Response of Soil Moisture Deficits to Compound Droughts and Hot Extremes Across the Yangtze and Yellow River Basins

Compound droughts and hot extremes (CDHEs) can exert higher impacts on water resources, agricultural production and ecosystems, among others. Though the low precipitation and high temperature leading to reduced soil moisture have been well documented, the quantitative estimation of the impact of CDHEs on soil moisture deficits (or agricultural droughts) has been rather limited. In this study, we investigated the distinct response of soil moisture deficits to CDHEs across two major basins in China, the Yangtze River Basin (YZRB) (mostly humid regions) and the Yellow River Basin (YRB) (mostly arid and semi-arid regions). We found the response of soil moisture deficits is stronger under CDHEs compared with individual meteorological droughts (precipitation deficits). In addition, due to the difference in evapotranspiration response, the physical processes of soil moisture deficits responding to CDHEs in the YZRB differ from those in the YRB. The differences in meteorological factors (e.g., rainfall, temperature, vapour pressure deficit, radiation and evapotranspiration) leading to soil moisture deficits under individual meteorological droughts and CDHEs are also investigated. The case study of the record CDHEs during 2022 further demonstrates the response pattern of soil moisture deficits and associated driving factors. These results highlight the importance of considering different climate regions in understanding the impact of CDHEs on agricultural droughts.