Is Southeastern South America Turning Wetter?

Changes in hydroclimatological conditions for South America have been examined using an ensemble of regional climate models. Annual mean precipitation (P), evapotranspiration (E) and potential evapotranspiration (E_P) are jointly considered through the balances of land water and energy. Drying or wetting conditions, associated with changes in land water availability and atmospheric demand, are analysed in the Budyko space. The water supply limit (E limited by P) is exceeded at about 4% of the grid points, while the energy limit to evapotranspiration (E = E_P) is overall valid. Most of the continent, except for the southeast and some coastal areas, presents a shift toward drier conditions related to a decrease in water availability (the evaporation rate E / P increases) and, mostly over much of Brazil, to an increase in the aridity index (Ф = E_P / P). These changes suggest less humid conditions with decreasing surface runoff over Amazonia and the Brazilian Highlands. In contrast, Argentina and the coasts of Ecuador and Peru are characterized by a tendency toward wetter conditions associated with an increase of water availability and a decrease of aridity index, primarily due to P increasing faster than both E and E_P. This trend towards wetter soil conditions suggest that the chances of having larger periods of flooding and enhanced river discharges would increase over parts of south eastern South America. Interannual variability increases with Ф and with climate change. In particular, interannual variability increases over the Brazilian Highlands and decreases in central-eastern Argentina.