Variation in vegetation water use efficiency at the basin scale: separating the contributions of climate change and human activities

Water use efficiency (WUE) is an important indicator for the characterization of the regional carbon–water interaction. Understanding the influence of climate change and human activities on it is essential for terrestrial ecosystems and water management. In this study, we selected the Tao river basin in northwestern China as an example to quantify the impacts of climate change and human activities on the variation of regional WUE from 1982 to 2015. Results revealed that: (1) WUE values ranged from 0.54 to 3.14 g C kg −1 H 2 O across the basin, fluctuated with an overall increasing trend during the statistic time period, more remarkably in the area of downstream. (2) The influence of the actual evapotranspiration on ∆WUE was more notable in the up- and midstream, while the gross primary productivity dominated ∆WUE downstream, the contributions of both across the basin were quantified at 88.19% and 11.81%. (3) ∆WUE due to climate change and human activities were estimated at multi-yearly averaged values of 0.05 and − 0.03 g C kg −1 H 2 O, respectively. The positive effect of climate change imposed on WUE occurred more in the downstream, while the negative effect of human activities occurred more in the midstream. Overall, the relative contribution rates of climate change and human activities to ∆WUE were 0.62 and − 0.38 across the whole basin, respectively, during the time period from 1982 to 2015. The study provided a case example to understand the WUE variation in diverse geo-ecological regions across large river basins.