Anthropogenic aerosol reduction contributes to faster flash drought onset in a changing climate

Flash droughts have emerged as severe hazards, posing growing challenges to natural and socioeconomic systems, yet the influence of recent aerosol reductions on their onset remains unclear. Here, we investigate the impacts of aerosols and their underlying mechanisms using multi-source observations and large-ensemble climate simulations. Lower aerosol levels are increasingly linked to severe soil moisture deficits, with aerosol effects on onset-speed variability intensifying across 69.2% of regions. During the onset stage, air temperature pathways associated with aerosol variability account for a larger fraction of onset-speed variability than pathways linked to atmospheric demand. Aerosols have long acted to dampen flash drought development; however, their reduction, acting within a warming climate, contributes to faster flash drought onset. As aerosol emissions decline in the future, the area at higher risk of flash drought acceleration in aerosol-forced simulations is projected to increase by 11.7% during 2070–2099 relative to the historical period of 1990–2019. Anthropogenic aerosol reduction contributes to faster flash drought onset by enhancing soil moisture depletion induced by higher temperature and increased shortwave radiation.