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VULNERABILITY OF WATER RESOURCES AND TROPHIC STATE OF THE SANTA LUCIA RIVER LOWER BASIN AND ESTUARY TO CLIMATE VARIABILITY AND CHANGE Caffera MR, M Bidegain, F Blixen, CH Lpez, JJ Lagomarsino, GJ Nagy and K Sans Speakers Facultad de Ciencias, UdelaR, Montevideo, Uruguay

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THIS CONTRIBUTION DESCRIBES RECENT FINDINGS ON THE VULNERABILITY OF WATER RESOURCES OF THE SANTA LUCIA RIVER BASIN AND ESTUARY (SOUTHERN URUGUAY) TO CLIMATE VARIABILITY AND CHANGE. THIS BASIN SUSTAIN INTENSIVE AGRICULTURE, HOSTS 20,000 Has OF WETLANDS RICH IN BIODIVERSITY AND SUPPLIES DRINKING WATER FOR 60% OF THE NATIONS POPULATION. RIVER MOUTH IS AN ESTUARINE SYSTEM. IT IS LOCATED WITHIN THE BOUNDARIES OF THE ESTUARINE FRONT OF THE RIO DE LA PLATA WHICH SUPPLIES FRESH OR SALTWATER DEPENDING ON ITS LOCATION. BECAUSE OF LACK OF KNOWLEDGE ABOUT SOME RELEVANT PROCESSES WE HAVE FOCUSED ON BUILDING SCIENTIFIC CAPACITY TO UNDERSTAND BASIC PROCESSES AND FACTS, EMPHASIZING ON ENSO-RELATED VARIABILLITY

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Monthly average precipitations at Florida, Santa Lucia river middle basin 1990 - 2003 60,0 70,0 80,0 90,0 100,0 110,0 120,0 130,0 140,0 123456789101112 months mm

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Average temperature and precipitations in Central-southern Uruguay, Montevideo and Florida (1997 2003), and variation with regard to normal climatology (1961 1990). Source, DMM. Summer J-F-M Fall A-M-J Winter J-A-S Spring O-N-D Annual Temperature C 23.218.312.317.417.8 ( C)+0.4+0.8+0.9 +0.7 Precipitations (mm) 3573622432951256 (%)+29+2700+14 Temp. Mv22.218.112.116.417.2 ( C)0+0.8+0.9+0.4+0.5 Precipit. Mv3333602782931263 %)+22+45+6+1+15 Precipit. Fl. (mm) 3863292803731366 Prec. 1990- 2003 1276

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AIACC LA-32 Floods in Santa Luca river at middle and lower watershed, and embouchure

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AIACC LA32 R11 bridge Middle basin Las Brujas Lower basin Santiago Vzquez Estuarine zone

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R11 Bridge Station (Middle S ta Luca Basin)

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Santiago Vzquez Station (S ta Luca Estuarine zone)

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R11 bridge Middle basin

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Las Brujas Lower basin

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Estimation of precipitation on March 29, 2002

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A word on extreme events Water vapor low level flux From LA-26: sensitivity study for major floods in Uruguay river: flood wave ~ 12 days In Sta. Luca: ~ 6 days maximum Example: pattern for 15 winter major floods

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Concluding Remarks There is a significative ENSO Signal in the southernmost watershed of La Plata basin. It seems to be an increasing amplitude in levels. This could lead to an increase of ecological stress in freshwater ecology. There is a (recent) positive trend in the frequency of high levels increasing riverside vulnerability. Streamflow controls trophic state. In spite of the economic, environmental and social importance of Sta Luca WB, there is a considerable lack of data and knowledge.