Spatial heterogeneity and explanatory variables of surface soil moisture changes in the Northwest Shandong Plain, China

This study explored the spatial variability of surface soil moisture (SSM) and its explanatory variables during distinct monsoon periods in the Northwest Shandong Plain using geo-statistical techniques and the Optimal Parameters-based Geographical Detector (OPGD) model. The findings reveal significant seasonal differences in SSM spatial patterns, with higher heterogeneity in summer (CV = 72.41%) compared to winter (CV = 17.91%). Soil salinity and electrical conductivity are the primary drivers of SSM variability, explaining up to 85% and 75% of summer variation, respectively, and 60% and 62% in winter. Vegetation cover has a stronger influence in summer (q = 0.30), while topographic factors such as elevation (q = 0.40) and aspect (q = 0.35) dominate in winter. The OPGD model identifies complex, nonlinear interactions, with slope-salinity (q = 0.94) and slope-conductivity (q = 0.89) as the strongest in summer and winter, respectively. This study highlights the seasonal variability of SSM heterogeneity in semi-humid regions and demonstrates the effectiveness of the OPGD model in analyzing nonlinear relationships.