Abstract:Climate change over drylands in a warmer climate and its responses to Earth's orbit can be better understood by an investigation of climate change across arid Central Asia during the Last Interglacial (LIG).Based on the Paleoclimate Modelling Intercomparison Project Phase 4 (PIMP4), we analyze variations in wet-dry conditions and associated mechanisms over arid Central Asia during the LIG.The results show that during the LIG, the annual precipitation is reduced by 0.7% over arid Central Asia, with precipitation decreasing by 2.8% over Central Asia while increasing by 1.8% over Xinjiang compared to the preindustrial period.Over Central Asia, the precipitation decreases by 1.8%, 1.3%, 1.5%, and 10.3% in the spring, summer, autumn, and winter, respectively, indicating that the reduced annual precipitation is mainly due to changes in winter.According to the moisture budget equation, variations in precipitation over Central Asia during the rainy season (winter and spring) are mainly caused by the vertical dynamic term.Moreover, precipitation over Xinjiang is reduced by 5.9% and 3.8% in spring and winter, respectively, and increased by 14.1% in summer and 8.6% in autumn, indicating that the majority of the rise in annual precipitation is a result of precipitation in summer.Consequently, the moisture budget analysis suggests that the vertical dynamic and thermodynamic terms contribute most to the variations in precipitation over Xinjiang.In addition, the aridity index over arid Central Asia decreases by approximately 10.2% during the LIG based on the Penman-Montieth method, which indicates that arid Central Asia experience a drier condition.Furthermore, drylands over arid Central Asia had expanded during that period, including the transition from semi-arid to arid regions, from sub-humid and semi-arid to arid regions, and from humid to sub-humid, semi-arid and arid regions.Hence, the reduced aridity index over arid Central Asia is a result of increased potential evaporation at that time.This increased evaporation is further linked with negative contributions from decreased surface air temperature and increased relative humidity, as well as positive contributions from enhanced surface wind speed and available energy.Our study provides a possible map for changes in wet-dry conditions over arid Central Asia in a warmer climate induced by the Earth's orbit and sheds light on risk assessments for arid Central Asia in different warming scenarios.