Impact of Rising Compound Drought and Heatwaves on Vegetation in Global Drylands

Compound Drought and Heatwave events (CDHWs) are increasing in frequency across dryland ecosystems, yet their impacts on vegetation remain insufficiently studied. In this study, we develop a new CDHWs index that integrates a four-day Standardized Soil Moisture Index (SSMI) with heatwaves index. Employing an interpretable machine learning model, we quantitatively analyzed the effects of various environmental factors on vegetation during CDHWs. Results demonstrate significant upward trends in CDHW frequency, intensity, and maximum duration across global drylands. Analysis indicates that 65% of CDHWs negatively affect vegetation, 20% produce positive effects, and 15% result in minimal impact. Accumulated Local Effects (ALE) and Partial Dependence Plot (PDP) analyses identify maximum temperature as the primary factor driving negative vegetation responses, while soil moisture emerges as the predominant factor associated with positive responses. Projections under multiple Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios (SSP245 and SSP585) indicate continued increases in CDHW frequency, intensity, and maximum duration through 2054. These findings underscore the necessity for fine-scale monitoring of compound extremes and offer actionable insights for adaptive management in dryland regions.