Anthropogenic Impacts on the Water Cycle over Drylands in the Northern Hemisphere

The effects of anthropogenic factors on the water cycle in drylands of the Northern Hemisphere (NH) are unclear. Here, we used the Community Earth System Model (CESM2.1.0) to quantify the influences of greenhouse gases (GHGs) and anthropogenic aerosols (AAs) on the water cycle and precipitation recycling rate (PRR) over drylands from 1980 to 2014. The corresponding mechanisms are also revealed in this study. The results show that GHGs can intensify the water cycle over drylands by increasing precipitation (P; 0.023 mm day-1) and evapotranspiration (ET; 0.037 mm day-1). Consequently, the negative P -ET (-0.014 mm day-1) is induced because infiltration (I;-0.014 mm day-1) and total water storage (S;-0.011 mm day-1) are decreased, implying a loss of soil water. The PRR is reduced by approximately-0.18% because of the GHG-induced extra water vapor export, which originated from ET. In contrast, AAs can weaken the water cycle over drylands by decreasing P (-0.03 mm day-1) and ET (-0.039 mm day-1). Correspondingly, positive P -ET (0.009 mm day-1) is induced, reflecting an input of soil water. Because of the AA-induced persistent ET from a wetter land and the reduced export water vapor from ET, the PRR increases by approximately 0.15%. Mechanistically, GHGs and AAs can affect the water cycle over drylands by perturbing the descending branches of Hadley circulation in midlatitude regions. Quantifying the climate effects of GHGs and AAs on the regional water cycle improves our under-standing of the regional water cycle; the results of this study could also be conducive to the climate predictions for drylands.

Automated summary

This study used the CESM2.1.0 model to investigate the effects of greenhouse gases and anthropogenic aerosols on the water cycle and precipitation recycling rate in drylands from 1980 to 2014. The results showed that greenhouse gases intensified the water cycle by increasing precipitation and evapotranspiration, leading to a decrease in soil water and a reduction in precipitation recycling rate. On the other hand, anthropogenic aerosols weakened the water cycle by decreasing precipitation and evapotranspiration, resulting in an increase in soil water and an increase in precipitation recycling rate.