Global warming is expected to change surface water availability and freshwater resources, but the influence of ecosystem feedbacks remains poorly known. We find a large soil moisture feedback strongly impacts future surface water changes, particularly in drylands.
Our study provides the first evidence that soil moisture feedbacks will strongly affect dryland water resources. We show that these feedbacks ameliorate projected dryland surface water availability declines. Accounting for feedbacks is therefore essential for reliable projections of future earth system dynamics.
Global warming alters surface water availability (precipitation minus evapotranspiration, P-E) and hence freshwater resources. However, the influence of land-atmosphere feedbacks on future P-E changes and the underlying mechanisms remain unclear. Here we demonstrate that soil moisture (SM) strongly impacts future P-E changes, especially in drylands, by regulating evapotranspiration and atmospheric moisture inflow. Using modeling and empirical approaches, we find a consistent negative SM feedback on P-E, which may offset ~60% of the decline in dryland P-E otherwise expected in the absence of SM feedbacks. The negative feedback is not caused by atmospheric thermodynamic responses to declining SM but rather reduced SM, in addition to limiting evapotranspiration, regulates atmospheric circulation and vertical ascent to enhance moisture transport into drylands. This SM effect is a large source of uncertainty in projected dryland P-E changes, underscoring the need to better constrain future SM changes and improve the representation of SM-atmosphere processes in models.