An Observed Trend of Precipitation in the PROSUR Area of South America Brant Liebmann Carolina S. Vera Leila M.V. Carvalho Ines Camilloni Marty P. Hoerling Dave Allured Tendencia de precipitacão observada na area PROSUR da America do Sul

Se um evento de inundacão esta definido como dois desvios- padrão da anomalia mensal do fluxo em Corrientes, Argentina, então existem quase seis vezes mais inundacões nos 20 anos entre que existiram nos 60 anos entre

Previous work: Barros, Castaneda, Doyle (2000): Increase in precipitation over most of Argentina from Decrease in meridional temperature gradient. Castaneda and Barros (1994): Humid Pampa increase in rain, mainly after Vargas (1987): Grimm: Marengo:

Data We wish to thank the following agencies for providing the data used in this study: Agência Nacional de Águas (Brasil) Agência Nacional Energia Elétrica (Brasil) U.T.E. Uruguay C.T.M. Salto Grande Servicio Meteorologico Nacional (Argentina, Paraguay, Uruguay) FUNCEME (Ceará, Brasil) SIMEPAR (Paraná, Brasil) DAEE (São Paulo, Brasil) Minesterio del Ambiente y los Recursos Naturales (Venezuela) Meteorogische Dienst Suriname METEO-France

Climatology January-March TotalDecember-February Total

Index:47W-53W 23S-29S “southern Brasil”

JFM climo JFM climo

JFM climo difference – 1994/99 minus 1976/81

What are the characteristics of the observed trend? Quais são as caracteristicas da tendencia observada?

Slope = 3.87 mm/yr Slope = 3.16 mm/yr Slope = mm/yr Slope = -1.2 mm/yr

A(dia) = Acumulación anómala R(n) = lluvia diaria R = promedio anual de precipitación diaria Se considera que la estación lluviosa tiene lugar cuando la pendiente de la curva es positiva ( R(n) > R ).

Fecha promedio de iniciación: 30 de diciembre Este Central de la Amazonia

Average onset date = 25 October 1 January

Average onset date = 25 OctoberAverage end date = 9 April 31 March

Average onset date = 25 OctoberAverage end date = 9 April

difference Rainy day average = Percent dry days =

Is observed precipitation trend due to a change in synoptic variability? Esta tendencia é devido a mudanca na variabilidade sinotica?

statistical significance of trend 95% 97.5% 99% Trend in JFM daily 700 mb heat flux ( ) _ +

Is there a relationship between observed precipitation trend and sea surface temperature? Esta tendencia observada na precipitacão esta relacionada a temperatura da superficie do mar (TSM)?

Simultaneous Correlation

Available stations Available stations

Slope: = = = 1.53

Slope (m3/s/yr): = = = 17.2 Precipitation has increased by 35% (along trend line) River flow has increased by 161% (amplification and delay noted by Berbery and Barros (2002))

Slope: = deg/yr = = Slope: = 7.20 mm/yr = = 1.53 SST in southwest AtlanticJan-March rainfall Season rainfall (mm/yr) Jan-Mar SST (C)

95% ‘significant’ Using 2-sided t-test

An observed positive precipitation trend during the rainy season in Southern Brazil is most prominent from , but is evident earlier. The trend is consistent with a change in river flow. The trend is characterized by an increase in the number of rainy days per season and an increase in the amount per rainy day. The precipitation trend is related to one in SST, although perhaps not causally. The SST trend seems to result from a decrease in the strength of the South Atlantic high.