Observed Runoff Variability and Projected Change in the La Plata Basin

The actual and potential impact of climate change scenarios on the runoff regime in the La Plata Basin was investigated within the framework of the CLARIS international research project. In the investigated basin, which includes Rio Parana at Parana-Santa Fe (2 500 000 km ) and measures 3 100 000 km at the outlet, a large number of reservoirs, as Yacireta and Itaipu, are located. A statistical analysis using Mann-Kendall test, Student's t-test; Spearman ρ test was conducted on long series of observed runoff and precipitation in the La Plata basin and statistically representative trends were observed for some data sets. An assessment of actual and projected hydrological regime was performed using Thornthwaite-Mather model to assess actual evapotranspiration, calibrated using soil storage capacity. An analysis of the impact of SRES A1B projections of the up to date ECHAM5 Global Circulation Model was then performed. The model predicts an increase of mean annual precipitation of about 3% and a temperature increase of 1.0 C in 2040. Accordingly an increase of potential evapotranspiration (+13%) and of effective evapotranspiration (+7%) and a decrease of 15% of annual runoff volume was foreseen, thus leading to a reduction of available volume for hydropower production.