Declining soil evaporation on a drying earth

Rising vapor pressure deficit (VPD) due to warming has increased global land surface soil evaporation (E), whereas reduced soil moisture (SM) from global drying has suppressed E. However, the relative contributions of these two factors to global E remain poorly understood, creating significant uncertainty regarding its long-term trends. This study constructed an E model that integrated physical processes with machine learning and validated its performance using in-situ E data from 368 global flux sites. The trained hybrid model was then employed to create a dataset of global land surface E for both historical and future periods, enabling the identification of long-term trends and drivers of E across these timeframes. Our findings revealed that the negative impact of SM decline on global E outweighed the positive effects of increased VPD, resulting in a long-term downward trend in global land surface E from 1982 to 2023 (–0.28 ± 0.07 mm/year²). Under future climate change scenarios, global land surface E was projected to continue its decline at a faster rate than observed in historical periods (average –0.42 ± 0.11 mm/year² under three climate change scenarios from 2024 to 2100), with SM playing a dominant role in this trend. The long-term downward trend was further corroborated by nine additional E datasets. These results underscored the critical role of global drying in driving the persistent decline in global E and highlighted how climate change was exacerbating risks to global water resources.