Aerosol mitigation matters to future water availability in the global monsoon region

Water availability, as measured by precipitation minus evaporation (P-E), is projected to increase in the 21st century across global monsoon regions. However, while the impacts of increased greenhouse gas (GHG) concentrations are highlighted in existing studies, the contribution of reduced anthropogenic aerosol (AA) emissions is likely to be overlooked. Here, utilizing single-forcing projections under the SSP2-4.5 scenario, we elucidate the fingerprints of GHG and AA forcings on future P-E evolution. We reveal that the future wetting trend is primarily driven by an increase in P-E during the wet season. The escalation of GHG concentrations is projected to increase P-E over Asian-African monsoon domains while decreasing it over American monsoon domains. Conversely, aerosol reductions will drive a transition from current widespread drying to future wetting. While both the GHG increase and AA reduction can elevate atmospheric moistening through radiative warming, the disparate P-E responses come from dynamic processes that favor drying trends in American monsoon domains under GHG forcing. In contrast, strengthened monsoon circulations contribute to a wetting trend in Asian monsoon domains under AA reductions, attributable to greater interhemispheric thermal contrast. Our finding highlights the importance of considering aerosol mitigation in climate risk assessment for densely populated monsoon regions.