Impact of time-lagging and time-preceding environmental variables on top layer soil moisture in semiarid grasslands

Top soil moisture (SM) is an important medium connecting the exchange of matter and energy between the ground and the atmosphere. Previous studies of the relationship between SM and environmental factors, especially aerodynamics, have lacked analysis of the variability in the timing of effects. In this study, we analyzed how environmental factors affect SM, as well as soil moisture memory, by observing precipitation, radiation, and wind speed during the 2019 to 2021 growing seasons in grazing prohibited and grazed areas of a semiarid grassland. The results show that there is a clear threshold (7 mm) for the effect of precipitation on SM, that changes in SM across time scales were influenced by preceding precipitation and net radiation in addition to lagging vegetation greening characteristics (NDVI) and wind speed, and that the role of albedo was related to grazing management. The inhibitory effect of albedo on SM and the depletion of SM by NDVI were more pronounced in comparison to other meteorological factors. Wind speed, precipitation, and radiation directly or indirectly influenced SM duration, and these relationships varied with grazing management and annual variation. These results help to clarify the influence of environmental factors on SM, and provide insight for minimizing the degradation of grassland ecosystems in the process of climate change.