| Soil water is one of the most important components of soil, it plays a very important role in the process of soil formation, at the same time, the soil water is involved in the transformation process of many substances in the soil to a large extent. Moreover, soil water is the main source of crop water, provide water for crop growth, and is one of the most important parameters for the agriculture, meteorology and hydrology studies. Soil water is a necessary condition for agricultural production, especially in the arid and semi-arid area, and has important significance for the rained agriculture and vegetation growth. As the important agricultural regions in China, in addition to the precipitation recharge, soil water in North China Plain(NCP) is also largely affected by irrigation, therefore irrigation has become main limiting factors restricting the growth of the crops. How to monitor and analyze surface soil moisture, drought and irrigation of a wide range using remote sensing data, has a special important value. Studies on soil moisture and irrigation information provide better understanding about the drought.In this paper, on the basis of active microwave remote sensing inversion data, soil moisture index(SWI) data in 1992-2002 and 2006-2013, combined with geostatistical analysis methods, the spatial and temporal variation of surface soil moisture in the NCP was analyzed. Relationship between SWI, measured soil moisture of farmland and precipitation within the same period were analyzed by using correlation analysis. Irrigation information in the main growing season of winter wheat was extracted by the method of spatial overlay analysis. The main results as follows:(1) Correlation between SWI and measured soil moisture of farmland was different in different soil depth. It was significant correlated between SWI and measured soil moisture in(0~10cm), the correlation decreased with the increase of soil depth. The annual average SWI of NCP was about 45%~50%; spatial distribution of surface soil moisture in NCP had heterogeneity, the soil water content was obviously different in different regions, and it decreased from north to south.(2) The CV of annual SWI in NCP presents the tendency of increasing from southeast to northwest, differences of soil water content in southeast regions in different years were small and it were opposite in northwest. The correlation between annual SWI and summer SWI was the most strong, which meant the variation of summer SWI affected the annual SWI the most. The CV of monthly SWI in southwest was larger than that in northeast, which indicated that the differences of SWI between different months in southwest was larger than that in northeast. The soil water content in spring was obviously different in different years, but the differences were smaller in summer and autumn.(3) The SWI increased obviously in most areas in 2013 compared to that in 1992, it only decreased a little in a small region.(4) Increasing of yearly precipitation led to the increasing of soil water in southeast to a large extent, but the effects turned out to be less in northeast. The SWI changes could reflect precipitation in some extent.(5) Most areas in NCP in 1999 were irrigated in different degrees in the main growing season of winter wheat; the irrigation times in the middle part was the least, and there existed two or three rounds of irrigation in the northern and southern part, which accounted approximately 65% of the total study area. The irrigation cells was 79.69% same with extracted result using land use data in 2000, and the study results and methods can provide references for the agricultural drought monitoring based on remote sensing. |
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