Analysis of Current and Future SPEI Droughts in the La Plata Basin Based on Results from the Regional Eta Climate Model

We identified and analysed droughts in the La Plata Basin (divided into seven sub-basins) for the current period (1961–2005) and estimated their expected evolution under future climate projections for the periods 2011–2040, 2041–2070, and 2071–2099. Future climate projections were analysed from results of the Eta Regional Climate Model (grid resolution of approximately 10 km) forced by the global climate model HadGEM2-ES over the La Plata basin, and considering a RCP4.5 emission scenario. Within each sub-basin, we particularly focused our drought analyses on croplands and grasslands, due to their economic relevance. The three-month Standardized Precipitation Evapotranspiration Index (SPEI3) was used for drought identification and characterization. Droughts were evaluated in terms of time (percentage of time from the total length of each climate scenario), space (percentage of total area), and severity (SPEI3 values) of cells characterized by cropland and grassland for each sub-basin and climate scenario. Drought-severity–area–frequency curves were developed to quantitatively relate the frequency distribution of drought occurrence to drought severity and area. For the period 2011–2040, droughts dominate the northern sub-basins, whereas alternating wet and short dry periods dominate the southern sub-basins. Wet climate spread from south to north within the La Plata Basin as more distant future scenarios were analysed, due to both a greater number of wet periods and fewer droughts. The area of each sub-basin affected by drought in all climate scenarios was highly varied temporally and spatially. The likelihood of the occurrence of droughts differed significantly between the studied cover types in the Lower Paraguay sub-basin, being higher for cropland than for grassland. Mainly in the Upper Paraguay and in the Upper Paraná basins the climate projections for all scenarios showed an increase of moderate and severe droughts over large regions dedicated to crops and grasses. On the other hand, for the near future, the Lower Uruguay and the River Plata basins showed a decrease of drought severity compared to the current period. Projections suggest an increase in competition among uses in these regions and the need for a potential relocation of certain crops from the northern regions towards cooler regions located in the centre and south. Further research should consider other climate projections and perform high spatial resolution studies in localized areas.