Climate Regulates the Effects of Abrupt Vegetation Shifts on Soil Moisture in the Loess Plateau, China

ABSTRACT Abrupt vegetation shifts, defined as an abrupt and irreversible level shift in the intercept (rather than slope) in productivity, indicate transitions of unstable ecosystems to alternative states. Understanding these shifts is critical when monitoring ecosystem productivity because they may reveal drivers and environmental impacts that differ from gradual changes in vegetation. In China's Loess Plateau where sustainable water resource limits are being approached due to revegetation, it is unclear whether large‐scale abrupt vegetation shifts have occurred and how the various vegetation changes have affected the soil water content (SMC). In this study, we found that approximately 27.9% of grasslands and 24.8% of forests on the Loess Plateau experienced positive abrupt vegetation shifts from 2000 to 2020. The results of the climate zone method and the multi‐period difference‐in‐differences (MDID) model showed that the effects of abrupt vegetation shifts on the SMC vary geographically. Approximately 55.9% of grasslands and 33.9% of forests can wet the soil (0–289 cm) during abrupt greening, while 35.7% of grasslands and 37.6% of forests may cause drying in such events. Positive hydrological responses of soil to vegetation greening were concentrated in grasslands with precipitation below 340 mm and forests with precipitation below 520 mm, and this could be related to the limitation of lower precipitation on evapotranspiration. Similar positive responses were also found in strong evaporative environments where the temperature, solar radiation, and wind speed were higher, and the vapor pressure deficit was lower, which may have been associated with the constraints of soil evaporation through vegetation greening. This study reveals the existence of spatial heterogeneity in the hydrological response of soils to abrupt vegetation shifts and explores possible climate‐regulating mechanisms. The results could be used to inform the development of targeted conservation and restoration measures in areas with similar climate conditions.