Hazard assessment of urban flood disaster and safety protection strategy for flood disaster prevention and reduction in China

Based on disaster system theory and analysis of 70 cities in China whose population is over 600 thousand, a hazard assessment system has been established combining hazard-formative environments, hazard-formative factors and hazard-affected bodies of these cities. The integrated hazard index has been put forward by means of analyzing the cause of urban flood disaster formation, and the corresponding map has been set up. The result shows that: these cities are bearing flood risk to different extent; the flood risk is highest in Tianjin, Wuhan and Guangzhou, with the hazard index over 4.5; the risk of 12 cities in the study is severe with the hazard index between 3.5similar to4.5, which are in the core areas of Metropolitan regions; the risk of 18 ones is strong with the value between 3similar to3.5, but most of them are in the middle and lower reaches of Yangtze River and located in the areas with high-frequency of flood; about 17 ones have moderate values which are between 2.5similar to3; 16 cities have relative slight risk of value 2similar to2.5; The last four cities have the lowest hazard index which is less than 2. Based on the analysis of urban flood, security protection strategy for flood alleviation is put forward as the mode: "co-existing with flood", which combines defending, accommodating, and managing measurements together. This paper suggests that flood alleviation strategy should base on the combination of hazard-formative environments and hazard-affected bodies, and appropriate pattern of "flood occupied land" should combine with the type of urban flood hazard-formative environment of certain city, which comes from the foregoing idea.