Potential of global land water recycling to mitigate local temperature extremes

Soil moisture is projected to decrease in many regions in the 21st century, exacerbating local temperature extremes. Here, we use sensitivity experiments to assess the potential of keeping soil moisture conditions at historical levels in the 21st century by “recycling” local water sources (runoff and a reservoir). To this end, we develop a “land water recycling” (LWR) scheme which applies locally available water to the soil if soil moisture drops below a predefined threshold (a historical climatology), and we assess its influence on the hydrology and extreme temperature indices. We run ensemble simulations with the Community Earth System Model for the 21st century and show that our LWR scheme is able to drastically reduce the land area with decreasing soil moisture. Precipitation responds to LWR with increases in mid-latitudes, but decreases in monsoon regions. While effects on global temperature are minimal, there are very substantial regional impacts on climate. Higher evapotranspiration and cloud cover in the simulations both contribute to a decrease in hot temperature extremes. These decreases reach up to about −1 ∘C regionally, and are of similar magnitude to the regional climate changes induced by a 0.5 ∘C difference in the global mean temperature, e.g. between 1.5 and 2 ∘C global warming.