Response of ecosystem water-use efficiency to global vegetation greening

Global vegetation has been greening during the past two decades. However, relatively less is known concerning the change of carbon–water cycle coupling in response to vegetation greening. A key indicator that can characterize this coupling is water-use efficiency (WUE) of ecosystems. Therefore, we explored the impact of global vegetation greening on ecosystem WUE using Theil-Sen trend analysis, Mann-Kendall (M−K) test, stepwise regression and Lindeman Merenda Gold model (LMG) model based on the remote sensing data from 1982 to 2018. Our results showed that global vegetation greening had a positive effect on the gross primary productivity (GPP), evapotranspiration (ET) and WUE during the past thirty years. The WUE in 70 % of these vegetation greening areas, including India, China, Russia, Japan, North Korea, Europe and North America, was increased, and the WUE was increased by 0.002 g C kg H2O yr−1, which was twice as much as that of the global vegetation cover areas. Results of stepwise regression analysis showed that vegetation greening contributed 80 % of the changes in WUE, much higher than the contribution of the climate factors. GPP contributes approximately 81 % to the changes in WUE as a result of vegetation greening. In addition, we also found that, in the greening areas around the world, leaf area index (LAI) explained 80 % of the changes in WUE, and that vegetation has a positive effect WUE. Therefore, the WUE should be considered in the design of ecological restoration programs in the future, and vegetation of low water consumption would be favored to realize sustainable ecosystem services and regional development.