Résumé
Evapotranspiration (ET) lies at the core of the energy-water-carbon coupling, particularly under changing climate conditions. Yet, the sensitivity of ET models to key environmental drivers remains insufficiently understood, especially in understanding how thermal-based ET models respond to distinct influences of soil and atmospheric water stress across ecosystems. In this study, we examine the sensitivity of ET to key environmental drivers, including land surface temperature (LST), air temperature (TA), vapor pressure deficit (VPD), downward solar radiation (DSR), and fractional vegetation cover (FVC), using three representative thermal remote sensing (RS) models (STIC, TSEB, and SPARSE) together with global eddy covariance measurements.At the global scale, variance-based sensitivity analysis (Sobol' method) reveals a transition in the dominant driver of ET sensitivity from water-limited to energy-limited regimes: soil dryness (indicated by LST − TA) dominates ET variability up to an aridity index (ratio of precipitation to reference ET) of 0.54 (± 0.06), beyond which DSR becomes the primary driver. Seasonal variability and ET partitioning emphasize the critical role of soil dryness in driving soil evaporation variability, particularly during growing seasons. Furthermore, a water stress test is conducted across four representative sites with varying vegetation cover types. Results show that ET sensitivity to soil dryness nearly doubles during the drought period compared to climatological norms at the grassland site. In contrast, transpiration in forests is more strongly influenced by VPD under moderate drought stress. Analysis indicates that soil dryness generally exerts stronger control on ET than VPD. However, when vegetation cover exceeds 0.49, the influence of VPD anomalies on ET becomes comparable to soil dryness stress.This research advances our understanding of ET dynamics under increasing drought frequency and intensity. It highlights the potential of forthcoming high-resolution thermal-based RS ET products for early drought hazard warnings, climate-resilient decision-making, and sustainable agricultural water management.