Assessing the Impacts of Vegetation Greenness Change on Evapotranspiration and Water Yield in China

Vegetation plays an important role in regulating terrestrial water and energy fluxes. Recent research reported that China is the largest contributor to the global net increase in green foliage. Such large-scale vegetation greenness change would inevitably affect the water budget across China. In this study, we evaluated the effects of vegetation greenness change on evapotranspiration (ET) and water yield in China from 1982 to 2014 with a process-based conceptual hydrologic model and a detrending experiment of vegetation index. On the national scale, the change in vegetation greenness was dominated by an increasing trend (greening), which has led to an increase in ET and a decline in water yield from 1982 to 2014. The contribution of vegetation greenness change to the trend of annual ET and water yield is 0.25 mm/yr and -0.16 mm/yr, respectively. Spatially, the relative change in ET and runoff caused by vegetation greenness change is significantly greater in water-limited areas than in energy-limited areas. Vegetation greening exacerbated water scarcity in water-limited areas. Therefore, the ecological restoration policy should fully consider the negative effect of vegetation greening on water yield in water-limited regions and balance the conflicting water demands between the ecosystem and human beings.