Anthropogenic Impacts on Asian Drought Trends: Distinct Effects of Greenhouse Gases and Aerosols

This study investigates the impacts of anthropogenic aerosols and greenhouse gases (GHGs) on drought trends in Asia using CMIP6 models simulations under different forcings. The analysis focuses on the meteorological drought measured by the 24-month standardized precipitation index (SPI24). The results show that anthropogenic aerosols and GHGs have distinct effects on Asian drought trends. Aerosols dominate the drying trend in East Asia, whereas GHGs drive the wetting trend in Central Asia. In South Asia, their impacts tend to offset each other with aerosols playing a larger role. Moisture budget analysis indicates that the changes in the vertical motion are the primary drivers of drought changes in Asia. Aerosols-induced stronger cooling of midlatitude continents reduces the land-sea thermal contrast, which in turn weakens the summer monsoon circulation and suppresses precipitation over South and East Asia. Conversely, GHG-induced strengthening of the westerly jet stream contributes to the alleviation of drought in Central Asia. Both the cooling effect of aerosols and warming effect of GHGs are stronger in the Norther Hemisphere, leading to an asymmetric change between the two hemispheres and causing a meridional shift of intertropical convergence zone (ITCZ), which influences drought changes in South Asia.