Climate-change impact on reservoir evaporation and water availability in a tropical sub-humid region, north-eastern Brazil

Abstract. The potential effects of climatic changes on water resources are crucial to be assessed, particularly in dry regions such as Northeast Brazil (1 million km²), where water supply is highly reliant on open-water reservoirs. This study analyses the impact of evaporation (by the Penman method) on water availability for four scenarios based on two regional climatic models (Eta-CanESM2 and Eta-MIROC5) under the Representative Concentration Pathways 4.5 and 8.5. We compared the water availability in the period of 2071–2100 with that of the historical period (1961–2005). The scenarios derived from the Eta-CanESM2 model indicate an increase in dry season evaporative rate (2 % and 6 %, respectively) by the end of the century. Unlike the above scenarios, the ones derived from the Eta-MIROC5 model both show a decrease in dry season evaporative rate of −2 %. Consequently, for a 90 % reliability level, the expected reservoir capacity to supply water with high reliability is reduced in 80 %. It is reasonable to state that both patterns of future evaporation in the reservoirs may prove to be plausible. Because model-based projections of climate impact on water resources can be quite divergent, it is necessary to develop adaptations that do not need quantitative projections of changes in hydrological variables, but rather ranges of projected values. Our analysis shows how open water reservoirs might be impacted by climate change in dry regions. These findings complement a body of knowledge on estimation of water availability in a changing climate and provide new data and insights on water management in reservoir-dependent drylands.