Projection of droughts and their socioeconomic exposures based on terrestrial water storage anomaly over China

Global warming has altered the thermodynamic and dynamic environments of the climate system, thus affecting the energy budget and water cycle process of the land-atmosphere system. Under changes in key hydrological elements such as precipitation, runoff, and terrestrial water storage, future drought variation remains a complex question. Existing studies have utilized terrestrial water storage anomaly (TWSA) in drought monitoring and assessment, but they usually focused on either drought duration or intensity, overlooking the multi-faced attributes of droughts as well as their socioeconomic impacts under a non-stationary condition. In this study, we first identify dry/wet conditions over China using GRACE/GRACE-FO satellite observations, and then evaluate the feedback effects of humidity and energy factors (e.g., sensible heat flux, latent heat flux, atmospheric relative humidity, and convective available potential energy) to drought events. Future changes in TWSA and dry/wet conditions are projected by eight Coupled Model Inter-comparison Project Phase 6 (CMIP6) global climate models (GCMs) under three shared socioeconomic pathways (SSPs), with their biases corrected by a trend-preserving quantile mapping method. The time-varying Copula function of drought duration and intensity is constructed by a moving windows method, and future bivariate drought risks are quantified with the most likely realization method. The population and GDP affected by increasing drought risks are finally quantified based on the SSPs data. It is found that the land-atmosphere coupling effects closely interact with drought evolution, and the uneven distribution of water resources is projected to be further aggravated, with most areas of China will be threatened by continuous drying tendency. By the end of the century, the duration of moderate, severe and exceptional droughts in some regions of China will double, and the drought intensity will increase by over 80%. For the 50-year bivariate droughts during the historical period, their occurrence may increase by 5-10 times in several regions, and might affect about 35-55% of China's population and GDP at the end of 21st century.