| Drought is a complex natural phenomena, and its formation and strength go through a long-asymptotic and cumulative process. Drought is one of the highest frequency meteorological disasters, with its long duration and large influence areas. It brings great losses to the agricultural production and human lives. China is one of the worst drought hazards and the most frequent in the world. Drought and even large drought occurred on average two or three years. It takes a great significance on the national economy, especially on the agricultural production. The water retention of soil has important implications for regional droughts. Agricultural drought is indexed by soil moisture and soil moisture. Soil moisture is an important index to reflect the areas of agricultural drought, and it is hard to obtain. Due to different types and nature of the soil, the soil water retention is different, different soil water retention for the prevention of Southwest drought has important significance.Based on the Meteorological drought and remote sensing monitoring, this paper, taking Southwest China as an example, used the method and technology of GIS, RS and Mathematical statistics and selected suitable calculation method of meteorological drought indices and vegetation index in the study area to analyze three typical response of vegetation index to drought and drought distribution characteristics in Southwest China. Based on the Meteorological drought and vegetation index in Southwest China the soil water retention index was deduced and its spatial distribution was researched.The main contents and conclusions were as follows:(1) Spatial and temporal distribution of three typical drought events in Southwest showed that, both interannual and seasonal variation, there was less rainfall in the high temperature areas, which may be one of the causes of drought. The drought mainly appeared in June-August in the summer of 2006, and drought mainly occurred in the eastern region of the southwest region, the eastern region of Chongqing and Yunnan-Guizhou Plateau more serious. A large area drought occurred in Southwest region in the winter of 2008, and severe drought appeared in Guangxi, southern of the Guizhou, and Yunnan-Guizhou Plateau. A drought occurred in the Southwest regions, with different degree in period of time from the autumn of 2009 to the spring of 2010 in which the most severe drought appeared in February, and eased in April,2010.(2) The response of vegetation index to drought events of Southwest region was analyzed. The precipitation anomaly percentage and NDVI lagged one month were strong correlated in spatial distribution in the summer of 2006 in which the drought occurred nearly half of the entire Southwest region. Two-thirds of the Southwest regional appeared drought in the winter of 2008, Vegetation index changed greatly, and no significant correlation between the precipitation anomaly percentage and the NDVI lagged one month. The southwest region appeared persistent drought in which 2/3 region appeared more serious drought than the others in period of time form the autumn of 2009 to the spring of 2010, and there were strong correlation in spatial distribution between the precipitation anomaly percentages and the NDVI lagged one month. From the study on relation between vegetation types and drought, it was induced that the grassland and the dry land were more sensitive to drought than the various types of woodland and lagged one month NDVI of the grassland and the dry land was strong related to the precipitation anomaly percentage. Relatively speaking, forestland was less affected by precipitation.(3) The soil water retention index (SW) was induced using the standardized precipitat-ion evapotranspiration index and vegetation condition index. In this paper, the precipitation data and vegetation condition index in the Southwest region of China in 2009 were used to induce soil water retention index and it was tested by measured data of soil relative humidity. Soil water retention index could better reflect the soil water capacity of Southwest region. The spatial distribution characteristics of soil water retention in Southwest China were analyzed. The soil water retention was better in midwest of sichuan、central and eastern regions of Yunnan、west and northwest of Guizhou and southwest of Guangxi. The soil water retention was poor in eastern and southwestern Sichuan、Chongqing、the northeastern of Guizhou、the northeastern of Guangxi and southwestern Yunnan. The soil water index, which was induced from meteorological drought index and remote sensing vegetation index, had provided a scientific basis for regional drought disaster monitoring and prevention. |
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