Research On Risk Assessment And Spatio-Temporal Variation Of Flood Disaster In Nanning Area Based On GIS

In this paper, as Nanning aera of Guangxi for the research object, using a comprehensive evaluation method with the GIS spatial analysis function, from three aspects hazard factors, disaster environment, hazard bearing body, select annual precipitation, terrain index, the impact factors of river system, annual torrential rain days, the density of population, cultivated land ratio, industrial production per unit area, per unit area eight indexes such as value of agriculture, forestry and fishery production, building flood disaster evaluation system. With AHP method to determine the index weight, basing on the choice of flood disaster risk assessment model respectively in Nanning aera 2005-2012 conductes flood hazard, vulnerability and integrated risk assessment, and the flood disaster risk assessment results in the 2005-2009,2009-2012 and 2005-2012 period are analysed comparatively in time and space evolution.First of all, all kinds of evaluation of Nanning aera shows:the high risk area mainly concentrating in the Yongjiang river, ZuoYoujiang coastal and inland border on both sides, parts of Qingxiu and Xixiangtang area also has higher risk. In 2005-2012, the spatial distribution of flood disaster rating changes. The sum of high disaster and more high disaster area dropped from 33.72% in 2005 to 20.27% in 2012, they show a trend of decrease. Secondly, the flood risk levels shows:2009-2012 flood disaster comprehensive dynamic degree of risk the largest,2005-2009 and 2005-2012 are relatively small, suggesting that the overall risk level of the period change rate of less than a single time zone, and between each of the individual periods risk level change rate is also different. In addition, the flood risk index shows:flood risk changes vary widely, are at increased risk of parts and parts on the decrease. In 2005-2012 years, presents a whole increased flood disaster from the southwest, northwest to northeast trend, Qingxiu, Xingning northeast of increased disaster, Southwest parts increased disaster zone of Liangqing area, Xixiangtang Jiangnan for disaster reduction area as a whole. Finally, to all levels of risk dynamic structure analysis shows:between each risk level increasing, exchange between the risk level is active, the entire session commutativity is more than a single session. In 2005-2009 years, significant exchanges between the low and moderate disaster only; in 2009-2012 years, the significant exchanges between low-disaster and low disaster, low disaster and moderate disaster; in 2005-2012, significant exchanges between low-disaster and low disaster, medium disaster and low disaster, medium disaster and high disaster, medium disaster and high disaster significantly. Moderate disaster of connectivity rate is 0.75, number of connected to 3, shows that the disaster of stroke in the later evolution process, activity is the largest.Results from flood risk assessment shows that Nanning aera in high-risk flood areas are mainly concentrated in the Yongjiang both sides of the junction of the coast and the river, which is the focus area of flood control, governments and relevant departments should strengthen the awareness of flood control decision-making in these areas, make the appropriate flood mitigation work.