Soil moisture deficits triggered by increasing compound drought and heat events during the growing season in Arid Central Asia

Global warming is progressively intensifying, leading to more frequent Compound Drought and Heat Events (CDHEs). Arid Central Asia is highly sensitive to climate change, highlighting the necessity to comprehensively understand the occurrence and development patterns of CDHEs in this region. This study employs the Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Temperature Index (STI), and Standardized Soil Moisture Index (SSMI) alongside the Vine Copula method to investigate the spatial and temporal variations of CDHEs and their impact on soil moisture deficits. The results indicate that: (1) Over the past six decades, high temperatures and drought conditions have continuously deteriorated, with a significant escalation since the 1990 s, resulting in persistent soil moisture deficits, particularly during summer. (2) All levels of CDHEs have shown an increasing trend over time, with mild CDHEs occurring most frequently, whereas extreme CDHEs exhibit the most extended durations and highest severities. In the most recent two decades (2001–2020), CDHEs have been the most frequent, severe, and prolonged, primarily concentrated in the eastern and western regions of Arid Central Asia. (3) Under CDHEs, high-probability soil moisture deficit areas are primarily concentrated in the central region, demonstrating a spatial aggregation effect that extends from southwest to northeast. (4) Different vegetation cover types exhibit varying degrees of soil moisture deficit responses to CDHEs. Grasslands are the most sensitive, croplands are intermediate, and forests are the least responsive. However, all three vegetation types show an increasing probability of soil moisture deficits during the growing season over time. (5) The probability of CDHE occurrence gradually increases with higher emission pathways (SSP126, SSP245, and SSP585). The central region experienced the greatest increases. And the largest increase in extreme CDHEs is more than 100 %. Under various levels of CDHEs, the central and western regions show the most considerable soil moisture deficits, with increases surpassing 80 %. Consequently, these areas will face more significant risks of soil moisture deficits in the future.