Stratospheric Aerosol Injection Geoengineering Would Mitigate Greenhouse Gas-Induced Drying and Affect Global Drought Patterns

Stratospheric aerosol injection (SAI) is suggested as a potential measure for alleviating global warming. The potential effects of SAI on global temperature and precipitation have been extensively discussed, but its impact on drought has received little attention. Based on the simulations from the G6sulfur experiment that employs SAI to reduce the global mean surface temperature from the level of high-tier forcing (Shared Socioeconomic Pathways SSP5-8.5) scenario to that of medium-tier forcing (SSP2-4.5) scenario, we investigate the drought response to SAI via the standardized precipitation evapotranspiration index. During 2081-2100, SAI effectively offsets the greenhouse gas-induced aridity trend by increasing the climate water balance at the global scale. Drought duration and severity decrease but drought frequency increases under SAI forcing. Robust wetting responses occur over most regions, especially the Sahara, South America, southern Africa and Australia, while Alaska, Greenland, Southeast Asia, and tropical Africa face enhanced drought due to SAI. Relative to the SSP2-4.5 scenario, the regional drying and wetting patterns in G6sulfur are remarkably different. Notably, in tropical Africa, SAI reverses the wetting caused by greenhouse gases and induces severer drought. The drought pattern changes are largely due to evaporative demand alterations caused by the vapor pressure deficit response. Stratospheric aerosol injection (SAI), by injecting sulfate aerosols into the stratosphere to scatter part of sunlight back to space, is a proposed geoengineering method to counteract anthropogenic global warming. Previous studies have confirmed that SAI can partially offset the climate change caused by increased greenhouse gas (GHG) concentrations. However, one of the concerns is that SAI may increase drought risk in some regions. Here, we have investigated drought response to SAI using simulations from state-of-the-art climate models. Stratospheric aerosol injection would effectively mitigate the drought in high GHG forcing scenario globally. The duration and severity of drought events would decrease over most landmasses. Meanwhile, the responses of climate water balance to SAI and GHG are different, causing a dramatic change in drought patterns. Some regions especially tropical Africa would face severe drying. Such drought-related regional inequality caused by SAI reminds us to be cautious when considering geoengineering to counteract climate change. Stratospheric aerosol injection (SAI) would mitigate drought in a high CO2 emissions scenario with reduced drought duration and severity SAI would modify the drought pattern relative to the targeted forcing scenario, causing particularly severe drought in tropical Africa Vapor pressure deficit response plays an important role in the drought pattern change under SAI forcing