Abstract:

The research of flood disasters in history could provide analogies for better understanding the mechanism and impacts of the current and future floods.Today the research of historical flood is playing a more and more important role in the risk assessment and prediction.During the recent 300 years,there were lots of floods in China,especially in the southeast China,which can be given evidences by lots of historical documents before the instrumental meteorological observation.It can help to make sure the advantage of doing research on historical floods in China.This paper selected Jiangsu,Zhejiang,Shanghai provinces as the study area and constructed the historical floods database from 1644 to 1949AD according to historical document.The historical extreme flood years were identified according to the statistic analysis of annual floods counties.Then the paper analyzed the exposure of population and GDP of this area in 2010 under the scenarios of these historical extreme floods years without caring about the changes of the characters of hazardaffected bodies and margin of exposure.Results are as follow.(1) The worsthit year in recent 300 years in JiangsuZhejiangShanghai area was 1931AD,and the frequency of this flood was once in 300 years,which involved about eightysix counties.The worsehit years were 1823 and 1849AD and their frequency were between once in 100 years and once in 300 years,which involved about eighty counties.In 1670,1683,1804AD,the frequency were between once in 50 years and once in 100 years,which involved about sixty to seventy counties.(2) The paper recovered the spatial distribution of these historical extreme floods through the GIS tool and statistics.It is found that disastrous areas were mainly distributed in the Yangtze River Delta Area,including shanghai,the southern Jiangsu and northern Zhejiang.(3) It calculated the exposure of GDP and population in JiangsuZhejiangShanghai area in 2010 under the scenario of these extreme floods,it is found that if these extreme floods happened in 2010,JiangsuZhejiangShanghai area was relatively vulnerable and suffered great losses.The percentage of GDP and population's exposure almost accounted for more than 40% of the total,especially GDP exposure had risen to 50% of the total GDP.(4) The extreme floods had different impacts in different disastrous areas.Jiangsu was relatively suffering more than others.The fluctuation of disasters impacts in Shanghai was bigger than that in Jiangsu and Zhejiang,especially when the frequency were between once in 100 years and 300 year;the exposure was obviously larger than those years that the frequency were between once in 50 years and 100 years.Shanghai should be more vulnerable and cautious about the extreme floods with frequency of once in more than 100 years.Zhejiang exposure in these extreme floods scenarios was relatively little fluctuant.Zhejiang was less sensitive to the flood than Jiangsu and Shanghai.(5) There was no significant correlation between the exposure of the population and GDP and the number of disastrous counties.Higher exposure doesn't mean larger disastrous spatial distribution,because of the economic and population's unbalanced growth