A Comparative Study of Multi-source Soil Moisture Data for China's Regions

Based on observational data of soil humidity from 1992 to 2010 in China's regions, this study evaluated the reliability of soil humidity data in typical regions collected via satellite remote sensing and inversion by the European Space Agency (ESA), and reanalysis by the European Centre for Medium-Range Weather Forecasts (namely, the ERA-Interim reanalysis, hereinafter referred to simply as ERA). The results indicated that these two kinds of soil humidity data can describe the overall change in soil humidity well in these regions, but the mean of the data and the trend differ both temporally and spatially. Data from ESA and ERA can describe the distribution pattern of soil humidity well in spring, summer, and autumn in China's regions. When compared with the observational humidity data, the ESA data showed soil to be less humid in the northern region and more humid in the Yangtze-Huaihe region and southwestern region. Meanwhile, the ERA data showed soil to be more humid in the northern and southwestern region and less humid in the Yangtze-Huaihe region. In part of the Yangtze-Huaihe region and northern region, the correlation between the ERA and observational data was higher than that between the ESA and observational data. The correlation of the ESA and ERA data with the observational data was best in autumn (most stations' correlation coefficients were above 0.7). In most regions of China, ESA's deviation was less than that of ERA, but they both showed the same trend of change as the observational data in most regions. In spatial terms, the scope of the change trend of the ERA data in the northeastern region, northern region, and southwestern region was obviously different from that illustrated by the observational data: The region with decreasing moisture was obviously larger than that according to the observational data, but the ERA data better reflected the interannual change in soil humidity. Compared with western regions, ERA in eastern regions was more consistent with observations, while in periods or regions where ESA was less influenced by such factors as rain, vegetation and topography, ESA was more consistent with observations and could reflect soil humidity more precisely in autumn than in spring and summer.