Abstract:It is vital to evaluate and predict regional water resource variation and its influencing factors for sustainable development of arid and semi-arid areas. Based on four global climate models of CMIP5 and CLM 4.5, the temporal and spatial characteristics of evapotranspiration and water availability were studied in Inner Mongolia under two Representative Concentration Pathways (RCPs) from 2020 to 2099. The results showed that under RCP 6.0 and RCP 8.5 scenarios, the future evapotranspiration in Inner Mongolia would increase at a rate of 0.37 mm/a and 0.69 mm/a, respectively (p<0.05), decreasing form east to west. Water availability in Inner Mongolia did not show a significantly trend under the two scenarios (p>0.05), but there were significant spatial differences.From a spatial perspective, water availability in most areas showed an increasing trend and increased by more than 10 mm/a in the southern semi-arid and semi-humid regions of temperate zone by 2090s; however, the area with reduced water availability accounted for 46.32% of the entire territory under the RCP 8.5 scenario, especially in the arid, semi-arid and semi-humid areas. There were great regional differences influencing of driving factors in evapotranspiration. Precipitation was the main influencingfactor of evapotranspiration changes in arid and semi-arid area. The changes in semi humid area were jointly affected by precipitation and temperature. The changes in humid area were dominated by temperature and in the higher heating scenario, the effect further increased with temperature increased. At the same time, vegetation was also an important factor affecting evapotranspiration with less than climate factor.