Multimodel assessment of sensitivity and uncertainty of evapotranspiration and a proxy for available water resources under climate change

Partitioning of precipitation (P) into actual evapotranspiration (ET) and runoff affects a proxy for water availability (P-ET) on land surface. ET accounts for more than 60% of global precipitation and affects both water and energy cycles. We study the changes in precipitation, air temperature, ET, and P-ET in seven large basins under the RCP 2.6 and 8.5 scenarios for the projected future climate. While a majority of studied basins is projected to experience a warmer and wetter climate, uncertainty in precipitation projections remains large in comparison to the temperature projections. Due to high uncertainty in ET, uncertainties in fraction of precipitation that is evaporated (ET/P) and a proxy for available water (P-ET) are also large under the projected future climate. Our assessment showed that under the RCP 8.5 scenario, global climate models are major contributors to uncertainties in ET (P-ET) simulations in the four (six) basins, while uncertainty due to hydrological models is prevailing or comparable in the other three (one) basins. The simulated ET is projected to increase under the warmer and wetter future climates in all the basins and periods under both RCPs. Regarding PET, it is projected to increase in five out of seven basins in the End term (2071-2099) under the RCP 8.5 scenario. Precipitation elasticity and temperature sensitivity estimated for ET were found to be positive in all the basins under the RCP 8.5 scenario. In contrast, the temperature sensitivity estimated for (P-ET) was found to be negative for all the basins under the RCP 8.5 scenario, indicating the role of increased energy availability and limited soil moisture. Our results highlight the need for improvements in climate and hydrological models with better representation of soil, vegetation, and cold season processes to reduce uncertainties in the projected ET and P-ET.