Analysis of the Spatiotemporal Distribution Patterns and Heterogeneity of Soil Moisture Based on Automatic Measuring Station in China

The spatial-temporal distribution and variability of soil moisture (SM) constitutes a critical foundation for coordinating agricultural productivity, ecological preservation, and mountain flood disaster mitigation. Based on observed SM data from 27 automated monitoring stations established by the Aerospace Information Research Institute during 2022-2024 across different climatic zones in China, the temporal change patterns, spatial heterogeneity characteristics, dominant meteorological influencing factors and the respective quantitative contributions, as well as the time-lagged responses to meteorological variables in different climatic zones were analyzed systematically applying integrated methodologies combining the regional spatial-temporal analysis, principal component analysis, random forest algorithm and cross-correlation techniques. Temporally, the monthly SM in all climatic zones exhibited consistent seasonal patterns characterized by higher values in spring-summer and lower levels in autumn-winter. Notably, the tropical monsoon and subtropical monsoon climate zones displayed lower variability in monthly soil moisture fluctuations, whereas the temperate monsoon, temperate continental, and alpine plateau climate zones manifested various seasonal divergence. Spatially, the annual and seasonal SM exhibited a declined characteristic from southeastern to northwestern regions. Conversely, the coefficient of variation of SM presented an inverse pattern with enhanced variability along the same direction. Generally, the relationship between SM and soil depth was optimally modeled closely aligned with quadratic regression, demonstrating both initially increasing and then slightly decreasing trend and monotonically increasing trend with increasing depth. The meteorological variables on SM ranked the descending order of significance were mean temperature, maximum temperature, minimum temperature, precipitation, net solar radiation intensity, and mean wind speed. Simultaneously, the minimum temperature emerged as the highest contribution to SM in different soil layers. The meteorological forcing contributions in different climate zones displayed significant spatial heterogeneity affected by soil texture, vegetation type and topography. Meanwhile, the hydroclimatic response mechanisms were found that the temperature exhibited prolonged time-lagged effects on SM ranging from 21 to 101 days, whereas the precipitation manifested rapid coupling with merely 2 to 6 days.