta model with NCEP/NCAR reanalyses as initial and boundary conditions. (Berbery et al. 1996 Berbery and Collini, 2000). For the southern summer, the model successfully simulated the precipitation maxima over the SACZ, northeastern Argentina/Paraguay/southern Brazil, and southern Chile (see Fig. 8). The importance of the SALLJ in transporting moisture to higher latitudes is apparent in the upper panel of Fig. 9, which depicts the vertically integrated moisture flux as calculated in the models computational grid. The exit region of the low-level jet coincides with a large area of moisture flux convergence collocated with the maximum in precipitation. Consistent with water balance concepts, the results suggest that moisture flux convergence related to the low-level jet is a key component in the processes that generate precipitation over northern Argentina, southern Brazil, and northern Uruguay (lower panel of Fig. 9). 6.3 Hydrological models Hydrological models of river basins can be broadly divided into two types: (a) deterministic, and (b) statistical. Deterministic models seek to describe the relation between precipitation, evaporation and river-flow in physical terms. The river basin may be regarded as a single entity transforming mean precipitation, over the entire basin area, into runoff (a lumped model), or as a set of separate but inter-connected sub-basins which function in series or in parallel (a distributed model). In either case, the model consists of a set of hypothetical reservoirs with rules - often containing empirical constants - which determine how water is transferred between them and/or back to the atmosphere as evaporation losses. Water leaving the reservoirs may be routed along river channels to the exit point of the river basin this routing procedure may involve empirical constants to give the appropriate delay before the output from a reservoir arrives at the basin outfall, or it may use simplified forms of the energy conservation equation. A deterministic model of any type contains parameters which must be estimated. Some parameters can be related to physically measurable quantitites, like soil depths. Others must be fitted by minimizing some measure of difference between modeled streamflow and observed streamflow, either heuristically or via formalized optimization procedures. Deterministic models are useful for making short-term predictions of river behavior (for example, flood routing) and also for giving qualitative estimates of how flow characteristics may change as a result of changes in soil cover. The latter application is limited by the fact that empirical constants fitted by optimization are those giving best fit to the observed (historic) record, and may not be appropriate where conditions of climate or soil cover have changed. Figure 8. Eta model forecast precipitation and three observed estimates. Figure 9. Vertical-mean moisture flux and its convergence simulated by the ETA model. A deterministic model of the Plata Basin must be capable of describing (a) the flooding and subsequent drying out of large areas with relatively shallow gradients through processes of evaporation and infiltration (b) the hydraulic interconnections between such areas. In such models, drainage basin behavior is represented by two kinds of elements: channels and cells. Channels are elements where flow is mainly concentrated and can be considered as one-dimensional (in the direction of channel flow). Water movement in channels is comparatively rapid, and dynamic effects are important. Less rapid flows occur across channel banks, to and from cells adjacent to the channels. Flow in cells can be in any direction, provided there is another cell, or a channel, into which the flow can pass. Flow in cells is considerably slower than in channels because of mild gradients and dense vegetation the most important effect is storage, which increases or decreases water level, and these changes in their turn control water exchange between cells and channels. Cell behavior can be described by a combination of volume balance within the cell and simple hydraulic laws relating each cell to its adjacent cells, channels or boundaries. More recently, so-called macroscale hydrological models, which are designed to represent the hydrological as well as energy fluxes within large continental river basins, have been developed (see, e. g. Wood, 1991 Nijssen et al, 1997). In contrast to the bottom up approach traditionally used for implementation of hydrological models, in which models are implemented and tested for each of a number of tributary subcatchments, macroscale models start with the entire watershed, and subdivide, usually via a grid mesh and corresponding channel network. Figure 10, for instance, shows the channel connectivity for the Variable Infiltration Capacity (VIC) model (Liang et al, 1994) for the Plata Basin at 1/2 degree spatial resolution, which is about the highest resolution justifiable given the spatial density of historic climate records. Models like VIC contain parameterizations of subgrid variability in soil and vegetation characteristics, as well as precipitation, temperature, and other model forcings. Macroscale hydrological models have been particularly useful for assessing the effects of historic and possible future changes in climate and vegetation (Matheussen et al. 2000 Nijssen et al, 2001a), as well as for use in seasonal to interannual climate forecasting, where models capable of representing the hydrology of large areas or watersheds are needed (e. g. Wood et al. 1997). Statistical models of river basins do not incorporate knowledge of physical processes (although the parameters that they contain may sometimes be amenable to physical interpretation). The basic tools needed for the statistical modeling of streamflow are those of time-series analysis. The range of statistical models is very wide, and the following are but three examples: (i) auto-regressive moving-average (ARMA) models (univariate or multivariate) of streamflow sequences (ii) ARMA models of streamflow incorporating precipitation as a causative variable (iii) ARMA models driven by other causative variables, such as SSTs. Statistical models are typically used for short-term forecasting, although it is probable that the lead-time for forecasts would be lengthened if predictor variables (SSTs, possibly) were found which showed good correlation with streamflow. Perhaps the principal advantage of statistical models is that they provide measures of the uncertainty in forecasts. Figure 10. Channel connectivity for the Variable Infiltration Capacity (VIC) model In recent years, statistical models for long-memory processes have been the subject of research, and the usefulness of such models for making streamflow predictions in the Plata Basin is a topic that needs to be explored. It would be reasonable (i) to explore whether long-memory models are appropriate for describing the flow characteristics of rivers in the Plata Basin (ii) to explore how predictions given by such models compare with predictions given by models having a sound physical basis. A further point to be considered is that such models can provide measures of the uncertainty in predictions that result from their use. An important limitation of statistical models is that they require relatively long time series for estimation of parameters, and therefore may have difficulty representing the effects of changing climate. 6.4 Watershed models Watershed models simulate the transformation of a series of daily rainfall inputs to the resulting streamflow hydrograph at the basin outlet. Due to the large area of the catchment rainfall-runoff modeling for the entire Plata Basin and its main sub-basins (Paranaacute, Paraguay, Uruguay, Bermejo and Pilcomayo) has only recently been attempted (Nijssen et al. 2001b). As part of a study of global rivers, Nijssen et al applied the VIC model to the Plata Basin at the very coarse spatial resolution of 2 deg longitude x 2 deg latitude, using the Global Precipitation Data Project (GPCP) and other global data sources as forcings, for the period 1979-93. Figure 11. Mean monthly observed and simulated discharge (in m 3 s -1 ) for the Parana River at Corrientes (Simulation period 1980-1993) Figure 11 shows that although the annual mean runoff was reasonably well simulated, the model greatly overestimated the magnitude of the seasonal cycle of streamflow. The likely reason is the absence of a mechanism in the VIC model to represent the effects of surface storage in seasonal flood plains. A more recent version of the model includes explicit representation of the effects of storage in lakes and wetlands, and may resolve this problem. Another major obstacle to rainfall-runoff modeling in the Plata Basin is the lack of readily accessible historical rainfall data for the basin. Although much of this problem is traceable to the absence of long-term networks, some data are potentially available that have yet to be archived electronically, a problem that Platin may be able to resolve. In any event, most attempts at rainfall-runoff modeling have been confined to the smaller sub-basins, and large scale efforts have focused more on dynamic routing in the channel (see subsection 6.5). Among the efforts at hydrological modeling at the sub-basin scale are application of the Hidro-Urfing model to the Laguna I and the Pereira Basins, two sub-basins of the Negro River catchment with a surface area of 13,945 km 2 and 11,354 km 2. respectively. Hidro-Urfing is a lumped conceptual-hydrological model based on the operational Sacramento catchment model developed by the U. S. National Weather Service and the California Department of Water Resources (Burnash et al. 1973, 1995) and the HBV model developed by the Swedish Meteorological and Hydrological Institute (Bergstroumlm 1976,1995). The model can be applied to large basins with small to gently undulating slopes. Daily rainfall and monthly-mean values of potential evapotranspiration are prescribed based on observational data. Calibration performed using precipitation and streamflow from observational data showed an acceptable agreement between computed and observed hydrographs for the major storms, both for the rising and the limbs (Genta et al. 1992 Silveira 1998, 2000). Other studies have been reported for tributaries of the Uruguay, Tietecirc and Iguazuacute Rivers, and for the Paraguay River and one of its tributaries (Tucci, 1991 Tucci and Damiani, 1994 Damiani, 1991). IPH2 is a rainfall-runoff model developed at the Instituto de Pesquisas Hidraacuteulicas (IPH). Like all hydrological models, its basis is the continuity equation. It works by regarding a drainage basin as a series of storage tanks, with rainfall entering at the top, and being split between what is passed back to the atmosphere as evaporation, and what emerges from the basin as runoff (streamflow). Depending on the number of tanks, and the number of parameters controlling the passage of water between them, the model can be made more complex or less so. The IPH2 Model was used to analyze the effects of climate change on the water resources of some Uruguay River tributaries. There have also been studies of the use of rainfall-runoff models on the Iguazuacute River to explore the effects of proposed hydro-electric schemes in a metropolitan region where urban growth is very rapid. The IPH2 Model was also used (Tucci, 1998) to study rainfall-runoff relationships for a set of tributaries of the Iguazuacute River near to Foz de Areia, the first large reservoir of the hydroelectric generating system on this river. The same model, together with a hydrodynamical model of channel flow, was used in a flood analysis of the metropolitan region of Curitiba, the capital of the Brazilian State of Paranaacute (Tucci, 1996). TOPMODEL is a hydrological model that builds in aspects of basin topography (Beven and Kirkby, 1979). The use of TOPMODEL in a 59 km 2 basin of the Corumbataiacute River, which forms part of Tietecirc drainage basin draining to the Paranaacute River, was explored by Schuler et al. (2000). The authors concluded that the model showed good promise for future applications when adapted to local conditions. The Water and Environment Institute of Argentina (INA) has applied watershed models to the lower part of the Iguazuacute basin. They obtained daily river flows by using the U. S. National Weather Service River Forecast System (NWSRFS). This is a lumped input-output parameter model, which is the main tool for streamflow forecast in the US. 6.5 Hydrodynamical models There are operative hydrodynamical models covering the major rivers of the Plata Basin: Plata itself, Paranaacute, and Uruguay. From the hydrodynamical point of view the Plata River behaves as an estuary since water currents are basically controlled by the oceanic tides penetrating through its mouth. Though the tides amplitude is small (about 0,60 m between low and high tide), the very large river width (minimum 40 km) allows for a tidal prism important enough to dominate the flow regime despite the huge discharge received from the tributaries (average 22,000 m 3 s -1 ). The base flow generated by this discharge is strong enough to avoid saline water penetration in the inner river, extending from its head to the upstream of the imaginary line Punta Piedras (Argentina) - Montevideo (Uruguay). The Platas denomination as a river, instead of as an estuary, arises precisely from this freshwater character. The saline stratification can be detected in the outer region, though complete vertical mixing can occur for strong wind conditions. The Plata River has been modeled as a shallow water body. Shallow-water models are good enough for engineering applications, mainly to provide boundary conditions for nested, local hydrodynamical models to be used in coastal engineering studies. At the present time, groups in Argentina, Uruguay and Brazil have development efforts on three-dimensional hydrodynamical models for the estuary and adjacent shelf waters. The Plata River dynamics and its environment are strongly affected by the variability of its tributary rivers. Salinity structure and distribution and accompanying processes, like sedimentation and ecosystem metabolism, are modulated in such a way that provokes, among other effects, changes in mean sea level mainly in the northern coast. Fisheries in the area, which are a significant economic resource, are affected due to the sensitivity of commercial species to changes in the position of the saline front in the river which controls the spawning and fish recruitment. Efforts to model the Paranaacute River have focused primarily in flood routing problems. One-dimensional models of different stretches of the river have been developed since the seventies for hydraulic engineering studies (Jaime and Meneacutendez, 1997). In addition, a model of the Paranaacute River Delta has been developed and is used in operational mode (Fontana, 1995). The major concern with the Uruguay River in Argentina and Uruguay is flood routing. There have been several attempts to model the river with one-dimensional hydrodynamical models. The Comisioacuten Teacutecnica Mixta (CTM) in charge of the Salto Grande dam, has been operating a hydrodynamical model within an integrated monitoring/hydrological/hydrodynamical model system that assists in water management decisions. The model developed by DPHER for the Paranaacute Delta also includes the Uruguay Rivers stretch from the Salto Grande dam down to the rivers discharge in the Plata River. CARU (the bi-national commission that manages the Uruguay River) has another hydrodynamical model (based on MIKE 11) that is being operated by INA and DNH (Uruguay). Flood behavior in the Paraguay River, particularly in areas subject to frequent seasonal flooding has been studied by Mascarenhas and Miguez (1994) using a hydrodynamical model, coupled with a cell model, to study the authors used their model to describe the formation and passage downstream of floods originating within the Pantanal. In the Planalto region adjacent to the Pantanal, Colischonn et al. (2001) applied a distributed rainfall-runoff model, specifically developed for modeling large basins. The model was used on the basin of the Taquari River, a tributary of the Paraguay that joins it in the Pantanal. Its drainage area above this point is approximately 28 000 km 2. The distributed model has regular square cells of 100 km 2 which are sub-divided into blocks according to soil use and vegetation cover. Despite the limited rainfall records available, it was possible to model a flow sequence with reasonable precision, notably for monthly time intervals. 7.1 Climate and weather prediction Past experience in weather and seasonal climate prediction based on the Center for Ocean-Land-Atmosphere (COLA) model at CPTEC, Brazil, suggests that the regions with highest predictability in South America east of the Andes are northern Amazonia-Northeast Brazil and the extreme southern Brazil-northern Argentina. Central-southeast Brazil (where most of the Paranaacute Basin is located) predictability is relatively low. Here the transition between regimes of convection in Amazonia and the SACZ makes the ENSO signal less clear than in northeast Brazil. For this reason, local correlations between rainfall tend to be low. In addition, it is difficult to define a peak of the rainy season in this season. Similar results have been obtained with the CCM3, the ECHAM and NCEP models. The predictability of hydrological parameters has also been studies using statistical techniques. A system for hydrometeorological forecasts in the seasonal-to-interannual range was developed by Liu et al. (1997) and Valdeacutes et al. (1999). The key features of this system are: 1) multiple ENSO forecasts are integrated into one forecast, 2) each ENSO forecast is weighted according to its error covariance structure as a function of lead-time, and 3) both ENSO and seasonal hydrological forecasts are used to update the underlying persistence (markovian) stochastic process. The system, which produced promising results for the stremflow anomalies of the Nare and Grande Rivers in Colombia, was applied to seasonal forecasts of the Paranaacute River at Corrientes (Valdeacutes et al. 1999). Preliminary results show a weak negative correlation between runoff and the SOI (Aceituno, 1988). This relationship, furthermore, is clearer during low SOI episodes (Garciacutea and Vargas, 1998 Garciacutea, 1999). A sample of the results is given in Table 4. Valdeacutes et al. (1999) also found a clear seasonality of forecasting skills. Similar results were obtained for the streamflows of the Paranaacute at Posadas and the Paraguay at Puerto Bermejo. Table 4 RMSE (root-mean-square-error) reductions (in parenthesis) of seasonal streamflows for the Paranaacute River Interannual-to-decadal predictability of the Paranaacute River has been investigated by Robertson et al. (2001), based upon extracting near-cyclic components in summer-season streamflows at Corrientes over the period 1904-1997. These variations explain about 15 of the variance each for the near 9-year and 15-17 year cycles, compared to about 25 for ENSO. It was found that oscillatory components with periods of about 2-5, 8 and 17 years are accompanied by statistically significant changes in monthly streamflow. Autoregressive predictive models were then constructed for each component (Keppenne and Ghil, 1992). Cross-validated categorical hindcasts based on the 8-yr predicted component were found to yield some skill up to four years in advance for below-average flows no skill is found for above-average flows. A prediction based upon the 8- and 17-yr oscillatory components, including data up to austral summer 1999, suggests increased probability of below-average flows until 2006. The strongest discharges of the Paranaacute River during the fall and winter of the El Nintildeo and SST anomalies in Nintildeo-3 region have a Spearman rank correlation of 0.69 significant at the 95 level (Camilloni and Barros, 2000). This result together with those described in section 5b indicate that there is useful predictability from some months in advance. Care is needed, however, with long-term predictions based on river flow. Although runoff integrates effects of climate change over a drainage basin, it is also affected by land-use change, and it is known (Bruijnzeel, 1996 Sahin and Hall, 1996) that deforestation - which has been widespread in some parts of the Plata Basin - often results in runoff increases. Moreover, annual runoff is not measured directly, but is estimated by means of a calibration curve (rating curve) from which river discharge is estimated, given daily observations of water level in the river (e. g. Mosley and McKerchar, 1993). Because of sediment deposition and/or erosion in river channels as a consequence of deforestation, the rating curve may change with time, and requires constant scrutiny and, if necessary, adjustment. Even without complications arising from land-use change, the uncertainty in the annual flow in the river Paranaacute at Corrientes has been estimated as roughly equal to the annual flow in the River Thames (Clarke et al. 2000). For the Amazon at Oacutebidos, the uncertainty in annual runoff is about equal to the annual flow in the Rhine. Figure 12. The RCs 1--2 and 3--4 computed over 1904-94, plotted 1980-99, together with their predictions made from 1999. (a) Individual RC sums and their predictions, and (b) combined sum (thick solid line) and prediction (stars), together with the raw January-March flow anomalies (thin line). The thin dotted curves in panel (b) show four predictions starting in1995, 1996, 1997 and 1998 respectively. Units: 10 3 m 3 s -1 . 8. Sensitivity to Climate Change Studies of climate change over particular regions of the world are particularly challenging. One possible strategy is to obtain different scenarios from the output of GCM simulations with current and doubled CO 2 concentrations (a word of caution is needed, since models still not consistent with each other and regional precipitation is not completely well simulated for present climate.) This approach was used to assess the impact of climate change on the Uruguay River Basin by Tucci and Damiani (1994). Specifically, they took the percentage increase of temperature and rainfall from simulations with the OS NASA Goddard Institute for Space Sciences (GISS), US NOAA Geophysical Fluid Dynamics Laboratory (GFDL), and the United Kingdom Meteorological Office (UKMO). These were transformed into streamflow anomalies by application of a watershed model. Not unexpectedly, different model produced different results. The GISS scenario represents a reduction in the maximum and annual mean streamflow of 9-14, implying a reduction in energy generation of about 5, although streamflow increases in February-March. GFDLs scenario represents an increase of 14-33, with the largest increase in October. This is interesting, since such an increase would be consistent with warmer SSTs in the tropical Pacific at a time of the year when connections with the climate in southeastern South America are strongest. The increase implies an increase in energy generation of 17. The UKMOs scenario represents increases of 5-21. Minimum streamflows would decrease in all cases. Tucci and Clarke (1998) examined important developments with potential environmental impacts on the Plata Basin: 1) installation of several hydropower reservoirs in the Upper Paranaacute River, in Brazil, from 1960-90 2) deforestation in the Paranaacute, Uruguay and Paraguay basins from 1950-90 3) introduction of intensive agricultural practice after 1970 4) urban developments with change to flood regimes and (5) navigation and conservation of the Upper Paraguay River. Flow increases since 1970 may have been caused by changes in vegetation cover or climate variations, which raises important questions on both water resource development and environmental conservation. Tucci et al. (1999) discussed water management and environmental issues taking account of climate patterns and the development of the five countries sharing the basin. They concluded that rainfall and land-use changes have both contributed to cause the flow increase, although there is not yet a clear answer as to the relative magnitudes of the two contributory causes. Climate variability (both local and remote) can influence the water level, salinity and suspended sediment distribution in the Plata River . Water level rising and turbidity and salinity fronts displacements correlate with climate induced anomalies on tributary rivers flows. The (Paranaacute and Uruguay) river flows can have a distinct impact on the Plata River. The observation indicates that turbidity and salinity fronts displacements on the northern coast correlate with Uruguay River flow. 9. Environmental Issues Understanding the interplay between the natural environment and human activity is critical for sustainable resource management in the Plata Basin. Two major environmental issues are soil erosion and deposition, and the Paranaacute-Paraguay waterway. The degradation of land by agriculture in northwestern Argentina in steepest terrain is generating increasing amounts of sediments that cause difficulties for the navigation in the lower Paranaacute River. The Paranaacute and its tributaries are increasingly polluted by industrial sources along their margins. Also, the increment of navigation as the Hydroway Project progresses may increase the risks of pollution by agro-chemicals. Particularly in the Brazilian Planalto, there has been a dramatic increase since the 1970s in the area planted to annual crops such as soya. Intensive cultivation and the use of heavy machinery have resulted in greatly increased soil erosion and sediment transport to the Pantanal, whilst within this wetland the increase in cattle production disturbs soil that is then transported by water. Sediment is then deposited where the capacity for channel conveyance is reduced. The Paranaacute-Paraguay Waterway Project (Hidrovia Paraguay-Paranaacute) is a 3,600 km long channel, running from Nueva Palmital near the coast of Argentina to a point upstream of Caacuteceres in Brazil. To increase the capacity for transport of agricultural and other products to and from the center of the sub-continent, works are planned that would deepen and straighten sections of the channel the effects of such works on the Pantanal are therefore of major concern. Works to improve river conveyance are likely to decrease flooded areas, which may change the Pantanal from wetland to savannah, since the difference between rainfall and potential evaporation is negative. Two critical questions are therefore: will the proposed works modify flow conditions so as to reduce flow volumes entering the floodplain, and if so, by how much will it be reduced What would be the effect on the flood-plain environment of a sequence of drought years Economic development in the basin can be seen as an outgrowth of the Treaty of the Plata Basin. Signed in 1969, the treaty created a mechanism for integrated development amongst the basin states and instituted the Intergovernmental Coordinating Committee of the Plata Basin Countries (CIC), a mechanism for the coordination of multinational initiatives. Unfortunately, population growth, increased urbanization, intensive agricultural practices, and growing energy demands, coupled with the economic crisis of the 1980s, has led to the unsustainable development of natural capital within the basin. The impacts associated with this development are 1) deforestation and the erosion of productive land, 2) silting of waterways and reservoirs, 3) soil and water pollution, 4) increased risk resulting from natural hazards (i. e. floods and droughts), and 5) loss of biodiversity (Tucci and Clarke, 1998). The following sections provide an overview of the major environmental issues at work in the basin and highlight points of intersection between socioeconomic and environmental processes. 9.1 Land-cover change, deforestation and agricultural production Changes in land-cover, whether they are the result of environmental change or human activity, affect the volume, timing and quality of water available to catchment regions. These changes are the result of complex feedbacks between climate, hydrology, vegetation, and management. Ample evidence exists for land-cover change in the Upper Paranaacute, Paraguay and Uruguay River basins, with the most notable being a 28 increase in Paranaacute River flow since 1970. Tucci and Clarke (1998) note that this increase in river flow occurred after large areas of land had undergone deforestation and/or land-use change. The intensification of agricultural and industrial production led to a transition from coffee to soybeans and sugarcane in the Upper Paranaacute Basin. Soy, unlike coffee, is an annual crop and requires machine-intensive soil preparation. River flow increases also occurred in the Iguazuacute River Basin, a basin that has undergone little, if any, land-use change over the past several decades (Garciacutea and Vargas, 1998). Forested areas were cleared as result of the need for increased crops and pastures in both the Brazilian and Paraguayan drainage areas of the Paraguay River Basin. In response to demand for increased employment and revenue, the Government of Paraguay in the 1960s expanded agricultural production in the Paraguay and Paranaacute River Basins. Forested area, originally covering 45 of eastern Paraguay, decreased to 15 at the beginning of the 1990s (Bozzano and Weik, 1992). Tucci and Clarke (1998) report decreases in forested area in the Paranaacute Basin from 90 in 1952 down to 17 in 1985 and annual crops increased from 0 in 1963 to 58 in 1985. These large changes in hydrological regimes have had significant implications for water resources in both river basins and they raise a number of questions for understanding the links between land-use change and water resources, which are raised in Section 10. 9.2 Increased urbanization: Natural hazards and vulnerability The population of the Plata Basin has grown from 61 million in 1968 to 116 million in 1994, with most people concentrated in small and intermediate cities lacking basic economic and social infrastructure. Population growth, in combination with expansion of the agricultural frontier and the implementation of large-scale energy projects, has led to increased vulnerability. It is anticipated that the most significant environmental problems confronting the Plata Basin countries in the future will come as a result of increased urbanization. 9.3 Critical regions for sustainable development A number of distinct sub-regions of the Plata Basin face critical sustainable management problems (Cordeiro, 1999). They include: the Upper Paraguay, Pilcomayo, Bermejo River Basins, the Chaco region, and the Mirim Lagoon Basin. Here we briefly outline some critical environmental issues confronting the Upper Paraguay River Basin and, specifically, the region known as Pantanal (Wetland). The Pantanal is the most extensive wetland ecosystem in the world, and home to a rich array of wildlife: more than 230 species of fishes, 80 species of mammals, 50 species of reptiles, and more than 650 classified species of aquatic birds. The Pantanal is famously flat, covers an area that can vary from about 10,000 to 140,000 km 2. and behaves like a reservoir retaining a significant portion of the total annual runoff. The primary economy of the Pantanal has been driven by livestock production. In addition to this, manganese reserves are estimated at 100 million tons, iron ore reserves are estimated at 800 million tons. Areas of growth include copper, peat, lignite, gypsum, sapphires, amethysts, and topaz deposits. Minerals presently being exploited include gold, diamonds, limestone, marble, and clay. Since the mid-1970s, the traditional balance between agriculture and mining has been upset due to the expansion of the agricultural frontier in the upper sub-basin as mentioned in Section 9.2. The principal factors causing environmental problems in this sub-basin are soil erosion, caused mainly by production of soybeans and rice, and water pollution caused by the intensive use of agrochemicals and urban and industrial discharges. Soil erosion rates have been estimated at 300 tons km -2 year -1 in the upper sub-basin and at 40 tons km -2 year -1 in the lower basin. Overfishing and the dumping of hazardous chemicals, specifically large quantities of mercury used in gold mining, threaten fish populations. Associated with these existing problems are the potential impacts of ongoing development projects, including the Paraguay-Paranaacute Waterway Project. 10. Applications of Climate Forecasts: Case Studies 10.1 Application of Climate Forecasts to Water Resource Management: a case study of Itaipu Hydropower facilities such as Itaipuacute, on the Paranaacute River are staffed by engineers whose primary goal is optimizing the problem of flood protection vs. energy generation. In the event of predictions of flood, reservoir managers must decide to what extent they will increase reservoir releases to safely accommodate incoming floodwaters. Inherent to this decision process are potential tradeoffs. An underestimation of flood volume leaves the reservoir system unable to fully regulate flow and results in water being discarded into spillways. This suboptimal choice incurs two types of losses: (i) environmental damage due to flooding, and (ii) financial loss due to decreased generating capacity. Financial losses can vary on the order of several million dollars per year. However, if reservoir operators overestimate the upcoming flood and draw their reservoir down too far, flood damage is avoided, resulting in another suboptimal choice with: (i) decreased hydropower output due to reduced hydraulic head on power turbines, and (ii) less water is available for other uses such as public water supply. For these reasons, reservoir operators have a clear need for inflow forecasting given the caveats inherent in forecast uncertainty. Itaipu beat its own production record in 2000, generating a total of 93.4 million MWh, a 3.8 increase from 1999. This represents 84.4 of the stations theoretical maximum, allowing zero downtime. Engineers believe that even an increase in efficiency of only 2-3 resulting from the successful implementation of climate forecast information would provide a significant gain in power and water for irrigation and public use. 10.2 Application of Climate Forecasts to Agriculture: a case study in Uruguay Crop and pasture production in Uruguay is characterized by technologically advanced producers managing relatively large areas with low to medium intensity against the background of high climatic variability. The lack of subsidies combined with low commodity prices requires producers to become increasingly efficient. The impact of climate variability in Southeastern South America, which includes Uruguay, (see subsection 4.4) led to the establishment of pilot programs that bring together climate scientists, agronomists, crop modelers and farmer representatives. Supported by organizations such as NOAA (OGP), IRI, IAI and regional association of farmers, these groups participate in the Regional Climate Outlook Fora for South East South America. Uruguay hosted the first Forum in December 1997, and fora have been uninterruptedly organized in the region every 3-4 months. For the scientists involved these fora provide an excellent opportunity to interact, exchange results, discuss methodology, and obtain feedback from producers about the general approach, the methodologies used and additional information needs. In 1999 the regional office of IFDC (International Fertilizer Development Center) in South East South America established collaborative activities with researchers from INIA (National Agricultural Research Institute, Uruguay) and NASA GISS to develop tools for optimizing the use of the climate outlooks (Baethgen and Magrin, 2000 Meinke et al. 2001). Activities include: (i) Identify crop or pasture systems that have a good signal of ENSO, i. e. where the underlying climatic fluctuations translate into associated fluctuations of production (e. g. Messina et al. 1999), (ii) Identify climate variables that explain a large proportion of the observed production variability (e. g. rainfall around flowering in maize, late frosts in wheat, soil water availability in rangelands), (iii) Use crop and pasture simulation models to explore management practices that can minimize losses or take advantage of favorable conditions associated with expected climate anomalies. Also, use the information to produce crop/pasture productivity forecasts, and (iv) Introduce these components in the Information and Decision Support Systems currently being developed for the region (Baethgen et al. 2000). Short workshops are then conducted that include the climate scientists from the University of Uruguay, agricultural researchers (INIA and IFDC) and technical representatives of all the major farmer associations and government agricultural planners (Ministry of Agriculture and Fisheries). In these workshops, climate scientists present the outlook form the regional fora, as well as local experimental forecasts (which have higher spatial resolution) developed by the University climate research groups. The agronomists and modelers present results on the impact of climate variables on production under a range of different management scenarios (what if analyses). Finally, and most importantly, the technical representatives from the farmer associations critique the scientists work by providing feedback and suggesting alterations or modifications for the preliminary analyses conducted. The technical representatives will brief their associations on the final outcome. In addition, short documents for the press are prepared (newspapers, radio and TV). Finally, annual workshops for the press are planned, since that is still the major source of information for the farmers in this region. Similar activities are taking place in neighboring Argentina (G. Magrin, INTA, pers. comm. 1999) and in southern Brazil (G. Cunha, EMBRAPA, pers. comm. 2001) and the regional fora are playing an important role in facilitating cross-border collaboration. The original program in Uruguay was developed in response to the considerable press coverage of ENSO-related climate variability, particularly after the 1997-98 El Nintildeo event. Many people (often not scientists) with good access to the press were covering the subject and many forecasts were being disseminated, often contradicting each other. This resulted in much confusion and concern in the agricultural sector, since people could not tell which source was credible. The regional forum of December 1997 organized in Uruguay was extensively covered by the press and demonstrated to the agricultural sector of this region that there are scientifically sound approaches and people capable of conducting serious and useful work available. This program in Uruguay is an excellent illustration of both the successes and the constraints for applying seasonal climate forecasts in the agricultural sector. On the one hand, policy makers have actually started to use information produced in the research program to respond to extreme events (testimonies from the Minister of Agriculture and Fisheries and from the National System for Emergencies in Uruguay can be found in inia. org. uy/disciplinas/agroclima/index. html. under Testimonios). On the other hand, farmers and other users are commonly finding difficult to effectively use the information of currently available seasonal climate forecasts to make better decisions and improve their planning. Thus, the programs research activities have increased the users awareness of the potential uses for climate outlooks but have also intensified the demand for better seasonal forecasts. 10.3 Application of Climate Forecasts to Urbanization: a case study in Buenos Aires The application of climate forecasts to the management and solution of urban problems has had a limited impact in Argentina. Users in this country receive daily information on weather forecasts and, to a certain extent, on seasonal forecasts as well. However, such information is received with some skepticism, since forecasts are not perfect. At the same time, the Government has not implemented actions to include climatic and meteorological information in the context of a social communication process, which is broader and more complex than the simple distribution of climatological data. Finally, the collection and elaboration of basic climatological data is not a priority in the governmental agenda. The difficulties emerging from the situation described above become evident in the analysis of the catastrophic floods produced in the last decades (1983 to present) in the fluvial littoral of the lower Plata Basin, where floods are the most important hazard among environmental risks. Such analysis has been performed for cities of intermediate size (Zaacuterate and Campana in the province of Buenos Aires) and a large city (Buenos Aires) (Natenzon et. al . . 2001) Zaacuterate and Campana have approximately 100.000 inhabitants each. Here, flood management was analyzed especially in the context of the early warning system (Gentile, 1999). Floods in these cities have three main causes: 1) overflows of the Paranaacute river, 2) in situ rains, and 3) effects of sudestadas. (Sudestadas are hydro-meteorological situations in which persistent winds from the southeast produce the flood of the eastern coast of the Plata River.) The technical component of the Warning System (INA) proved to work properly. With the information of the situation in the upper basin, it is possible to forecast a flood approximately 30 days in advance. The warning message reaches the cities through the offices of Civil Defense and the Argentinean Coastguard. The Civil Defense officer is responsible for disseminating the information to community organizations in flood prone neighborhoods, which in turn inform the affected neighbors. The Coastguard disseminates the warning to the population in the islands of the Delta. Despite this communication system, individuals get the first warning through the mass media, which inform of floods in the upper basin, rather than through the local communication channels. In case of floods due to local intense rains, there are meteorological warnings, but they have some deficiencies in the quality of information and in the anticipation timing. Buenos Aires has about 3 million inhabitants. Here, the problem is more complex due to the difficulty to predict with precision the locations where rainstorms would cause the floods. Floods in Buenos Aires have two origins: intense rainstorms and sudestadas . Intense rainstorms cause the overflow of obsolete drainage systems (built at the beginning of the 20th century) without enough capacity to drain rains concentrated in a brief period of time. The sudestada prevents the streams that cross the city to discharge their waters in the Plata River (Barrenechea et. al. in press). Intense rainstorms warnings are launched with very small anticipation, which hampers decision-making during emergencies. Accurate forecasts require a network of meteorological stations that provides a more complete coverage than that currently available. In the case of sudestadas . the tide gauge network of the Argentinean Navy Hydrographic Service-SHN allows an anticipation of about 12 to 24 hours. The combination of both situations - storms and sudestada - results in the maximum risk hypothesis, which may have serious impacts in spite of its low recurrence. In any event, data collection is only an aspect of the problem. It would be desirable to include in the warning message some information of simple measures that population should follow before, during and after the potential flood so as to lower the impacts. The present warning system does not seem to be integrated warning messages are generally very vague and do not include information on what people must do. Only in the current year -2001- the government of the city has started to broadcast frequent warnings during TV and radio programs advising individuals on actions to take in case of flood (Gentile, 2000 Gonzaacutelez, 2000). In summary, information is scarce and a more sophisticated system of data collection should be implemented. But even in the present situation, all potential users do not employ the existing information in an integrated manner during the whole disaster cycle. 11. Motivation for an International Program on the Plata Basin The review of climatology and hydrology of the Plata Basin presented in this document highlights the need for an international research program that targets three major topics of principal interest to countries in the basin: middot What climatological and hydrological factors determine the frequency of occurrence and spatial extent of floods and droughts middot How predictable is the regional weather and climate variability and its impact on hydrological, agricultural and social systems of the basin middot What are the impacts of global climate change and land use change on regional weather, climate, hydrology and agriculture Can their impacts be predicted, at least in part To properly answer these questions a number of issues on the climatology and hydrology of the Plata Basin should be addressed. 1. To what degree is the basin climatology and hydrology affected by SST anomalies Conversely, how do the larger scale precipitation and surface winds affect the nearby oceanic circulation Does the SACZ play an active role, or is it merely responding passively to large-scale changes 2. How is decadal variability in the tropical Atlantic SSTs linked to precipitation anomalies in the basin, particularly in the northern part (Upper Paraguay and Paranaacute, Upper Bermejo and Pilcomayo) 3. What are the seasonal variations of the links between anomalies in SST and in climate over the basin 4. What is the relative importance of local and remote sources of moisture in the basin Of the water vapor that enters the basin and falls as precipitation, is any of it recycled within the la Plata basin itself If so, how much, where from, and where does it fall 5. Do soil processes play an important role in the basin In particular, do the large variations in the flooded area of the Pantanal impact and one themselves influenced by the variations in region climatology Does water evaporated from the Pantanal wetland fall as precipitation elsewhere within the Plata Basin If so, how much is recycled, and where does it fall 6. There are proposals to extend the navigable waterways of the Plata-Paraguay River system, by deepening and straightening parts of the channels. This is likely to accelerate drainage from the Pantanal, with consequent effects on the spatial extent of seasonal flooding. How would this affect evaporation from the Pantanal, and (see previous question) how would it affect precipitation elsewhere within the Plata Basin Also, if the channel works are carried out, what would be the consequences for (a) flood frequency and magnitude, (b) duration and severity of drought, elsewhere within the basin 7. If the spatial and temporal extent of flooded areas in the Patanal are changed as a consequence of channel works, what will be the consequences in terms of quantities of sediment removed by runoff If the basins sediment yield is increased, where will the transported sediment be deposited, and what will be the consequences for hydropower production, river navigation, and water supply 8. What determines the near-cyclic variations in the major rivers of the Plata River Basin (Paranaacute, Paraguay, Uruguay, Negro) 9. Can the links between near-cycles found in SST and streamflow variations be used to obtain useful probabilistic prediction of river behavior 10. What are the climatological and hydrological characterization of droughts and floods in the Plata Basin both in time and space 11. The change from native forest to annual high-value crops, such as soya, is likely to have (a) increased annual runoff (b) affected the magnitudes and frequency of occurrence of floods and low flows in several parts of the basin, and the change in land-use accelerated after 1970. Can the effects of land-use change on annual runoff, flood flows, and low flow duration be separated, in the flow record, from the effects of climate variations 12. What developments and improvements in hydrological models are required to better represent the relationships among model parameters and changes in soil use 13. How predictable is the hydroclimatology variability in the Plata Basin 14. What are the most limiting factors to adequately address these questions 12. Relevance to the World Climate Research Programme (WCRP) The scientific problems in the Plata Basin are highly relevant to WCRP/CLIVAR, which has an emphasis on ocean-atmosphere interactions. They are also highly relevant to WCRP/GEWEX, which ha s an emphasis on land-atmosphere interactions. Within CLIVAR, the Plata Basin is of direct interest to VAMOS, which encourages study programs on a better understanding of the American monsoon systems and their variability. VAMOS also aims to a better understanding of the role of American monsoon systems in the global water cycle, improved observational datasets and improved simulation and monthly-to-seasonal prediction of the monsoon and regional water resources. A particular important field program of VAMOS to be developed in the period 2002-2004 is the American Low-Level Jets (ALLS). The South American component of ALLS targets the low-level jet east of the Andes, which has been presented in this document a major contributor to moisture transports into the basin. 13. Outline of an Implementation Plan Preliminary discussions on the needs to develop an implementation plan are under way. They are based on the fact that the basin is subject to strong teleconnections as well as strong local forcings, hence there is a potential for long range forecasting of runoff in the basin. This entails an improved ability to mitigate effects of floods and droughts, and/or more efficiently management water resources -- with attendant social benefits. An outline of an implementation plan can be based on four components. 13.1 Enhancement climate and hydrology monitoring This component would include the planning of stream gauges as needed, and telemetering implementation of networks of hydrological instruments appropriate for monitoring and prediction in the long term. At the spatial scales for which a climate-based initiative would be relevant, a probable target would be 50-100 stream gauges. Relevant questions are where the existing ones are located and where the holes would be. Also, and quite likely more important, would be enhancement of the precipitation network both with gauges and radar. Additional augmentation of the surface meteorological network, including radiosondes, would also be an element. All of this requires an extensive review of the existing network. 13.2 Development of a data center in the region . This component would be preceded with a data rescue effort. There almost certainly are surface climate data that are not readily available in electronic form, and that would be useful for model implementation (a key part of long-range ensemble hydrological forecasting has to do with correction for bias, which requires construction of the best possible retrospective data sets. In this way, model runs, forced with observations, can be compared with those forced with retrospective climate ensembles, and appropriate mappings made. In the U. S. archival surface station data goes back to 1950 in electronic form, and currently is being extended backward from there. The situation is not as favorable in the Plata Basin. Figure 13. Links between climate variability in the Plata River Basin (area encircled by the red curve) and SST anomalies for the southern warm season (December-February). Green shading corresponds to precipitation (mm/month), black arrows to 925 hPa winds, thick blue arrows to maxima in vertically integrated moisture transport, and the blue hatched region to the Pantanal. The configuration of SST anomalies corresponds to enhanced precipitation in the basin . 13.3 Development of regional climate and hydrological prediction centers in the basin. This component would aim to utilize the climate forecasting capability (to be implemented at an appropriate location within one or more of the participaing countries) to perform ensemble streamflow forecasts over the basin (and in particular, at selected gaged locations). Tasks would involve implementing a macroscale, presumably grid based (like VIC, NOAH, or similar) hydrological model, run to forecast time with observations, and subsequently out to (say 6 months to a year) ensemble climate forecasts. Because of the close link between the climate and hydrological foreasting, it makes sense to co-locate these activities, although that may not need to be explicitly stated. Key aspects of the forecast center would be (I) moderate to high resolution ensemble climate forecasts, presumably generated via nesting of a regional model within a global model, run with forecast SST in ensemble mode, (ii) real-time data acquisition, archiving, and handling system capable of extending a (gridded) surface forcing data set (precipitation, temperature, and other surface met variables) to real-time, (iii) a macroscale hydrological model, with interface to the ensemble climate forecasts, and run to forecast time with gridded observations, and (iv) surface data assimilation capability, e. g. for satellite observations, to improve hydrological forecast initial conditions. 13.4 Development of a system for information distribution This component would produce a decision support system (DSS). The DSS would integrate climate and hydropower information with the ability to optimize operational strategies for agriculture, reservoir management, and drought/flooding control. The current consensus is that climate variability in the Plata Basin is influenced by remote climate anomalies, such as SST variability in the Pacific and Atlantic Oceans. Positive precipitation anomalies correspond to warm events in the tropical Pacific. They also correspond to warm SST anomalies in the western South Atlantic, particularly during the southern spring. Furthermore, higher streamflow appears associated with cold SST anomalies in the north tropical Atlantic (see Fig. 10). The mechanisms at work for these connections are not clearly understood at present. The current consensus, in addition, states that the major contribution to the moisture flux into the basin comes through a moisture corridor east of the Andes, at least during the monsoon season. There is also evidence that precipitation in the basin is inversely correlated with the intensity of the SACZ. Much work is requested to quantify these relationships. The climatology and hydrology of the Plata Basin, therefore raises a number of important questions that address key aspects of those scientific disciplines. The answers to those questions have the potential for increased predictability of anomalies since it is becoming increasingly apparent that climatic variability ought to be considered for improvement of water resources management. In the Plata Basin, some of the flood protection works done along the Paranaacute River margin for cities partially located on the flood plain were designed after the 1992 flood. These proved to be inadequate during the 1998 ENSO event when a historical precipitation maximum of extraordinarly high intensity occurred on watersheds discharging on the Middle Paranaacute River. Then, the embankments built to avoid the flood produced by the Paranaacute River acted as a barrier to the discharge from these watersheds. The management of the Salto Grande dam was successful in 1998-1999, on the other hand, because climate information was taken into account. Work will be required, however, to improve hydrological models to be used in support for water resources management at both the operational and strategic levels. Operational management demands short (days) to medium-term (seasonal) forecast. Strategic management, on the other hand, requires the evaluation of scenarios and knowledge of long-term (interseasonal to interdecadal) variability. At this level, the variability of climatological parameters needs to be considered. One challenge to be addressed for the Plata Basin is the downscaling of precipitation produced by climate model forecasts to be used for prediction of water resources. Another is the identification of key variables that couple hydrological and atmospheric processes, e. g. precipitation and actual evapotranspiration. There is also strong interest in assessing the impact of deforestation in the Basin and other anthropic changes of runoff production mechanisms. From the hydrological viewpoint, it is important to evaluate hydrology of flat lands where vertical processes predominate, such as in the lower part of the Basin. A better understanding of the climatology and hydrology of the Plata Basin will have many important benefits. Some will come from the more successful predictions of droughts and floods, which have significant direct and indirect effects on regional economies. The effects on agriculture generally imply the need to allocate funds for goods substitution, additional activities and, in some cases, compensations. The strategic planning at the economical level is strongly affected by such events, and improvement of forecast can be of great help. Flood events in particular have an impact on soil structure and conservation. Large amounts of soil disappear, transported by the rivers. This impact can be more important than the loss of the crop, since the time needed for soil recuperation is larger. These are all topics of great importance to the societies in one of the most populated and fertile regions of the Americas. In view of the magnitude and extent of the problem, a research effort coordinated at the international level is required. The World Climate Research Programme (WCRP) through its CLIVAR and GEWEX components is ideally suited to provide scientific coordination. Acknowledgments. Warm thanks are due to M. Patterson and R. Lawford (NOAA OGP) for their support and encouragement. This document evolved from an earlier version prepared by a study group that met in Montevideo, Uruguay, 9-12 December 1999. The meeting was sponsored by the Asociacioacuten de Universidades Grupo Montevideo (AUGM) and the US National Atmospheric and Oceanic Administration (NOAA PACS and GCIP programs). Contributions to the first version of this document were provided by C. Roberto Mechoso (U. California, Los Angeles), E. Hugo Berbery (U. Maryland), Norberto O. Garciacutea (U. Nacional del Litoral, Argentina), Joseacute L. Genta (U. Repuacuteblica, Uruguay), Carlos Martiacutenez (U. Repuacuteblica, Uruguay), Angel Meneacutendez (INA-Argentina), Mario Nuacutentildeez (U. Buenos Aires, Argentina), Julia N. Paegle (U. Utah, USA), Gabriel Pisciottano (U. Repuacuteblica, Uruguay), Andrew W. Robertson (U. California, Los Angeles, USA), Luis Silveira (U. Repuacuteblica, Uruguay), Carlos E. M. Tucci (U. Federal Rio Grande do Sul, Brazil), Juan Valdes (U. Arizona, USA). E. H. Berbery coordinated the preparation of this second version. Figures 2, 4, 5, 7, 8, 9 were prepared E. H. Berbery Fig. 3 was provided by M. Doyle and V. Barros Fig. 6 was provided by Angel Menendez Figs. 10 and 11 were provided by D. Lettenmaier and B. Nijssen Fig. 12 was provided by A. W. Robertson. and Fig. 13 was prepared by C. R. Mechoso and E. H. Berbery. I. Chen typed the manuscript. Aceituno P. 1988: On the functioning of the Southern Oscillation in the South American sector. Part 1: Surface Climate. Mon. Wea. Rev . 116 . 505-524. Aceituno, P. and A. Montecinos, 1997: Patterns of convective cloudiness in South America during the austral summer from OLR pentads. Preprints, Fifth Int. Conf. on S. Hemisphere Meteor. and Oceanography . Amer. Meteor. Soc. 328-329. Baethgen W. E. and G. O. Magrin, 2000: Applying Climate Forecasts in the Agricultural Sector: The experience of South East South America. Proceedings of the International Forum on Climate Prediction, Agriculture and Development . April 2000, International Research Institute for Climate Prediction (IRI), Palisades, New York, 38-44. Baethgen, W. E. R. Faria, A. Gimeacutenez, and P. Wilkens. 2000: Information and decision support systems for the agricultural sector. Proceedings of the International Symposium on Systems Approaches for Agricultural Development . SAAD. Lima, Peru. Barrenechea, J. E. Gentile, S. Gonzaacutelez, and C. E. Natenzon (in press) Riesgos en Buenos Aires. En: Desastres y Sociedad. Lima, LA RED. Barros, V. and M. Doyle, 1996: Precipitation trends in Southern South America to the east of the Andes. Center for Ocean-Land-Atmosphere Studies. Report Ndeg 26. Editors J. l. Kinter III and E. K. Schneider. pp. 76-80 Barros V. M. Gonzalez, B. Lliebmann, and I. Camilloni, 2000a: Influence of the South Atlantic sea surface temperature on interannual summer rainfall variability in Southeastern South America. Theor. Appl. Climatol . 67 . 123-133 Barros, V. R, M. E. Castantildeeda, and M. E. Doyle, 2000b: Recent precipitation trends in Southern South America east of the Andes: an indication of climatic variability. In: P. P. Smolka, W. Volkheimer (Eds.) Southern Hemisphere paleo - and neoclimates. Springer-Verlag Berlin Heidelberg New York, pp 187-206. Berbery, E. H. E. M. Rasmusson, and K. E. Mitchell, 1996: Studies of North American Continental-scale Hydrology using ETA Model Forecast Products. J. Geophys. Res. . 101 . 7305-7319. Berbery, E. H. and E. M. Rasmusson, 1999: Mississippi moisture budgets on regional scales. Mon. Wea. Rev. . 127 . 2654-2673. Berbery, E. H. and E. A. Collini, 2000: Springtime precipitation and water vapor flux over southeastern South America. Mon. Wea. Rev . 128 . 1328-1346. Bergstroumlm S. 1976: Development and application of a conceptual runoff model for Scandinavian catchments . SMHI (Swedish Meteorological and Hydrological Institute). Reports RHO, No. 7. Norrkoumlping, Sweden. Bergstroumlm, S. 1995: The HBV model. Computer Models of Watershed Hydrology . V. P. Signh, Ed. Water Resources Publication, Colorado, USA. Beven, K. and M. J. Kirkby, 1979: A physically based variable contributing-area model of basin hydrology. Hydrol. Sci. Bull . 24 . 43-69. Bischoff, S. A. N. O. Garciacutea, W. M. Vargas, P. D. Jones and D. Conway, 2000: Climatic variability and Uruguay River flows. Int. Water Res. Association . 25 . 3, 446-456 Biswas, A. K. and Cordeiro, N. V. and Braga, B. P. and Tortajada, C. United Nations University Press, Tokyo, p. 148-174. Bozzano, B. and J. H. Weik, 1992. El Advance de la Deforestacion y el Impacto Economico. Proyecto de Planificacion del Manejo de Recursos Naturales. Asuncion MAG/GP-GTZ. Bruijnzeel, L. A. 1996: Predicting the hydrological impacts of land cover transformation in the humid tropics: the need for integrated research. Amazonian Deforestation and Climate . J. H. C. Gash, C. A. Nobre, J. M. Roberts, R. L. Victoria (Eds) Wiley, Chichester, 611pp. Burnash, R. J. C. R. L. Ferral, and R. A. McGuire, 1973: A generalized streamflow simulation system - conceptual modeling for digital computers. U. S. Department of Commerce, National Weather Service and State of California, Department of Water Resources, California, USA. Burnash, R. J. C. 1995: The NWS River Forecast System Catchment Modeling. Computer Models of Watershed Hydrology . V. P. Signh, Ed. Water Resources Publication, Colorado, USA. Camilloni, I. A. and V. R. Barros, 2000: The Paranaacute river response to El Nintildeo 1982-83 and 1997-98 events. J. Hydrometeorology . 1 . 412-430. Camilloni, I, and M. E. Castantildeeda, 2000: On the change of the annual streamflow cycle of the Paranaacute River. Preprints, Sixth Int. Conf. on S. Hemisphere Meteor. and Oceanography of the Southern Hemisphere. Amer. Meteor. Soc. 294-295 Castantildeeda, M. E. and V. Barros, 1994: Las tendencias de la precipitation en el cono Sur de America al este de los Andes. Meteorologica, Buenos Aires, Argentina, 19(1-2): 23-32. Clarke, R. T. E. M. Mendiondo, L. C. Brusa, 2000: Uncertainty in mean discharge in two large South American rivers due to rating curve variability. Hydrological Sciences Journal . 45 (2) 221-236. Colischonn, W. C. E. M. Tucci, and R. T. Clarke, 2001: Further evidence of changes in the hydrological regime of the River Paraguay: part of a wider phenomenon of climate change Jour. of Hydrology, 245 . 218-238. Cordeiro, N. V. 1999: Environmental Management in Plata Basin in: Management of Latin American river basins: Amazon, Plata, and Sao Francisco, eds. Damiani, A. R. R. 1991 Avaliaccedilatildeo da alteraccedilatildeo do escoamento devido ao efeito estufa na bacia do rio Uruguai. Dissertaccedilatildeo de mestrado IPH UFRGS 191 p. Diaz, A. F. C. D. Studzinski, and C. R. Mechoso, 1998: Relationships between precipitation anomalies in Uruguay and southern Brazil and sea surface temperature in the Pacific and Atlantic oceans. J. Climate . 11 . 251-271. Diacuteaz, E. L. 1959. Fluctuaciones de la continentalidad y en las lluvias. Anal. Soc. Cient. Tom. CLXVII. 73-97. Energy Information Administration: eia. doe. gov Fontana, S. G. 1995: Modelacioacuten matemaacutetica del Delta del Riacuteo Paranaacute - Evaluacioacuten Hidraacuteulica. Direccioacuten de Hidraacuteulica y Recursos Hiacutedricos. Gobierno de Entre Riacuteos. Gan, M. A. and V. B. Rao 1991: Surface cyclogenesis over South America. Mon Wea. Rev . 119 ,1293-1302 Fortune, M. A. and V. E. Kousky, 1983: Two severe freezes in Brazil: Precursor and synoptic evolution. Mon. Wea. Rev . 111 . 181-196. Garciacutea, N. O. and W. M. Vargas, 1998: The temporal climatic variability in the Riacuteo de La Plata basin displayed by the river discharges. Climatic Change . 38 . 359-379. Garciacutea, N. O. 1999: Anaacutelisis de la Variabilidad Climaacutetica de la Cuenca del Riacuteo de la Plata a Traveacutes de los Caudales de sus Principales Rios, Doctoral dissertation, University of Cordoba. Genta, J. L. C. Anido and L. Silveira, 1992: Aplicacioacuten del modelo HIDRO-URFING a la cuenca del Rio Tacuaremboacute. XV Congreso Latinoameriano de Hidraulica. 8-12 September 1992. International Association for Hydraulic Research. Argentina, Colombia, 455-465. Genta, J. L. G. Perez Iribarren, and C. R. Mechoso, 1998: A recent increasing trend in the streamflow of rivers in Southeastern South America. J. Climate . 11 . 2858-2862. Gentile, E. 1999: Gestioacuten social de cataacutestrofes sociales en Argentina: el caso de las inundaciones en las ciudades intermedias del Bajo Paranaacute . Informe final. Beca de Iniciacioacuten, CONICET, periacuteodo 1997-1999. Gentile, E. 2000: La incorporacioacuten de la gestioacuten del riesgo por inundaciones en la gestioacuten urbana puacuteblica. El caso del barrio de La Boca. Encuentro de Investigadores Lo urbano en el pensamiento social . Facultad de Ciencias Sociales-UBA, Instituto Gino Germani. Buenos Aires, 29 y 30 de setiembre. Gonzaacutelez, S. 2000: Gestioacuten urbana puacuteblica y desastres. Inundaciones en la baja cuenca del arroyo Maldonado (Capital Federal, 1945-2000) . Informe final. CONICET - Beca de Formacioacuten de Posgrado, periacuteodo 1998-2000. Grimm, A. M. and P. L. Silva-Dias, 1995: Analysis of tropical-extratropical interactions with influence functions of a barotropic model. J. Atmos. Sci., 52 . 3538-3555. Grimm, A. M. S. E. T. Ferraz, and J. Gomes, 1998: Precipitation anomalies in Southern Brazil associated with El Nintildeo and La Nintildea events. J. Climate, 11, 2863-2880. Grimm, A. M. V. Barros, and M. Doyle, 2000: Climate Variability in Southern South America Associated with El Nintildeo and La Nintildea Events. J. Climate . 13 . 35-58. Hamilton, M. G. and J. R. Tarifa, 1978: Synoptic aspects of a polar outbreak leading to frost in tropical Brazil, July 1972. Mon Wea. Rev . 106 . 1545-1556. Higgins, R. W. J. E. Janowiak, and Y. Yao, 1996: A gridded hourly precipitation data base for the United States (1963-1993). NCEP/Climate Prediction Center ATLAS No. 1, 47 pp. Hoffmann, J. A. 1975: Maps of mean temperature and precipitation. Climatic Atlas of South America. Vol 1 WMO. UNESCO Jaime, P. R. and A. N. Meneacutendez, 1997: Modelo hidrodinaacutemico del riacuteo Paranaacute desde Yacyretaacute hasta la ciudad de Paranaacute. Report LHA-INA 165-01-97. Keppenne, C. L. and M. Ghil, 1992: Adaptive filtering and prediction of the Southern Oscillation index. J. of Geophys. Res. Washington, DC, 97(D18): 20449-20454. Kiladis, G. N. and H. F. Diaz, 1989: Global climatic anomalies associated with extremes in the Southern Oscillation. J. Climate, 2, 1069-1090. Kiladis, G. N. and K. M. Weickmann 1992: Circulation anomalies associated with tropical convection during Northern winter. Mon. Wea. Rev. . 120 . 1900-1923. Lenters, J. and H. Cook, 1997: On the origin of the Bolivian high and related circulation features of the South American Climate. J. Atmos. Sci . 54 . 656-678. Lenters, J. and H. Cook, 1999: Summertime precipitation variability over South America: Role of the large scale circulation. Mon. Wea. Rev . 127 . 409-431. Liang, X. D. P. Lettenmaier, E. F. Wood, and S. J. Burges A Simple Hydrologically Based Model of Land and Energy Fluxes for General Circulation Models, Journal of Geophysical Research . 99(D7), 14, 415-14, 1994. Liebmann, B. G. Kiladis, J. Marengo, T. Ambrizzi, and J. Glick, 1999: Submonthly convective variability over South America and the South Atlantic Convergence Zone. J. Climate . 12. 1877-1891. Liu, Z. J. Valdeacutes, and D. Entekhabi, 1997: Merged forecasts of drought index anomalies along the Gulf Coast in the US using multiple precursons, with a Kalman filter. Experimental Long-Lead Forecast Bulletin . NOAA, 6 . 38-40. Marengo, J. 1995: Variations and change in South American streamflows. Clim. Change . 31 . 99-117. Marengo, J. J. Tomasella, and C. Uvo, 1998: Long-term streamflow and rainfall fluctuations in tropical South America: Amazonia, Eastern Brazil and Northwest Peru. J. Geophys. Res., 103 , 1775-1783 Mascarenhas, F. C. B. Miguez, M. G. 1994 Modelaccedilatildeo de grandes planiacutecies de inundaccedilatildeo por um esquema de ceacutelulas - Aplicaccedilatildeo ao Pantanal de Mato Grosso. RBE Caderno de Recursos Hiacutedricos Volume 12 Nordm 2 Dezembro. Matheussen, B. R. L. Kirschbaum, I. A. Goodman, G. M. ODonnell, and D. P. Lettenmaier, 2000: Effects of Land Cover Change on Streamflow in the Interior Columbia Basin, Hydrological Processes . 14 (5): 867-885. Mechoso, C. and G. Perez-Iribarren, 1992: Streamflow in southeastern South America and the Southern Oscillation. J. Climate . 5 . 1535-1539. Meinke, H. W. E. Baethgen, P. S. Carberry, M. Donatelli, G. L. Hammer, R. Selvaraju, and C. O. Stockle. 2001: Increasing profits and reducing risks in crop production using participatory systems simulation approaches. Agric. Systems (In Press). Mesinger, F. Z. I. Janjicircc, S. Nickovic, D. Garrilov, and D. G. Deaven, 1988: The step-mountain coordinate: Model description and performance for cases of Alpine lee cyclogenesis and for a case of Appalachian redevelopment. Mon. Wea. Rev . 116 . 1493-1518. Messina C. D. J. W. Hansen, and A. J. Hall, 1999: Land allocation conditioned on El Nintildeo Southern Oscillation phases in the Pampas of Argentina. Agric. Systems, 60, 197-212. Minetti, J. L. S. Radicella, M. I. M. de Garciacutea, and J. C. Sal Paz, 1982: La actividad anticicloacutenica y las precipitaciones en Chile y en la zona cordillerana central andina. Rev. Geofiacutesica. IPGH-OEA. Ndeg16, 145-157. Minetti, J. L. and W. M. Vargas, 1983: Comportamiento del borde anticicloacutenico subtropical en Sudameacuterica. I parte. Meteoroloacutegica. Vol. XIV. Ndeg 1-2. Mosely, M. P. and A. I. McKerchar, 1993: Streamflow. Handbook of Hydrology, D. R. Maidment (Editor in Chief), McGraw Hill Inc. Natenzon, C. et al. 2001: Riesgo, cataacutestrofes e incertidumbre. Inundacions y accidentes tecnoloacutegicos en el litroal fluvial de la baja cuenca del Plata. Informe final. Buenos Aires, UBACyT/Agencia/CONCET mimeo. Nijssen, B. E. F. Wood, D. P. Lettenmaier, X. Liang, and S. W. Wetzel, 1997.Streamflow Simulation for Continental-Scale Watersheds, Water Resources Research . 33(4), 711-724. Nijssen, B. G. M. ODonnell, A. F. Hamlet, and D. P. Lettenmaier, 2001a. Hydrologic Sensitivity of Global Rivers to Climate Change, Climatic Change . Nijssen, B. G. M. ODonnell, D. P. Lettenmaier, D. Lohmann, and E. F. Wood, 2001b. Predicting the Discharge of Global Rivers, Journal of Climate . Nogueacutes-Paegle, J. and K. C. Mo, 1997: Alternating wet and dry conditions over South America during summer. J. Atmos. Sci., 125 . 279-291. Nogueacutes-Paegle, J. E. Berbery, 2000: Low-level jets over the Americas. CLIVAR Exchanges . 5 (2), 5-8. Parameter, F. C. 1976: A Southern Hemisphere cold front passage at the equator. Bull. Amer. Meteor. Soc . 57 . 1435-1400. Pentildealba, O. and W. Vargas, 1993: Study of homogeneity of precipitation in a region in the province of Buenos Aires, Argentina. Theor. Appl. Climatol . 47 . 223-229. Pentildealba, O. and W. Vargas, 1996: Climatology of monthly and annual rainfall in Buenos Aires, Argentina. Meteorol. Appl . 3 . 275-282. Pisciottano, G. A. Diaz, G. Cazes, and C. R. Mechoso, 1994: El Nintildeo-Southern Oscillation impact on rainfall in Uruguay. J. Climate . 7 . 1286-1302. Pittock, A. 1980: Patterns of climate variations in Argentina and Chile Y. Precipitation, 1931-1960. Mon. Weath. Rev. . 108 . 1347-1360. Rao, V. B. and K. Hada, 1990: Characteristics of rainfall over Brazil: Annual variations and connections with the Southern Oscillation. Theor. Appl. Climatol . 42 . 81-90. Rao, V. B. I. F. Cavalcanti, and K. Hada, 1996: Annual variation of rainfall over Brazil and water vapour characteristics over South America. J. Geophys. Res., 101 . 26539-26551. Robertson, A. and C. Mechoso, 1998: Interannual and decadal cycles in river flows of Southeastern South America. J. Climate . 11 . 2570-2581. Robertson, A. W. and C. R. Mechoso, 2000: Interannual and interdecadal variability of the South Atlantic Convergence Zone. Mon. Wea. Rev . 128 . 2947-2957. Robertson, A. W. C. R. Mechoso, and N. O. Garcia, 2001: Interannual prediction of river flows in southeastern South America. Geophys. Res. Lett . in press. Ropelewski, C. H. and S. Halpert, 1987: Global and regional scale precipitation patterns associated with the El Nintildeo/Southern Oscillation. Mon. Wea. Rev. . 115, 1606-1626. Ropelewski, C. H. and S. Halpert, 1989: Precipitation patterns associated with the high index phase of the Southern Oscillation. J. Climate . 2 . 268-284. Rusticucci, M. and O. Pentildealba, 1997: Relationship between monthly precipitation and warm/cold periods in Southern South America. Preprints: Fifth Int. Conf. on Southern Hem. Met. and Ocean . 298-299. Sahin, M. J. and M. J. Hall, 1996: The effects of afforestation and deforestation on water yields. Jour. of Hydrology, 178 . 293-309. Saraiva, J. M. B. and P. L. Silva-Dias, 1997: A case study of intense cyclogenesis off the southern coast of Brazil: Impact of SST, stratiform and deep convection. Fifth AMS Conference on Southern Hem. Met. and Ocean . 368-369. Schuler, A. E. J. M. M. Moraes, L. C. Milde, J. D. Groppo, L. A. Martinelli, R. L. Victoria, M. L. Calijuri, 2000: Anaacutelise da representatividade fiacutesica dos paracircmetros do topmodel em uma bacia de meso escala localizada nas cabeceiras do rio Corumbataiacute, Satildeo Paulo. Revista Brasileira de Recursos Hiacutedricos Volume 5 - n. 2 Abr/Jun. Silveira, L. 1998: Hydrological Modelling of Natural Grasslands with Small Slopes in Temperate Zones. Doctoral thesis. Division of Hydraulic Engineering. Department of Civil and Environmental Engineering. Royal Institute of Technology, Stockholm, Sweden. ISRN KTH/AMI/PHD 1022-SE. Silveira, L. 2000: Large scale basins with small to negligible slopes. Part II: Hydrological Modelling. Nordic Hydrology - An International Journal. Vol. 31(1), 27-40. Schwerdtfeger, W. and C. J. Vasino, 1954: La variacioacuten secular de las precipitaciones en el este y centro de la Repuacuteblica Argentina. Meteor . IV. Ndeg3. pp 174-193. Swarts, F. A. (ed.) 2000: The Pantanal of Brazil, Bolivia and Paraguay Selected Discourses on the Worlds Largest Remaining Wetland System. 287, Waterland Research Institute Tanajura, C. A. S. 1996: Modeling and analysis of the South American Summer Climate. Ph. D. Thesis Dissertation, University of Maryland. Tucci, C. E. M 1991 International studies on climate change impacts Uruguay river basin. In: Workshop on Analysis of Potential Climate Changes in the Uruguay River Basin. Porto Alegre. IPH/UFRGS. Tucci, C. E. M. 1996 Estudos hidrologicos - hidrodinamicos do rio Iguaccedilu na Regiatildeo Metropolitana de Curitiba. Curitiba: Secretaria de Estado do Planejamento e Coordenaccedilatildeo Geral do Parana. 2v. 30cm. Tucci, C. E. M. 1998 Modelos hidroloacutegicos . ABRH Editora da UFRGS. Porto Alegre. 669 p. Tucci, C. E. M. and A. Damiani, 1994: Potencial impacto da modificao climaacutetica no Rio Uruguay. RBE, Caderno de Recursos Hiacutedricos . 12. 5-34. Tucci, C. E. M. and R. T. Clarke, 1998: Environmental issues in the La Plata Basin. Water Resources Development . 14 . 157-174. Tucci, C. E. M. Genz, F. Clarke, R. T. 1999: The Hydrology of Upper Paraguay Basin. In Biswas, A. Latin American Water Forum United Nations University Press. Valdeacutes, J. B. D. Entekhabi, H-M Shin and H-H Hsieh, 1999: An Evaluation of the Impact of ENSO on the Discharges of the Salt River, Arizona. Proceedings of the 26th Annual Conference of the ASCE Water Resources Planning and Management Division, Tempe AZ. VAMOS Document, 1997: clivar. ucar. edu/vamos. html. Vargas, W. M. J. Minetti, and A. Poblet, 1995: Statistical study of climatic jump in the regional zonal circulation over South America. J. Meteor. Soc. Japan . 73 . 1-8. Venegas, S. L. Mysak, and N. Straub, 1998: Atmosphere-ocean coupled variability in the South Atlantic, J. Climate . 10. 2904-2920. Vera, C. S. P. Vigliarolo, and E. H. Berbery, 2001: Cold season synoptic scale waves over subtropical South America. Mon. Wea. Rev. . submitted. Virji, H. 1981: A preliminary study of summertime tropospheric circulation patterns over South America estimated from cloud winds. Mon. Wea. Rev . 109 . 596-610. Wang, M. and J. Paegle, 1996: Impact of analysis uncertainty upon regional atmospheric moisture flux. J. Geophys. Res . 101 . D3, 7291-7303. Wood, E. F. 1991: Global scale hydrology - Advances in land surface modeling, Reviews of Geophysics 29: 193-201, Part 1, Suppl. S. Wood, E. F. D. P. Lettenmaier, X. Liang, B. Nijssen, and S. W. Wetzel. 1997. Hydrological modeling of continental-scale basins. Annu. Rev. Earth Planet. Sci . 25 . 279-300. World Conference on Preservation and Sustainable Development in the Pantanal: pantanal. org/Mainpant. htm Xie, P. and P. Arkin, 1997: Global precipitation: a 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bulletin of the American Meteorological Society . Boston, MA, 78 (11): 2539-2558.
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