Quantifying The Relationship Between Ecosystem And Flash Flood Disaster And Estimating The Value Of Ecosystem Service For Flash Flood Disaster Reduction In Gan River Upsteam

China was one of the most flash floods-prone countries in the world. Frequent flash floods have caused huge casualties and property losses. Ecosystem owned important disaster prevention and reduction functions. But the quantitative relationships between ecosystems and flash floods and the value of ecosystem services for disaster reduction were still lack of in-depth study. This study selected the flash floods-prone Gan river upstream region as a study area, employed the retrospective cohort study of public health method and the small watersheds with flash floods were used as the basic units of the cohort study. This study investigated the spatial and temporal distribution of flash floods in small watersheds, and analyzed the dynamic changes of ecosystem based on remote sensing images. A relational model of flash floods indices and impact factors would be constructed, quantified the relationships of ecological characteristics with flash floods in small watersheds, analyzed suitable ecological restoration governance models for disaster risk reduction, and estimated the value of ecosystem service for flash flood disaster reduction in Gan river upstream region of China. The main conclusions were as follows:1) Natural ecosystems could mitigation the disasters. As the proportion of ecological land changed from the lowest level (0-20%) to the high level (60-80%), the frequency of flash flood disaster reduced by 50%.2) The disaster mitigation ability of different ecosystem types were different and the ability was in the sequence of the forest> wetlands> grassland> shrub. The disaster mitigation ability of different forest types were different and the ability was in the sequence of the broadleaf forest> coniferous forest> coniferous and broadleaved mixed forest. The disaster mitigation ability of different forest age were different and the ability was in the sequence of the near-mature forest> middle-aged forest, young forest.3) Disaster frequency was significantly associated with regional human activities, and human construction activity increases the risk of flash flood disaster, especially town construction and farmland.4) The risk of ecological condition of ecosystems to achieve the best scenario is about 0.606 times of the national average ecological status. Mitigation ecosystem services Situation value systems of 6.095 billion yuan, accounting for 3.31% GDP. The mitigation of ecological service value per unit land area of 1991.97 yuan/ha · years.5) In the study area by ecological construction with a total investment cost of 3.734 billion yuan, Disastrous formed 23.90 billion per year. By ecological construction in the study area can reduce the risk of flash flood disaster, compared to current situation in the study area can reduce the risk of 18.6%, compared to the national average of 31.4% can reduce the risk. Disasters caused by torrential flash floods fatalities 1.5 people, the threat of population decline year 2200, reduce the destruction of houses 54400, less direct loss of 87.1427 million yuan, reducing infrastructure losses 8.4619 million yuan,676,400 yuan to reduce other losses.