Distribution And Temporal Change Of Surface Soil Moisture In The Yellow River Basin

Soil moisture is an important component of soil, affecting not only soil properties and vegetation distribution but also rainfall infiltration before runoff begins. Most areas of the Yellow River Basin are located within the semi-humid, semi-arid or arid climate areas. Study on surface soil moisture in this area is of significance as severe soil erosion problems. Using surface soil moisture data of the ERS scatterometer and precipitation data, this study explored the difference of surface soil moisture within agricultural zones and forestry zones during similar precipitation conditions. Besides, the spatial distribution, seasonal and inter-annual variation of surface soil moisture has been analysed on the basis of surface soil moisture content, which is calculated from soil distribution and moisture properties of different soils, in the Yellow River Basin from 1992 to 2000.The major results are shown as follows:(1)Impacted by precipitation, the response of surface soil moisture index in agricultural zones is quicker, and so as the surface soil moisture content, which causes soils here are easier to become saturated than them in forestry zones. At the same time, it takes approximately ten more days for forestry zones than agricultural zones to reach certain surface soil moisture situation if the original surface soil moisture index is same after precipitation. In other words, in ten days, loss of soil moisture in forest is only 50 % of that in agriculture lands in extremely case. That is to say, soil moisture loss in agricultural areas is faster than in forestry areas. Soil surface in agriculture lands is more vulnerable to drying.(2)Soils in the Yellow River Basin could be categorized into four classifications and their textures are composed mainly with sandy soil, loam, clay loam and clay, out of which loam soil is the most widespread, accounting for 57.6 % of Yellow River Basin area. The following type is sandy soil accounting for 30 % of the basin. According to the different soil moisture porosity, moisture absorption coefficient, surface soil moisture volume is calculated from SSM of Yellow River Basin.(3) Several sites are relatively wetter, such as in the Source Region of the Yellow River, Ordos Region, the south of the Loess Plateau Area and Lower Course area of Yellow River. Among these areas, the Source Region of the Yellow River contain the relatively highest surface soil moisture content. In addition, soil moisture in Ordos Region, the south of the Loess Plateau Area and Lower Course area of Yellow River is higher than that in the surrounding areas in the most period of one year. The drought areas of the Yellow River Basin are mainly concentrated in the Mu Us Desert and the Endorheic Region. Other areas except the Source Region of the Yellow River, the surface soil moisture increased gradually from the northwest to the southeast.(4) The surface soil moisture inter-annual variation of the Source Region of the Yellow River is small. The surface soil moisture inter-annual variation of the Mu Us Desert and the Endorheic Region is not remarkable, but the surface soil moisture is always below 15%. The surface soil moisture inter-annual variation of the south Loess Plateau Area and Lower Course area of Yellow River is more higher.