Propagation of soil moisture droughts in a hotspot region: Spatial pattern and temporal trajectory

Droughts evolve in space and time simultaneously, but its spatio-temporal propagation remains less explored. As one of the hotspot regions in global soil moisture (SM) drought, the Southeastern Asia supports billions of population and trillions of dollars in gross domestic product. Its high drought risk initiated a deep understanding of drought propagation in multiple dimensions for effective prevention. This study investigated the SM droughts with a merged dataset of remote sensing and land surface modeling over 1979–2016. Our results showed that 369 drought clusters and 145 drought events occurred. Spatially, severe droughts appeared mainly in southwest and northeast of the study region. Temporally, the droughts were more severe in cold season (winter and spring) than warm season (summer and autumn). In last four decades, the SM droughts alleviated in warm season but aggravated in cold season significantly, posing a challenge for drought mitigation, especially for spring crop growth vigorously. Furthermore, the drought clusters shared two predominant routes of westward and southwest. The westward route is for the droughts started in winter in south region, while the southwest route is for the droughts started in summer across the Yangtze River basin from northeast to southwest. At a drought event level, the SM drought propagated synergistically with precipitation and potential evapotranspiration (PET). Precipitation was generally the primary driver and PET the secondary, particularly for SM droughts lasting in summer and winter in south region. The intensity of PET usually enhanced in spring and summer with temperature increasing and crop growing. The findings in drought propagation provide essential spatiotemporal structure for mechanism exploration and important clues for drought prediction.