# Analyzing the Characteristics of Soil Moisture Using GLDAS Data: A Case Study in Eastern China
## 1 Introduction  
Soil moisture plays a very key role in the process of climate evolution. It not only carries the responsibilities of energy and water exchange between land and atmosphere, it also takes part in the land-atmosphere interaction. As to be explained, soil moisture and climate changes are connected. Soil albedo, soil heat capacity, and the transfer of heat into the atmosphere are affected by changes in levels of soil moisture, which indirectly affects climate change. Climate change will also have an impact on the soil by altering its moisture content. For example, although the heat capacity of soil is small, surface albedo is large; yet the transfer of heat into the atmosphere is not obvious for small soil moisture. In different soil moisture areas, the form of interaction is not the same [1,2]. Because of deep soil's vertical direction, precipitation's effects on its soil moisture lags by about 1 to 2 months. Consequently, climate change is also influenced by future soil moisture [3]. Similarly, the evolution of soil moisture is mainly affected by the properties of soil, the strength of the light, the moisture of the air, and wind speed. The evolution of soil moisture is particularly affected by temperature and precipitation. As soil moisture plays a critical role in the evolution of climate, soil moisture is the first factor considered [4, 5, 6, 7]. The research into the climate evolution of soil moisture is still limited by the varying length of observation data and influence of the area. Remote sensing [8, 9] observes the large-scale coverage, but it is very dependent on the inversion algorithm and deep soil moisture cannot be inverted. The researchinto soil moisture using remote sensing observation is therefore limited. With the development of the numerical model [10], it became possible to analyze soil moisture evolution characteristics on a regional scale and an inter-annual scale. Yet the initial value set affects whether the final results are determined correctly. The emergence of a global land data assimilation system overcomes the remote sensing observation's dependence on the inversion algorithm and numerical models for the accuracy of results. Comparing the land data assimilation system with other simulation models, the advantage of GLDAS's data is that it is closer to the actual situation [11] and the results also more in line with the actual standard. At present, although GLDAS outputs can be highly uncertain [12; 13] and data validation with in situ observations is generally necessary, their unique characteristics also fit many different models [14; 15; 16]. Previous studies reported that the change of soil moisture in eastern China is active [17], while the mutual influence of each circle in eastern Asia is very positive. The weather evolution, especially the generation and evolution process of a monsoon, is greatly affected by soil moisture. An analysis of the strong coupling areas of soil moisture and precipitation [17] through the global land-atmosphere coupling experiments established that soil moisture is very sensitive to precipitation. By adding the soil moisture assimilation data to the simulation values of temperature and precipitation in eastern China [18], temperature and precipitation simulation values become closer to observed values, which means that soil moisture has a certain impact on temperature and precipitation. The soil moisture data from regions within China can be used to analyze the radial evolution characteristics of soil moisture [19], revealing the inter-annual variability of soil moisture vertical distribution regularity and its relationship with precipitation. Furthermore, when combined with the observed data on soil moisture in eastern China [20], the evolution law of soil moisture and the relationship between soil moisture and climate change rates clearly show a positive correlation between precipitation and soil moisture, whereas the correlation between temperature and soil moisture is negative.