Enhanced effects of declining precipitation on the water yield and ecosystem sustainability

Climate change is predicted to change precipitation (P) and evapotranspiration (ET) over most land areas, imposing substantial pressure on water supply in some parts, while increasing flooding in others. Our global dataset shows that ET from ecosystems displays a conservative ‘saturation effect’ at ~460±190 mm across climates with P range of ~4000 mm. This implies that changes in P are preferentially reflected in the residual ecosystem water yield (WY=P-ET). Consequently, changes in WY are greatly enhanced compared with those in P both in observations and in model-based future projections. In drying regions, ecosystems will reach the unsustainable state of WY<0 faster than expected based on predicted changes in P alone, imposing land cover changes, and impacting water availability for ecological and societal needs.