Dominating controls for wetter South Asian summer monsoon in the twenty-first century

Abstract

This paper analyzes a suite of global climatemodels fromphase 5 of the CoupledModel IntercomparisonProject (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to enhanced radiative forcing during the twenty-first century. An increase in radiative forcing fuels an increase in the atmospheric moisture content throughwarmer temperatures, which overwhelmsthe weakening of monsoon circulation and results in an increase of moisture convergence and therefore summer monsoon precipitation over South Asia. Moisture source analysis suggests that both regional (local recycling, the Arabian Sea, theBay of Bengal) and remote (including the south Indian Ocean) sources contribute to themoisture supply for precipitation over SouthAsia during the summer season that is facilitated by themonsoon dynamics. For regional moisture sources, the effect of excessive atmosphericmoisture is offset byweakermonsoon circulation and uncertainty in the response of the evapotranspiration over land, so anomalies in their contribution to the total moisture supply are eithermixed or muted. In contrast, weakening of themonsoon dynamics has less influence on themoisturesupply fromremotesources thatnotonlyis adominantmoisture contributor inthehistorical periodbut is also the net driver of the positive summermonsoon precipitation response in the twenty-first century. The results also indicate that historic measures of the monsoon dynamics may not be well suited to predict the nonstationary moisture-driven South Asian summer monsoon precipitation response in the twenty-first century.