Future changes in atmospheric rivers over East Asia under stratospheric aerosol intervention

Abstract. Atmospheric rivers (ARs) are closely associated with historical extreme precipitation events over East Asia. The projected increase in such weather systems under global warming has been extensively discussed in previous studies, while the role of stratospheric aerosol, particularly for the implementation of stratospheric aerosol intervention (SAI), in such a change remains unknown. Based on an ensemble of the UK Earth System Model (UKESM1) simulations, here we investigate changes in the frequency of ARs and their associated mean and extreme precipitation under a range of climate forcing, including greenhouse gas emission scenarios of high (SSP5-8.5) and medium (SSP2-4.5) levels, the deployment of SAI geoengineering (G6sulfur) and solar dimming (G6solar). The result indicates a significant increase in AR frequency and AR-related precipitation over most of East Asia in a warmer climate and the most pronounced changes are observed in southern China. Comparing to G6solar and both the SSPs scenarios, the G6sulfur simulations indicate that SAI is effective in partly ameliorating the increases in AR activity over the subtropical region; however, it may result in more pronounced increases in ARs and associated precipitation over the mid-high latitude regions, particularly northeastern China and Japan. Such a response is associated with the further weakening of the mid-latitude westerly jet stream under SAI that favours the high-latitude AR activity. This is driven by the decreased meridional gradient of thermal expansion in the mid-high troposphere associated with aerosol cooling across the tropical region, though SAI effectively ameliorates the widespread increase in thermal expansion under climate warming. Such a side effect of SAI over the populated region implies that caution must be taken when considering geoengineering approaches to mitigating hydrological risk under climate change.