Spatio-Temporal Changes Of Rainstorm And Flood Disaster Risk In China

Flood disaster is the most common natural disaster,easy to cause serious economic losses and huge casualties.China is a vast country with frequent flood disasters.About two thirds of China’s land area is threatened by flood disasters.With the increase of global greenhouse gas emissions,the global warming trend continues to intensify,resulting in frequent extreme precipitation events,which may increase the risk of flood disaster.Therefore,the analysis of the change trend of extreme rainfall events,the assessment of historical and future flood disaster risks and the identification of high-risk areas in China can provide scientific basis for flood mitigation and risk management in China,and promote the rational utilization of water resources and the healthy,stable and sustainable development of society.In this study,China was taken as the research area.According to the daily precipitation data of meteorological stations in China,the maximum annual 1-day precipitation(RX1),the maximum annual 5-day continuous precipitation(RX5),the number of annual rainstorm days(R50)and other extreme precipitation indexes were calculated during 1960-2020.The trend of extreme precipitation was analyzed by Mann-Kendall trend test and Sen’s slope.A flood risk assessment model was constructed using terrain,vegetation cover,river network,socio-economic,land use and meteorological data to evaluate flood risk in different recurrence periods(5-year,20-year,50-year,100-year)in China from 2000 to 2020.Based on the data of land use,river network density and elevation in 2020,overlay the daily rainfall data from 2020-2050 of CMIP6 and the socio-economic data in 2050,the flood risk of different recurrence periods in China in 2050 is assessed to identify the change of flood risk in the future.The main research results of this paper are as follows:(1)From the perspective of time variation of extreme precipitation events,the overall trend of extreme precipitation events in China was on the rise during 1960-2020,in which RX1 showed a significant rise trend,with a growth rate of 0.76mm/10a(p<0.05).RX5 showed an insignificant upward trend,with a growth rate of 0.43mm/10 a.R50 showed a significant increasing trend with a growth rate of 0.005d/10a(p<0.05).From the perspective of spatial variation,the variation trend of RX1 in China is that it increases in the west and southeast,and decreases in the north.RX5 increased in the southeast and northwest,but decreased in the middle.R50 increased in the southeast and south,and decreased in the middle of the east.(2)From the perspective of time variation of flood risk,the overall flood risk in China shows an increasing trend from 2000 to 2020.In particular,the high-risk area increased significantly,with the proportion of high-risk area of 5-year flood disaster increased from4.36% to 5.28%.The proportion of area with high risk of flood disaster once in 20 years increased from 9.04% to 10.89%;The area at high risk of 50-year flood disaster increased from 13.40% to 15.44%;The area at high risk of 100-year flood disaster increased from16.72% to 18.41%.From the perspective of spatial change,the flood disaster risk of different recurrence periods in China presents an overall increasing trend from northwest to southeast.Coastal cities such as Guangxi,Guangdong,Shanghai,Jiangsu and central cities such as Hubei and Henan are of higher risk or above,while most areas of Xinjiang,Shaanxi,Yunnan and Tibet are of lower risk.(3)From the perspective of time change of flood risk in the future,the overall flood risk in China shows an increasing trend from 2020 to 2050.The proportion of high-risk flood disaster area increased,while the proportion of low-risk flood disaster area decreased.The proportion of area with high risk of flood disaster once in 5 years increased from 5.28% to5.79%;The proportion of high-risk area of flood disaster once in 20 years increased from10.89% to 16.48%;The proportion of high-risk area of 50-year flood disaster increased from15.44% to 20.30%;The area at high risk of 100-year flood disaster increased from 18.41% to22.29%.From the perspective of spatial change,the overall risk of flood disaster in different recurrence periods in China in 2050 is decreasing from southeast to northwest.The coastal cities of Jiangsu,Shanghai,Zhejiang,Fujian,Guangdong and other coastal cities belong to the grade of high risk or above of flood disaster,while the risk of flood disaster in the northern provinces of Xinjiang,Qinghai and Inner Mongolia is low.(4)Climate change,land use,NDVI and socio-economic development are the key factors to determine the degree of flood risk in China,which should be fully considered in disaster prevention and reduction planning.