Analysis on Soil Moisture Content in the Middle Reaches of the Yellow River

In this paper,the data of soil moisture content in the middle reaches of the Yellow River during the period of 1981-2002 were analyzed to find the horizontal and vertical distribution laws. Characteristics of interannual and inter-decadal change of soil moisture content were also analyzed. The results reveal that,horizontally,soil moisture content was approximately higher in the central part than that in the southwestern and southeastern parts of the study area. Vertical distribution of soil moisture content changed seasonally. Soil moisture content was sharply decreased from early spring to May,especially in topsoil,the time when soil became the driest was earlier for 3 ten-day periods than that in soil layer of 50-100 cm,and the upper soil layer was drier than the lower one. Moisture content in topsoil was sharply increased in rainy season,and it was higher than that in lower layer. Holistically,soil moisture content was in a decrease trend,and there was a 5-6-year periodic change in the study area during the period of 1981-1996. There was an abrupt change of soil moisture content around 1991 in the central-southern part. Soil moisture content and its interannual change extent were high before 1991,and then soil became drier and the interannual change extent was lower. The change of soil moisture content was the most remarkable in the central-southern part of the study area.