Evapotranspiration dynamics and climatic-land-use controls in the Hanjiang River Basin, 2000-2018

Study region Hanjiang River Basin, China. Study focus This study investigates spatiotemporal dynamics of total evapotranspiration (ET) and its four components: dry canopy transpiration (ET_Canopy), wet canopy evaporation (E_Canopy), saturated soil evaporation (E_Soil), and moist soil evaporation (ET_Soil) from 2000 to 2018, using the physically-based ESSI-3 model with vertical transpiration partitioning. A multi-method framework (Random Forest, SHapley Additive exPlanations, Structural Equation Modeling) was employed to identify dominant drivers and causal pathways for total ET and ET_Canopy. New hydrological insights for the region Results reveal strong spatial heterogeneity and seasonal shifts in ET dominance over the study period: ET_Canopy prevails during the growing season, while E_Soil dominates in winter.Vegetation-related components (ET_Canopy, E_Canopy) exhibited increasing trends, while soil-related components (ET_Soil, E_Soil) declined, resulting in a net slight increase in total ET. Temperature, solar radiation, and leaf area index (LAI) are the primary drivers of these dynamics, exhibiting nonlinear and interactive effects on ET. In contrast, precipitation and soil water showed limited direct influence on the daily scale but contributed through lagged effects. Crucially, the transpiration attributable to plant root uptake from the second soil layer (5–30 cm) constituted the largest fraction (72.1 %) of total canopy transpiration, underscoring the role of mid-depth root zones in sustaining ET. This study provides a replicable framework for diagnosing ecohydrological processes and informs adaptive water management in monsoon-sensitive basins.