Study on Spatiotemporal Variation of Soil Moisture in China in the Past 71 Years

Soil moisture is a comprehensive reflection of soil moisture status and is an important parameter for land surface conditions. Studying the distribution characteristics of soil moisture is important for protecting the ecological environment and scientifically and rationally using soil water resources for climate research. Based on the v2.0 and v2.1 soil layer moisture data sets combining GLDAS and Noah models, this paper analyzes the spatial-temporal distribution of soil moisture in China from 0 to 200 cm layer-by-layer in the nearly 71 years from 1948 to 2018 with pixels as the basic object. The Mann-Kendall trend test was used to explore the change trend of soil moisture and its spatial variation in the past 71 years, and calculated the coefficient of variation of soil moisture in each pixel to analyze the temporal and spatial fluctuations of soil moisture in the entire study area during the 71 years. Finally, the Hurst index was used to predict the future trend of soil moisture changes in each layer. In addition, the correlation between soil moisture and the spatiotemporal variation of soil temperature in China was explored. Through the above data statistics and analysis, new spatial-temporal variability characteristics of soil layer humidity of $0 \sim 200$ cm in China were found: the four-layer soil layer humidity has a consistent trend over the years, that is, the soil humidity in most parts of the east is decreasing, especially in Northeast China, Central China, the surrounding areas of the Yunnan-Guizhou Plateau, and Taiwan Island, while most of the western regions are in an increasing trend; the change of soil layer humidity from 0 to 200cm in southern China is more dramatic than that of the northern region, and the humidity of the soil layer in the Pearl River Delta region is the most unstable; the spatial variation of soil moisture in the study area over the years was relatively small from 1948 to 2001, from 2002, the soil moisture in each area of the study area became uneven every year; in the future, the soil moisture change trend in most areas of China will still be consistent with the change trend in the past 71 years, the soil in most parts of the east will gradually dry out, and the soil moisture in most parts of the west will gradually increase; most of the soil layer humidity from 0 to 200 cm in the study area is inversely related to soil temperature, and is mainly concentrated in the northeast, central China, central and northern Inner Mongolia, the Qinghai-Tibet Plateau, and Taiwan Island.