Recent change in ecosystem water use efficiency in China mainly dominated by vegetation greening and increased CO2

Over the last two decades, the significant vegetation increase caused by the execution of several ecological restoration programs has modified the integrated carbon and water cycles. However, the underlying mechanisms of ecosystem water-use efficiency (EWUE) change remain unclear. The current study estimates the annual and seasonal variations in the spatiotemporal patterns of EWUE from 2000 to 2018 and quantifies its driving factors to distinguish the impacts of vegetation and environmental factors across China. The contribution of driving factors to EWUE dynamics is quantified using PML_V2 gross primary productivity (GPP) and evapotranspiration (ET) products by employing the partial derivative (PD) equation. The results reveal that the leaf area index (LAI) is the major contributor in altering the EWUE of China, followed by CO2. The mean seasonal contribution of LAI is dominated by summer (0.0044 gC mm−1H2O yr−1) and spring (0.0035 gC mm−1H2O yr−1), followed by winter (0.0029 gC mm−1H2O yr−1) and autumn (0.0013 gC mm−1H2O yr−1), while the annual contribution is calculated to be 0.0017 gC mm−1H2O yr−1. The rate of CO2 contribution to EWUE was highest in spring (0.0022 gC mm−1H2O yr−1), followed by winter (0.0012 gC mm−1H2O yr−1), autumn (0.001 gC mm−1H2O yr−1) and summer (0.0007 gC mm−1H2O yr−1), while the annual rate was calculated to be 0.001 gC mm−1H2O yr−1. The relative contribution of climatic factors is the most considerable in the summer season, with 8.6%. The negative contribution of CO2 to EWUE along south China coast may not be influenced by CO2, rather because of the seasonal variations in GPP and ET trends. Our findings suggest that vegetation greening taken place in the last couple of decades has significantly enhanced EWUE trends in China and could help to develop future ecological restoration programs considering EWUE variations for effective ecosystem management and efficient water use.