Spatiotemporal patterns of water use efficiency in China and responses to multi-scale drought

Drought is a natural disaster that profoundly affects the carbon and water cycles in terrestrial ecosystems. Quantifying the responses of terrestrial carbon and water cycles to drought is crucial for assessing the impacts of climate variability on these ecosystems. Using Moderate Resolution Imaging Spectroradiometer gross primary productivity (GPP) and evapotranspiration (ET) products, this study evaluated the spatiotemporal patterns and trends of water use efficiency (WUE) for China's terrestrial ecosystems from 2000 to 2014 and analyzed their responses to multi-scale drought across different river basins, vegetation types, and climatic zones. The key findings are as follows: (1) The annual WUE in China's vegetated areas has significantly increased at a linear rate of 0.01/gC kg(-1) H2O a(-1) (P < 0.05). (2) The spatial patterns of average annual WUE in China's vegetated areas had large spatial variability. Higher average annual WUE values were found in the basins with high forest or cropland coverage and within humid climatic zones. Lower average annual WUE values were found in the basins with high grassland coverage and within arid and semi-arid climate zones. In total, 40.59% of the WUE in China's vegetated areas significantly increased (P < 0.05). They were mainly distributed in Northern China. (3) From 2000 to 2014, WUE values in 32.79%, 7.21%, 23.33%, and 8.57% of the China's vegetated areas were highly sensitive to drought in the growing season, spring, summer, and autumn, respectively. (4) The growing season, summer, and autumn had significantly higher correlations (P < 0.05) over the Standardized Precipitation and Evapotranspiration Index-24 time scale than those over the other time scales. (5) During the growing season, WUE values in river basins with a humid climate and forest coverage were more sensitive to drought than to other river basins.