Risk Assessment And Regionalization Of Drought Disaster In Chongqing

Drought has long duration,wide distribution and great influence,which often seriously restricts regional social and economic development and destroys regional ecological balance.Carrying out drought disaster risk assessment in Chongqing from the aspects of disaster environment,disaster-causing factors,disaster-bearing bodies,disaster prevention and mitigation capabilities,etc.,can provide reference opinions for drought disaster risk management,assist relevant departments in disaster prevention and mitigation,and effectively promote regional healthy and stable development.Based on the grid precipitation data from 1917 to 2017,this thesis uses fractal dimension,standardized precipitation index and drought evaluation index to analyze the spatial and temporal characteristics of drought in Chongqing.17 specific indicators were selected from four dimensions: disaster-bearing environment,disaster-causing factors,vulnerability to disasters and disaster prevention and mitigation capacity,determine the weight values of four dimensions by analytic hierarchy process,calculate the weights of 17 specific indexes by entropy weight method,and the index system of drought disaster risk assessment in Chongqing was established.Based on the theory of natural disaster system risk,the evaluation index system of drought disaster risk in Chongqing was constructed by referring to the frequency of evaluation indexes adopted by related research results at home and abroad,the corresponding data of 2010 and 2020 were obtained by GIS technology,and the comprehensive index method,TOPSIS evaluation method and SOFM network model method were used to comprehensively evaluate the drought disaster risk in Chongqing and classify the types,the main results are as follows:(1)Analysis of Dynamic Characteristics of Precipitation at Different Time Scales in Chongqing by Using 101-year Precipitation Data.The annual precipitation in Chongqing is generally rich,from 1917 to 2017,the average annual precipitation of 45 grid points was 952.00～1469.00 mm,and the average precipitation was 1220.00 mm,and the precipitation decreases gradually from the southeast to the west and north.There is a big spatial difference in seasonal precipitation,and the regional difference is obvious,the average precipitation in spring,summer,autumn and winter is 324.53 mm,514.73 mm,318.77 mm and 62.31 mm respectively.the results show that the fractal dimension value of annual precipitation in Chongqing has little change,generally ranging from 1.0023 to 1.0046,it shows that the precipitation process has little change from 1917 to 2017,but the spatial difference is obvious,the fractal dimension value is decreasing from northeast to southwest.(2)Analysis of Drought Characteristics at Different Time Scales in Chongqing Based on Standardized Precipitation Index.The frequency of total drought(light drought and above)in Chongqing is relatively high,with an average frequency of 30.71%,The spatial distribution is generally high in the northeast,and decreases to the southwest and southeast in sequence,and slightly increases in some districts and counties in western Chongqing;The drought occurred in a wide range,drought occurred in 89 years in 101 years,and81.00% of them were global drought;The annual drought intensity fluctuates from0.54 to 1.66,and it is generally classified as mild drought and moderate drought,with extreme drought occurring in autumn and winter,spatial difference of drought intensity is obvious.(3)The comprehensive index method and TOPSIS evaluation method are used to obtain the spatial and temporal characteristics of comprehensive risks in Chongqing,according to SOFM network model method,the comprehensive risk zoning of Chongqing is calculated.(1)The comprehensive risk index values of drought disasters in Chongqing in2010 and 2020 were between 0.3957～0.5324 and 0.3965～0.4807,respectively,and the overall risk index declined slightly;It is generally characterized by large dispersion and small aggregation in space,as time goes by,the value of comprehensive risk index keeps stable or slightly decreases in other districts and counties except northeast Chongqing;The comprehensive risk proximity values of drought disasters in each county are between 0.3287～0.5377 and 0.3169～0.5588 in 2010 and 2020 respectively,it shows an increasing trend from the west to the northeast and southeast of Chongqing respectively.(2)Based on Matlab software platform,the SOFM network model structure is established by using newsom function,thus,comprehensive risk of drought in Chongqing is divided into six types: Ⅰ～Ⅵ,the results show that the drought disaster risk in the study area has the characteristics of large aggregation and small dispersion,risk types Ⅰ and Ⅵ are the main ones,and there are 8 districts and counties that are type Ⅰ,mainly concentrated in the central city;There are 11 districts and counties of Ⅵ type,which are concentrated in northeast and southeast of Chongqing.