Spatial-temporal Variation of Soil Moisture and its Possible Impact on Regional Climate in China

Soil moisture is a connection among the atmosphere, hydrosphere, and biosphere, which makes it one of the most significant climate variables. Using data from the National Environmental Forecasting Center (NCEP), this paper analyzed the temporal and spatial characteristics of soil moisture at a depth of 0-10cm in China for the period from 1948 to 2014 and explore the soil moisture's possible interaction with air temperature. The results showed that, the annual soil moisture in China displayed a sandwich distribution, with relatively low-value areas concentrated in the northwest China and the north China and with relatively high-value areas in the south China, the southeast China, the Tibetan Plateau and the northeast China. During this period, annual soil moisture decreased significantly (P <0.01) in most regions except for the south China. The tendency to decrease was relatively greater in spring and autumn than that in summer and winter, with the most significant trend appearing in central China in spring, north China in summer, and northeast China in autumn. As for the national annual average soil moisture, there was an abruption in 1970s, and before it happened, the soil moisture tended to have a relatively high value with a larger deviation, but after the abruption the soil moisture remained a relatively low level with a smaller deviation. Most regions showed a slackened decrease, but in certain places the soil water deficit situation intensified. It was found that the soil moisture at 0-10 cm showed a good correlation with 2-meter air temperature above the ground. The correlations between annual soil moisture and air temperature differed from region to region. It appeared that, in most regions they had negative correlation. And there was a significant negative correlation in the northeast China, central China and east China, where agricultural activities intensity were relatively high. These results had significance in understanding the role of soil moisture in temperature rising especially in regional scale.