Ecozone–dependent reorganization of multifactor interactions controls actual evapotranspiration across arid mountain–basin systems

Actual evapotranspiration (ETa) is a key regulator of land–atmosphere water and energy exchanges in arid regions. However, the coupled effects of its controlling factors along mountain–basin gradients remain poorly quantified, limiting precise water resource management. Based on multi-source data (2001–2022) from Xinjiang Uygur Autonomous Region, China, this study analyzed the spatiotemporal patterns of ETa across five eco-zones: the Altay Mountains, Junggar Basin, Tianshan Mountains, Tarim Basin, and Kunlun Mountains. Using Mann–Kendall and Theil–Sen trend analyses, GeoDetector, and Random Forest model, we quantified the contributions and interactions of seven environmental drivers: air temperature, precipitation, soil moisture, wind speed, net radiation, vapour pressure deficit, and leaf area index. The multi-year mean ETa over Xinjiang was 193.15(±21.16) mm/a, showing a distinct ''high in mountains and low in basins'' spatial pattern. A significant increasing trend of 1.60 mm/a was observed regionally, yet with clear spatial divergence, i.e., ETa increased in the major mountain ranges but decreases or stabilized in the hyper-arid Tarim Basin and transitional Junggar Basin. Water-supply factors (precipitation and soil moisture) explained about 40% of the spatial variance individually, while factor interactions enhanced the explanatory power substantially (maximum interaction gain (Δ q )=0.18), indicating that bivariate and nonlinear combinations captured ETa patterns more effectively than single driver. Interaction regimes were strongly ecozone-dependent and varied between wet and dry years. Through comparing the wet year (2003) with the dry year (2022), we found a reorganization of dominant interaction pairs: the hyper-arid Tarim Basin shifted from hydrothermal control to vegetation–water-stress coupling; the Junggar Basin maintained persistent vegetation–energy coupling; the Altay and Tianshan Mountains strengthened vegetation-mediated interactions during drought; and the Kunlun Mountains transition from hydrothermal to moisture–aerodynamic control. These results clarify how complex topography and vegetation physiology modulate macroclimatic forcing in this arid mountain–basin system. These findings offer a process-based foundation for ecohydrological zoning, and provide critical insights for adaptive water ecosystem management and sustainable development in response to the "warming and wetting" trend in global drylands.