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 modelling 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; 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.

全球变暖改变了地表水的可用性（降水减去蒸散，P-E），从而改变了淡水资源。然而，陆地-大气反馈对未来 P-E 变化的影响及其潜在机制仍不清楚。在这里，我们证明了土壤水分（SM）通过调节蒸散和大气水分流入，强烈影响未来的 P-E 变化，特别是在旱地。使用建模和经验方法，我们发现 P-E 上存在一致的负 SM 反馈，这可以抵消大约 60% 的旱地 P-E 下降，否则在没有 SM 反馈的情况下是预期的。负反馈不是由大气对 SM 下降的热力学响应引起的；相反，减少 SM，除了限制蒸散，调节大气环流和垂直上升，以增强水分向旱地的输送。这种 SM 效应是预测的旱地 P-E 变化的一个很大的不确定性来源，强调需要更好地约束未来的 SM 变化并改进模型中 SM 大气过程的表示。