Spatial And Temporal Variation Characteristics Of Meteorological And Hydrological Disasters In Shanghai From 1978 To 2020

The analysis of spatial and temporal variation characteristics of past disasters is an important reference for disaster loss statistics,understanding of disaster change patterns,risk modeling and disaster mitigation and prevention.Shanghai is located at the eastern edge of the Yangtze River Delta.Meteorological and hydrological disasters have accounted for the highest proportion of natural disasters over the past four decades,with floods,typhoons,wind and hail as the main types of disasters.This paper collects and organizes data on floods,typhoons,and wind and hailstorms in Shanghai from 1978 to 2020,as well as socioeconomic data and information on the history of Shanghai's administrative divisions,based on data sources such as literature and codices.In this paper,we firstly analyze in detail the changes of pairs of administrative divisions that affect the statistics of disasters,and then,we analyze the damage of meteorological and hydrological disaster and the spatial and temporal variation characteristics of disaster frequency in Shanghai in the past 43 years by applying mathematical and statistical methods,such as MK trend analysis and three different mutation tests,and analyze the disaster intensity index of each district in Shanghai by developing the disaster intensity model.The main work and conclusions are as follows.(1)The types of administrative division changes are summarized,and the administrative division adjustments in Shanghai in the past 43 years are described in detail: Shanghai experienced 63 establishment changes from 1978 to 2020,and the change patterns are of the types of abolishing counties to build districts,abolishing Xiang to build towns,abolishing Xiang to build sub-districts,and building new administrative districts.They occurred in 1980,1981,1988,1992,1995,1997,1998,1999,2000,2001,2005,2009 and 2011.There were 9 times of abolishing counties into districts,including two changes of establishment in 1992,abolishing Shanghai County and old Minhang District to establish the new Minhang District in September and establishing Pudong New District in October.The change of Xiang to township occurred 4 times,the abolition of township to set up sub-districts occurred 15 times,and the construction and abolition occurred 35 times.The changes in scope are mainly reflected in the merging and splitting of sub-districts in each district,with a total of194 changes from 1978 to 2020.In addition,there are other types of administrative division changes,such as name changes and resident relocation.The major impact on disaster data statistics is the change of establishment and the change of administrative boundaries.(2)Summary and analysis of the temporal characteristics of the number of meteorological and hydrological disasters such as typhoons,floods and hailstorms in Shanghai from 1978 to 2020.The total number of disasters in the city shows a trend of oscillating upward and then downward,reaching a maximum of 14 times in 2008.Pearson,Spearman and Kendall correlation coefficients show that the number of typhoon disasters has negative correlation with the number of flood,and that of hailstorms to some extents;the occurrence of flood and hail disasters shows a certain degree of positive correlation.The MK test and the Theil-Sen Median indicate that there is an increasing trend in the annual frequency of typhoon disasters and a decreasing trend in the annual frequency of wind and hail disasters.Combining MK mutation test,Pettitt mutation test and sliding t-test,it shows that there is no significant mutation year in the annual occurrence of typhoon and flood disaster,while the annual occurrence of wind and hail disaster has mutated around 2010.The absolute values of the three indicators show the characteristic of "Biceps bulging in the middle,flat on both sides of the tail",and the extreme values appear in1991 and 2005.The historical evidences support that in 1991,the Jianghuai and Taihu Lake regions were subjected to continuous flooding of a "100-year event",and in2005,they were continuously affected by strong typhoons Matsa and Khanun within a short period of time.The relative indicators of the proportion of crop area affected,the proportion of population affected,and the proportion of direct economic damage that are calculated by introducing annual sown area,resident population,and GDP,show that the damage in 1991 was more severe than that in 2005.The chronological changes in the degree of damage caused by typhoons,floods and wind and hail hazards generally show an increase in 1991-2000 and 2001-2010 compared to 1978-1990,and a decrease in 2011-2020.(4)Summary and analysis of the spatial and temporal characteristics of the number of meteorological and hydrological disasters such as typhoons,floods and hailstorms in the 16 districts from 1978 to 2020.The frequency distribution of disasters in each district has its own characteristics.In general,the number of disasters shows the characteristic of "less in urban areas and more in distant suburbs",among which the total number of disasters in Huangpu District is the least,the number of typhoons in Jinshan District is the most,the number of floods in Minhang District is the most,and the number of wind and hail disasters in Songjiang District is the most.The regional disaster evaluation model optimally developed in this paper does not require complete data of all aspects of disaster indicators compared with traditional comprehensive disaster evaluation models,so it circumvents the limitation that some historical data are not exhaustive and standardized.The model mainly calculates the disaster index and disaster type index from two dimensions,namely,the degree of multiplicity of disasters and that of clustering of disasters,and then the disaster intensity index of each adminstrative district is obtained by weighting the cumulative trend year by year.The model shows that the historical disaster intensity of Jinshan,Minhang,Hongkou and Songjiang districts is more serious,with total disaster intensity of 80.4018,57.3871,56.2477 and 50.9478 respectively,accounting for 13.75%,9.82%,9.62% and 8.72% of the total disaster intensity in the city,which should be focused on when disaster prevention and measure taking.