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Vegetation change can significantly alter evapotranspiration (ET), an important component of the terrestrial water balance, and consequently influences other hydrological processes. With no direct measurement techniques available at large spatial scales, the accurate estimation of ET under changing forest landscapes and climate is challenging. In this study, we used an improved method based on Fuh’s equation (a functional form of the Budyko framework) to investigate ET responses to cumulative forest disturbance and climate in the snow-dominated interior of British Columbia, Canada. First, we divided the study region into three distinct climate groups, and then related the watershed parameter m in Fuh’s equation to vegetation change (represented by cumulative equivalent clearcut area (CECA)) and watershed properties, with independent calibration and validation watersheds. The validated relationships were used to examine regional ET variations (∼380,000 km²). Our results showed that ET in moderate climates had the highest sensitivity to CECA, characterized by wetness index between 1 and 2 (the ratio of precipitation to potential evapotranspiration). ET in dry climates (wetness index < 1) was also significantly related to CECA, but with reduced sensitivity compared to the moderate climates. Wetter climates (wetness index > 2) did not show a significant relationship with CECA, suggesting an insensitivity of ET to forest change. Simulations under future climate and vegetation disturbance scenarios demonstrated that ET would be further decreased in most of the study region. Forest management should consider reducing disturbance in the dry to moderate climate areas to mitigate negative impacts on hydrological processes and functions.

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