Watershed Characteristics Modulate the Global Response of Fractional Evapotranspiration to Wet Climate Extremes

Abstract

Intensifying wet extremes under continued warming threaten water security and ecosystem functioning by perturbing land–atmosphere water fluxes. Yet, the watershed‐scale controls on how wet‐event intensity and duration translate into changes in fractional evapotranspiration (fET) remain poorly constrained at global scales. Here, using monthly wet climate extreme indices (CEIs) and fET across ∼986 global watersheds, we quantify CEI–fET coupling and attribute its spatial variability to watershed properties using Random Forest models and SHapley Additive exPlanations (SHAP). Across event types, soil organic carbon (SOC) and groundwater table depth (GWT) consistently structure coupling regimes, indicating a robust role for soil state and subsurface storage. However, the dominant texture axis differs by extreme type: intensity‐based extremes are most strongly organized by SOC–GWT–clay regimes, consistent with pulse retention and buffering, whereas duration‐based extremes are organized by SOC–GWT–silt regimes and permafrost‐related constraints, consistent with persistence‐driven drainage and saturation sensitivity. Supported SHAP‐transition analysis identifies data‐constrained regime boundaries. Lagged correlations further reveal multi‐timescale behavior: coupling varies at short lags but tends to shift toward negative associations at longer lags, especially for duration‐based extremes. In a permafrost‐limited subset, vegetation state and topography become more prominent predictors, highlighting how cold‐region constraints alter which attributes dominate. Together, these results provide a globally consistent diagnostic framework for identifying watershed regimes where intensifying wet extremes are more likely to yield sustained evapotranspiration responses versus reduced fET sensitivity. By quantifying regime thresholds, the study offers a diagnostic framework that may inform targeted mitigation strategies and policy frameworks, such as IPCC adaptation guidelines.