Characterization of the Regional Hydrological Cycle of the La Plata Basin

The goal of this work is to investigate the influence of meteorological systems in the hydrological cycle of the La Plata Basin (LPB) in South America, and how they affect the precipitation regime over that region. The most important atmospheric systems in LPB are the South America Monsoon and the Mesoscale Convective Systems (MCS) during the warm season (October-April), and mid-latitude synoptic scale systems during the cold season (May-September). We computed the monthly water budget from 1979 to 2002, using the Modern Era Retrospective-Analysis for Research and Applications (MERRA), from NASA Global Modeling and Assimilation Office (GMAO). During the period studied we observed a water gain through the northern edge of the control volume enclosing the LPB region during the austral summer whereas a water deficit was observed during the winter. Results also show that precipitation in general exceeds evaporation, suggesting that moisture is being contributed from other regions. Results also indicated that runoff is in general in phase with changes in the total water storage. One of the major sources of humidity to the LPB is the Amazon region from where moisture is transported by a Low Level Jet (LLJ) east of the Andes. Results from a case study show that despite the losses along the way the humidity carried into the basin by the LLJ has a substantial impact in the MCS occurrences and rainfall associated to those systems.