Unravelling the dominant controls of actual evapotranspiration in an arid inland basin: A hydrogeological gradient perspective

Study region The Manas River Basin in Northwest China represents a typical arid endorheic basin characterized by a distinct mountain-Gobi-oasis-desert continuum. However, the regulatory mechanisms of ETa spatial differentiation across this complex hydrogeological gradient have rarely been systematically analyzed. Research focus In this study, we employed a hydrogeological gradient perspective, integrating multi-source data (2000–2023) with Shapley Additive Explanations (SHAP) to disentangle the natural and anthropogenic controls on ETa along the mountain-Gobi-oasis-desert continuum. New hydrological insights ETa controls systematically shift along the hydrogeological gradient, with annual ETa peaking in the oasis (132–192 mm) and minimizing in the desert (16–60 mm). Alpine headwaters operate under an energy-limited regime, while the Gobi and desert zones are restricted by wind-driven advection and severe moisture deficits. Within the oasis zone, ETa is strictly governed by a ∼4 m water table depth threshold for natural ecosystems, beyond which fluxes precipitously decline by 30%-50%. Conversely, intensive irrigation supplants this natural constraint by maintaining soil moisture within an optimal range of 14%-16%, leading to a decoupling of crop ETa from local groundwater dynamics. This anthropogenic decoupling sustains high transpiration but incurs a severe hydrological deficit, driving progressive aquifer depletion. Synthesizing these findings, we propose a spatially partitioned conceptual model of ETa regulatory regimes that replaces generic multi-factor frameworks, thereby providing a precise physical basis for sustainable water management in arid regions.