Spatio-temporal variations in water use efficiency and its drivers in China over the last three decades

Abstract Ecosystem water use efficiency (WUE) reflects the intimately coupled relationship between the carbon and water cycles in terrestrial ecosystems. However, the inter-annual variation and its drivers of WUE are poorly understood at regional/global scale, due to either limited data availability or uncertainties in current data streams. In this study, we used process-based models simulated gross primary productivity (GPP) and evapotranspiration (ET) data to estimate the ecosystem WUE (eWUE, GPP/ET) in China for 1979–2012. The eWUE estimates were validated against eddy covariance-based values from 35 flux towers. The inter-annual variation of the eWUE was quantified and its responses to annual precipitation (AP), annual mean temperature (AMT), and annual mean leaf area index (AMLAI) were analyzed. The key findings were as follows. (i) The mean annual eWUE over China was 1.48 ± 1.04 g C kg −1 H 2 O and had a slightly increasing but not significant trend (7.32 × 10 −4  g C kg −1 H 2 O yr −1 , p p