Temporal and spatial features of the soil moisture in boreal spring in eastern China

Soil moisture data of 45 years from European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the in situ observational data are used to study the temporal and spatial characteristics of the soil moisture in boreal spring in the area to the east of 100A degrees E in China. Results show that ERA-40 soil moisture well reproduces the temporal and spatial features of observations. ERA-40 data capture the spatial pattern that the soils in Northeast China and Southwest China are wetter than those in Inner Mongolia and North China and represent the inter-annual variability in observations. The dry trends of spring soil moisture are evident over the whole eastern China. It is especially prominent for the dry trend in southwest China where the spring soil from surface to deep-layer show drying and the trend became significant after the 1980s. The dry trend in Northeast China is weak after early 1970s in near-surface layer but aggravates after latel 1970s in deep layers. In the mid-latitude zone, the inter-annual variation of spring soil is robust and shows no dry trend except in deep-layer after 1988.