Enhanced effects of changes in precipitation on the water yield and ecosystem sustainability

Predictions of climate change over land indicate drying trends in the form of ecological and agricultural droughts over many regions (1-6), and increased flooding in others (7). Globally, evapotranspiration (ET) from vegetated areas consumes about 63% of annual precipitation8, which is expected to increase with global warming (9,10), and can approach 100% in drylands (11) beyond which ecosystems are unsustainable. As global climate change progresses, it remains unknown what fraction of the precipitation will remain available for runoff, recharge of aquifers and consumption, or prevent ecosystems’ collapse in dry regions (7,12). Here, we show using a global dataset that evapotranspiration from ecosystems displays a conservative ‘saturation effect’ at ~460 mm across climates with a precipitation range of ~4000 mm. This implies that changes in precipitation are preferentially reflected in ecosystem water yield (WY; the residual between precipitation and evapotranspiration). Consequently, changes in WY are greatly enhanced compared with precipitation changes, both in observations and model-based future projections. In dry regions, ecosystems will reach the unsustainable state (negative WY) faster than expected based on predicted changes in precipitation alone, imposing land cover changes and impacting water availability for ecological and societal needs.