Analysis Of Area Precipitation Thresholds Of Rainstorm-flood And Flood Risk In Guanting Basin

Global climate has been warming up persistently in the recent decades. Climate change may lead to the changes of climate extremes, including frequency, intensity, spatial scope and duration time and cause unprecedented extremes. According to the Fifth Assessment Report, some climate extremes has been changed due to the emissions of greenhouse gas. Droughts and floods are the most serious extreme disasters in China, with global wanning, the frequency and intensity of extreme droughts and floods will increase, and the effect will be further expanded. The early warming of storm flood disasters and risk assessment has great significance for disaster prevention and reduction, and for the sustainable development of social economy.This paper took the Guanting basin as the studied area, HBV hydrological model was applied to simulated the hydrological process of the basin, with the support of GIS. Then, established the relationship among area rainful, runoff, and water level. According to the water level of 10-year return period,30-year return period,50-year return period,100-year return period as critical criterions for different warning grades, which are calculated by the optimal distribution function, the area precipitation thresholds are determined. Based on the digital terrain, landuse data, and other data, established the two dimensional GIS raster based dynamic flood risk estimation model, and simulated the flooding process of the upper basin of guanting reservoir. The hydrograph data used in the simulation was calculated by the four level warning grades. The results are as follows:(1) The annual temperature in the Guanting basin shows a significant upward trend during 1061-2013. An abrupt warming occurred in about 1990. In the space, the distribution shows the higher temperature in the east part and lower temperature in the north and northwest part. The precipitation shows a downward trend, there is no obvious mutation. In the space, there is more precitation in the west and east part than in the central. Most of the meteorological stations in the region show the decline trend of precitation. During the period of 1956-2000, the runoff shows a downward trend, in addition, runoff catastrophe appeared in 1984-1985.(2) Taking 1971-1974 as the calibration period,1975-1978 as the validation period, HBV model is established. The results show that:HBV hydrological model is good in simulating the runoff of Guanting basin, the decisive coefficient between simulated value and measured value in calibration and validation periods are 0.68 and 0.67, the Nash-Suttcliffe value was 0.68 and 0.70.(3) The daily runoff during 1961-2013 is simulated by the estibalished HBV hydrological model. Based on the relationship among area rainful, runoff, and water level, the water level of 10-year return period,30-year return period,50-year return period,100-year return period is determined as critical criterions for different warning grades. On the basis of the hydrological model, the area precipitation thresholds are detennined, three strong precipitation processes are used to verify the efficiency, the results show that:the area precipitation thresholds of rainstorm-flood hazard determined by hydrological model are efficient in flood warning.(4) According to the digital terrain, landuse data, and other data, the two dimensional GIS raster based dynamic flood risk estimation model is estibalished and used to simulate the flood process of upper basin of guanting reservoir. The hydrographs input location is fixed in xiangshuibao hydrological station, the hydrograph data is the runoff produced by the four area precipitation thresholds. The results show that:the flood processes of the four input schemes are similar, but with the increase of flood volume, the flood evolutionary pick up.(5) During the simulation, the flood depth change rapidly. After 96h simulation, most flood depth of the least input volum is 0.5-2m, but the most input volum cause majority region with the flood depth of 4-6m.(6) The loss ratio index, the grain yield per unit area and the purchase price of Hebei Province during 2008-2012 are used to estimate the potential losses. The estimate argiculature losses of the four input schemes are:72.889million,92.228million,102.231million and 111.574million.