Dynamics and interactions of soil moisture and temperature in semi-arid regions of northern China

This study investigated the hydrothermal coupling and the effects of land use changes in the semi-arid regions of northern China (SANC). Using the ERA5-Land dataset spanning from 1981 to 2020, we analyzed soil moisture (SM) and temperature (ST) patterns. Our analysis involved a comprehensive examination of these patterns and their interactions, along with the influence of land use alterations. The results indicate a spatial distribution of SM, characterized by diminished levels in the northeast and elevated levels in the southwest. Over a span of 40 years, SM diminished markedly (0.005 m³/(m³·10a), P < 0.01), whereas ST escalated (0.26 °C/10a, P < 0.01). Alterations in land use, especially the expansion of cropland at the detriment of forests and grasslands, have profoundly influenced soil hydrothermal dynamics. SM decreased more swiftly, and ST increased more rapidly in agricultural and urban regions. A negative correlation was observed between SM and ST, particularly in arid regions with positive heat budgets, underscoring the regulatory function of SM. In humid regions with negative heat budgets, there was a positive correlation, wherein SM affected heat fluxes and moderated temperatures. These findings are essential for enhancing climate models, water management, and adaptation strategies in these at-risk ecosystems.