East Asian Anthropogenic Aerosols Strongly Influence Past and Present Southern African Hydroclimate and Ecosystem Changes

Abstract. Southern Africa (SA) is highly sensitive to rainfall changes, as water availability significantly influences agriculture, ecosystems, and the region's socio-economic stability. Observations reveal substantial multi-decadal changes in December–February precipitation during the second half of the 20^th century, characterized by enhanced rainfall over the southern part of SA (hereafter SSA), including Madagascar (MDG), and drying to the north. More recently, however, this long-term wetting tendency has reversed, with widespread drying observed across much of the region since the mid-2000s. Despite their global significance, their impact of anthropogenic aerosols on southern African precipitation has received limited attention, and the underlying mechanisms remain unclear. We show that East Asian (EAS) anthropogenic aerosols played a key role in driving enhanced precipitation over SSA and MDG between 1945 and 2005, alongside the influence of internal variability. Increased EAS sulfate emissions strengthened interhemispheric temperature and pressure gradients, inducing a southward shift of the Intertropical Convergence Zone and associated Hadley circulation, thereby enhancing moisture convergence over SSA and MDG. After the mid-2000s, rapid reductions in EAS aerosols reversed this circulation response and contributed to declining precipitation. Applying this physical framework to near-future scenarios from the Regional Aerosol Model Intercomparison Project further suggests that continued reductions in aerosols will lead to further hydroclimatic adjustments. The recent decline in precipitation (2006–2020) coincides with reduced gross primary productivity and leaf area index, as well as intensified fire-weather conditions. These findings highlight the sensitivity of southern African hydroclimate and ecosystems to remote anthropogenic aerosol emissions.