Comparison of environmental controls on soil moisture spatial patterns at mesoscales: Observational evidence from two regions in China

Soil moisture plays a vital role in terrestrial water cycles, which requires the understanding of the spatial characteristics of soil moisture patterns and their influencing factors across different scales; however, inconsistent findings have been reported in the past with regards to the relative importance of meteorological (e.g., precipitation and evapotranspiration) and local (e.g., soil texture) factors in controlling soil moisture spatial variability at mesoscales. To further elucidate this issue, long-term soil moisture data from East and Northwest China were examined in this study, using two statistical methods of temporal stability analysis (TSA) and empirical orthogonal function (EOF) analysis. The TSA results showed that the spatial distributions of mean relative difference (MRD; an indicator of the relative wetness condition at a location as compared to the areal average wetness condition) of soil moisture had statistically significant correlations with mean annual precipitation (P-) and soil texture in both study regions; however, the spatial correlation between MRD and P- was much stronger in the Northwest region, suggesting that precipitation played a more important role in determining the spatial distribution of soil moisture in Northwest China. Moreover, the EOF analysis revealed that the primary soil moisture spatial structure was mostly related with soil texture in the East region while with P- in the Northwest region, which was also consistent with the TSA results. The stronger impact of precipitation on the soil moisture spatial distribution in the Northwest region could be largely attributed to the greater spatial variability in P- that varied by ~4.6 times from 171.2 to 791.0 mm/year across the region. By comparison, in the East region characterized by lower spatial variability in P- that varied by ~2.6 times from 484.2 to 1236.0 mm/year, soil texture exerted a stronger impact on the primary soil moisture spatial structure. Therefore, the observational evidence from this study demonstrated that the relative importance of meteorological and local factors in controlling mesoscale soil moisture spatial variability might vary considerably across regions, primarily depending on the spatial variability in those influencing factors across the region under consideration.