| The low elevation coastal zone(LECZ)in China is densely populated and economically developed.It is also prone to natural disasters.However,previous studies mainly focused on the risks and impacts of single disasters such as sea-level rise,typhoon,storm surge and flood under climate change,and lacked with a research gap on the multiple disasters.The low elevation coastal zone(LECZ)in China is densely populated and economically developed urban agglomerations in the Yangtze River Delta,the Pearl River Delta and the Bohai rim,as well as many large cities such as Shanghai,Tianjin,Shenzhen,Guangzhou and Ningbo.In this work,we analyzed the characteristics of population exposure changes in The low elevation coastal zone(LECZ)in China under different disasters from 1990 to 2015 based on high-resolution population data,new coastal DEM data,ground motion peak acceleration data,flood area-possible inundation range data,GTSR extreme water level data,tropical cyclone data,administrative division data,etc.Then we selected Seven indicators to build a multi disaster exposure assessment model to identify the cold and hot spots exposed to multiple disasters in LECZ from 1990 to 2015 and analyze their change characteristics.(1)Firstly,the range of the low elevation coastal zone(LECZ)in China is determined based on DEM data,and its area is counted.The results show that the low elevation coastal zone(LECZ)in China is about 213000 km2,accounting for 14.6%of the total area of China's first-class coastal administrative regions and 2.25%of China's total land area.(2)Based on the peak acceleration data of ground motions in China,the high-risk areas for earthquakes in the LECZ of China are determined and defined as HSHA.The HSHA in the LECZ in China is 151,000 km2,accounting for about 70.6%of the total area of LECZ in China.The population in the HSHA of LECZ in 2015 was approximated 168.69 million.with an increase of 60.2 million(39.2%)from 1990 to 2015,which mainly concentrated in the Yangtze River Delta,Pearl River Delta and Bohai Rim regions;Zone ? had the largest population increase of 54.27 million(61.41%),and ? zone had the largest population density in HSHA.(3)Based on the flood inundation map,the floodplain area of LECZ in China was determined.The floodplain of LECZ was 126,000 km2,accounting for about 58.9%of the LECZ in China.The results show that the population in the floodplain of LECZ was approximated 130 million in 2015,with an increase of 126.55 million(52.3%)from 1990 to 2015,which mainly concentrated in the Yangtze River Delta,Pearl River Delta and Central Bohai Sea area.The population showed an increasing trend at different inundation depths.The population with the 2-3m inundation depth increased the most,with an increase of 7.941 million(55.28%),and the population with the 7-8m inundation depth increased the most,with an increase of 84.11%(2.964 million).(4)Based on the GTSR extreme water level data to determine the possible inundation range of storm surge in LECZ,The possible inundation area of storm surgeextreme water level in LECZ was 148,700 km2,accounting for about 68.15% of the LECZ in China.The results show that in 2015,the population of the LECZ storm surge flood prone area was 183.24 million people,and from 1990 to 2015,the population of the LECZ storm surge flood prone area increased by 79.61 million people(76.8%),and the population density increased by 535 people/km2.(5)Based on the typhoon level data,areas that may be affected by typhoons was determined,and the cyclone intensities 1-2 and 3-5 were divided into two different levels,Ss1-2 and Ss3-5.The area is about 193,000 km2,accounting for about 90.2% of the LECZ.The results show that the population affected by the typhoon approximated 198.4 million people in LECZ in 2015,and the population affected by the typhoon increased by 65.71 million people(49.5%)from 1990 to 2015.Ss3-5 has the largest population,and the population of Ss3-5 increased by 90.81 million(83.7%)from 1990 to 2015.(6)Based on the ArcGIS classification statistics module,the exposed population and total population at the county scale of each disaster type in the LECZ of China,the exposed population and the proportion of the exposed population in the ? degree zone,? degree zone and ? degree zone of the earthquake disaster,the proportionthe of exposed population and the proporthe tion of exposed population in the floodplain,the prthe oportion of exposed population and the proportion of exposed population under storm surge-extreme water level,the proportion of exposed population and the proportion of exposed population in Ss1-2 and Ss3-5 were selected As model building indicators,the exposure indices at the county scale in the LECZ from 1990 to 2015 were derived through data transformation,identification of outliers and grading of exposure indices,and the distribution and changing characteristics of exposure classes and changes in exposure indices in the LECZ were analysed.The results are as follows.In terms of the distribution characteristics of exposure grades,the exposed counties in the coastal lowlands have the largest proportion of very high-grade and highgrade exposed counties,with very high-grade mainly concentrated in the urban agglomerations of the Yangtze River Delta,Pearl River Delta,Beijing-Tianjin-Hebei and Liaodong Bay,while very low-grade and low-grade counties are scattered,with Taiwan Province accounting for the largest proportion.Guangdong Province is the province with the largest number of exposed counties in the coastal lowlands,as well as the province with the largest increase in exposed counties of low grade and the largest decrease in very low grade;Jiangsu Province has the largest number of exposed counties of high grade and very high grade,while the number of all four grades increased from 1990 to 2015,except for the decrease in the number of very high grade;Shanghai has all very high grade;the number of exposed counties of low grade is smaller and mainly distributed in Guangdong Province,Zhejiang Province,and Shandong Province.In terms of changes in the number of exposed districts and counties by grade,from 1990 to 2015,the number of very low-grade districts and counties in the coastal lowlands increased by two,low-grade districts and counties decreased by three,medium-grade districts and counties increased by seven,high-grade districts and counties decreased by a total of two,and very high-grade districts and counties decreased by 10.From 1990 to 2015,the exposure index showed a trend of "increasing in the south and decreasing in the north".The exposure indices of Zhejiang Province,Shanghai,southern Jiangsu Province,Fujian Province,and Guangdong Province generally showed an increasing trend,while the exposure indices of areas north of Jiangsu Province generally showed a decreasing trend.In terms of the exposure indices of provinces and counties,in 2015,the exposure indices of Guangxi Zhuang Autonomous Region,Hainan Province,Hong Kong,Macao and Taiwan as a whole were on the low side,with the hi,ghest being Qionghai City in Hainan Province,with an exposure index of 4.3.Except for the above provinces,the highest exposure indices of the remaining provinces were all above 7,with the highest being Minhang District in Shanghai at 9.8;the lowest exposure indices ranged from 0.1 to 7.2,with an exposure index of There were 101 counties with an exposure index of 0.1,of which Taiwan Province accounted for the largest share.from 1990 to 2015,the exposure index in Nanshan District,Shenzhen City,Guangdong Province,increased the most,with 166.67%,while Dongying District,Shandong Province,increased the least,with 1.16%;Pingshan District,Shenzhen City,decreased the most,with 87.5%,and Putuo District,Shanghai City,decreased the least,with 1.04%.In 2015,the exposure indices of Shanghai,Jiangsu Province and Tianjin were generally high;Shanghai accounted for 50%of the top 20 districts and counties in the exposure index.Suzhou City accounted for 15%,Tianjin City for 20% and Nanjing City for 15%. |
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