Distribution of Soil Moisture over the Qinghai-Tibetan Plateau and Its Effect on the Precipitation in June and July over the Mid-Lower Reaches of Yangtze River Basin
Soil moisture has been widely recognized as one of the main drivers of the water and carbon cycle in the climate system. It plays an important role in the interactions between the atmosphere and the land surface with climate change through its influence on the surface albedo and vegetation. To understand the temporal and spatial distribution of soil moisture over the Qinghai-Tibetan Plateau and its influence on the precipitation in the mid-lower reaches of Yangtze River Basin, with monthly dataset of soil moisture derived from Climate Prediction Center (CPC) and monthly precipitation obtained from National Meteorological Information Center (NMIC) of Chinese Meteorological Administration (CMA) from 1961 to 2014, the distribution of soil moisture over the Qinghai-Tibetan Plateau has been investigated along with its effect on the precipitation in June and July over the mid-lower reaches of Yangtze River Basin. Result shows that seasonal distributions of soil moisture are consistent with the annual distribution and the soil moisture decrease from the southeast part to the northwest part of the Qinghai-Tibetan Plateau. The regional soil moisture presents that it is extremely dry in spring while the moisture is quite humid in autumn and summer over the plateau. Considering the most parts of the plateau, the annual and seasonal soil moistures exhibit slightly increasing trend during the past 50 years. The annual and the seasonal soil moisture basically indicate decreasing trend from 1960s to 1990s, and they increase gradually with small magnitude from twenty-first century to the present years. The precipitation in the mid-lower reaches of Yangtze River Basin is negatively related to the spring soil moisture over the plateau. The negative relation areas which exceed the significance level are mainly located in the northeast and southwest parts of the plateau in June. The negative areas are situated in the southern plateau while the positive areas are located in the northwest part of the Plateau in July. The spring soil moisture is contributed to the precipitation distribution in the mid-lower reaches of the Yangtze River Basin by means of its effect on the surface temperature, atmospheric circulation and thermal forcing over the Plateau. The spatio-temporal distribution of soil moisture and the correlation between spring soil moisture over the Qinghai-Tibetan Plateau and subsequent precipitation in the mid-lower reaches of Yangtze River Basin are investigated with soil moisture derived from CPC and precipitation from CMA. The impact of soil moisture on seasonal precipitation and its possible mechanism will be the subject of a future study.