Study On Risk Assessment Of Sand Storm Disaster Based On RS And GIS

Based on the regional disaster theory, this paper used RS and GIS technology to analyze the characteristics of sandstorm disaster and screen indexes about disastrous factors, disaster-pregnant environment and disaster-body. Finally, it established relevant index system according to sandstorm disaster evaluation model established by ahp and fuzzy comprehensive evaluation, so as to analyze integrated risk for sandstorm disaster in Xilin Gol League during three periods, from 1981 to 1990,from 1991 to 2000 and from 2001 to 2010. The conclusions are as follows:(1) Sandstorms occurring in spring account for 77.7% of all year and have obvious seasonal characteristics. Every year sandstorm always occurs in March, April and May, especially in April the frequency is the highest (account for 40.74%). But it becomes less after June. From 1971 to 2000, sandstorm has a descending trend. After 2001, it occurs more and more. The general trend of spatial distribution gradually decline from west to east. Meanwhile, the center of sandstorm-common area is located in the west (Sonid Right Banner and Zhurihe). However, the annual change waves of each banner are obviously different and the west is more changeable than the east.(2) It got the class division map of risk about disastrous factors of sandstorm in Xilin Gol League during the three periods (1981-1990,1991-2000,2001-2010) by fuzzy comprehensive evaluation. Generally, the risk in the first and third period is higher than the one in the second period. And it shows high-low-high trend in time series. As relative spatial, the north and east (Wulagai, Dongwuzhumuqin Banner and Xiwuzhumuqin Banner) are in low and lower grade risk area; the middle (Abaga Banner and Xilinhante) are in lower grade risk area; the west (Sonid Left Banner, Sonid Right Banner and Zhurihe) and five banners in the South (Xianghuangqi, Zhengxiangbaiqi, Zhenglanqi, Duolun and Taipusi) are changing in lower, moderate and higher grade risk area. The risk in these banners in the same period is higher than other banners.(3) For the evaluation of risk about sandstorm disaster-pregnant environment, it has two types, meteorological environment and underlying surface environment, according to layering process.For the meteorological environment indexes, factors having higher correlation with days with sandstorm are elected on the basis of wind velocity, days with threshold sand, air temperature, and rainfall and ground temperature provided by weather stations. Also, risk index about sandstorm meteorological disaster-pregnant environment are established by using the largest variance to find out three comprehensive factors (dynamic factor, moist factor and thermodynamic factor). For the underlying surface environment indexes, based on the formation mechanism of sandstorm and combined with the former studies, three layers'index system are constructed through five aspects source regions, land use, soil erodibility, vegetation coverage and snow index.The conclusion of analyzing the risk about disaster-pregnant environment in Xilin Gol League is that the risk grade of Xilin Gol League is in low, moderate and higher levels. During the first period the percentages are separately 42.64%,23.46% and 18.29%; the second period are 45.50%,21.57% and 17.76%; the third one are 39.11%,35.25% and 19.11%. The area with highest grade risk about sandstorm meteorological disaster-pregnant environment are in the west(Sonid Right Banner and Zhurihe), and the area in the three periods account for 2.02%,0.36% and 0.51%.It can be concluded from the heterogeneity of temporal and spatial distribution of risk about disaster-pregnant environment that:the change of, snow index and land use is the main reason of high-low-high trend of risk about disaster-pre vegetation coverage gnant environment during the three periods. The climatic factor (dynamic factor, moist factor and thermodynamic factor) and soil erodibility are the direct reason of the general trend of spatial distribution gradually declining from west to east. Meanwhile, the seasonal change of vegetation coverage and snow index are the major reason of seasonal change about disaster-pregnant environment.(4)For the vulnerability index of sand storm hazard-bearing body, agriculture, forestry, husbandry, industry, communication, transportation,people's life, property, and health are took into consideration. Finally, the indexes involve in population density, farmland percentage, heavy livestock proportion, grazing capacity, traffic lines density, total output value proportion of three major industries, number of medical technique people, and numbers of million people beds.The conclusion is that:during the three periods, the vulnerability of hazard-body in Xilin Gol League shows a descending trend, especially in the five banners of the south and Xilinhaote of the middle and Dongwuzhumuqin of the east. The population increase slowly and the number of livestock penned and overload rate get controlled. Also the net income of herdsmen is rising annually (especially after 2000). Urbanization process develops reasonably. The industrial structure is based on the primary industry and assistant secondary and tertiary industries. Proportion of three major industries (except Erlianhaote)is nearly 3:4:3. Industrial structure which was based on agricultural and animal becomes rationalization and diversification. This change depends on the development of society and wind and sand storm control project and returning farmland to forest carried out in Xilin Gol League, which made production and management mode, life style, industrial structure, per capita income, structure of income source change essentially. Also the two projects have effect on reducing the vulnerability of sand storm hazard-bearing body.(5) Based on the analysis of risk about disastrous factors, disastrous-pregnant environment and vulnerability of hazard-body, the risk assessment system of sandstorm are constructed. After that, the map of risk assessment of sandstorm in Xilin Gol League through risk grade division matrix. Generally, Xilin Gol League during three periods is in moderate and lower grade risk area. In the first and third periods the mid-eastern Xilin Gol League (Xilinhaote, Dongwuzhumuqinqi and Xiwuzhumuqinqi) and Erlianhaote in the west are in lower grade risk area, and the other banners are in moderate one. During the second period, the risk in Dongwuzhumuqinqi chang from the lower to the low and the risk in Abagaqi change from the moderate to the lower.