Analysis of spatiotemporal characteristics of surface soil moisture across China based on multi-satellite observations

As a key state variable, soil moisture influences hydrological, meteorological and ecological processes. The objective of this study is to study the spatiotemporal characteristics of surface soil moisture across China using multi-satellite observations and uncover the driving forces of these characteristics. We applied an ensemble average approach to derive daily surface soil moisture with a spatial resolution of 25 km across China from 2015 to 2016 from five satellites, including SMAP, SMOS, AMSR2, FY3B, and FY3C. Uncertainty in these satellite products and their differences were further quantified by intercomparison. The spatial distribution of surface soil moisture and its connection with the spatial distribution of hydroclimatic zones were also analyzed. The correlations of soil moisture with precipitation and actual evapotranspiration were studied, too. The results show that spatial distribution of soil moisture across China corresponds well with the distribution of hydroclimatic zones:soil moisture generally increases from the northwest of China to the southeast and northeast of China. Clear seasonality appears in most areas of China with higher values in summer and lower values in winter. However, the amplitude and shape of seasonality differ in different parts of China. Temporal variabilities of soil moisture in over 60% of China are strongly controlled by the synchronous and antecedent precipitations. In over 87.5% of China, soil moisture and actual evapotranspiration show significant positive correlations and mutual dependence.