Extreme rainfall, hydric conditions and associated atmospheric circulation in the southern la Plata Basin

Abstract

The interaction between land surface and atmosphere plays an important role in the climate system. Soil-atmosphere feedback mechanisms are analyzed by calculating the hydric condition (HC) of the soil from the water balance. Spatial coherence between HC and the Standardized Precipitation Index (SPI) as well as the circulation patterns associated with rainfall shortages and excess was evaluated over the southern La Plata Basin, fulfilling one of the objectives of the CLARIS LPB project. Monthly precipitation, and maximum and minimum temperatures registered at 35 stations over the 1961-2008 period were used to calculate the HC and SPI indices while the characteristics of the associated circulation were derived from daily sea level pressure fields from NCEP DOE Reanalysis 2 for a domain covering South America. Our results show that the HC responds better to accumulated precipitation anomalies in relatively short time scales. Dry and wet months were selected based on the SPI, according to several thresholds that define the spatial extension of these events. This analysis depends on the region, indicating the diversity of dry and wet events. Nevertheless, spatial coherence between both indices was found for regional extreme events. The analysis of the circulation showed that specific daily surface circulation types contribute to wet and dry cases and have a predominant occurrence related to the climatology in the development of the extreme hydric events in the region. This research complements previous studies carried out with modeled data and shows the complexity in the propagation of the precipitation anomalies through the soil/land surface.