Analysis On The Evolution Of Drought And Flood Disasters In Guangxi And Their Social Impacts In The Last Millennium

Since ancient times,droughts and floods have caused great harm to social economy and people's lives.In ancient times,droughts and floods caused food cuts and famines,and even "human-eating" tragedies that violated ethics.In the modern,droughts and floods may even cause economic losses of tens of millions of yuan.From history,we can see the changing laws of hydrology and climate and the course of social development.Studying historical droughts and floods will help us improve the current management level and predict the future,and also help achieve the ambitious goal of Guangxi's sustainable development.Our country has a long history and many ancient books.It has made many achievements in the study of historical droughts and floods.However,more mature studies are concentrated in the northwest,north and east regions,and Guangxi has relatively few research records.This study is based on the historical records of flood and drought disasters in Guangxi City and County(AD 960-1994),"Yearly charts of dryness/wetness in China for the last 500-year period" and two supplements(AD 1470-2000),and the statistical tables of the floods in 1950-2017 and the statistical tables of the affected population and economic losses in 2011-2018 in various cities in Guangxi,etc.,mainly using historical literature collection methods,mathematical statistics methods,spatial statistical analysis methods,and taking Guangxi as a study Area,to analyze the evolution of drought and flood disasters in Guangxi in the past millennium and their social impacts.The main research contents and results of this paper are as follows:(1)Reconstruct the sequence of drought and flood disasters in Guangxi in the last millenniumDivide the drought and flood disaster into 5 grades,and use the "1st,2nd,3rd,4th,and 5th grades" to correspond to the "waterlogging,partial flooding,normal,partial drought,and drought" disasters in the text description,and then rebuild the millennium According to the drought and flood disaster rank series,it is found that the Guangxi area is dominated by light disasters.For light disasters,there are more water disasters than drought disasters,but severe disasters occur occasionally,and for severe disasters,there are more drought disasters than waterlogging disasters.Over time,droughts and floods have become more frequent.(2)Analysis of the distribution characteristics of drought and flood disasters in GuangxiThere were few disasters during the Southern and Northern Song Dynasties,with more flood than drought in the Northern Song Dynasty and more drought than flood in the Southern Song Dynasty.After the Yuan Dynasty,disasters gradually increased,and the drought and flood situation changed from drought to flooding in 1310 AD.The droughts and floods in the Ming Dynasty were relatively balanced.The climate was warm and disasters were less in the early Ming period.The climate became colder after the Ming and Qing glacial periods in the later Ming period.Disasters increased rapidly,and extreme floods or droughts often occurred.The frequency of droughts and floods in the Qing dynasty was the highest among all dynasties,and the conversion time of droughts and floods was short,and there was no obvious phase.However,disasters increased sharply after 1850.Over the years,the floods were more than the droughts.During the Republic of China,disasters were more frequent,and flooding was more common.Large-scale extreme flooding occurred in the early stage,while droughts occurred in the middle and late stages.After 1935,the proportion of drought and flooding gradually became balanced.During the period of New China,the disaster incidence rate reached its peak,and the disaster area and disaster losses were the highest in history.To sum up,it can be found that the trend of each dynasty is consistent with the general trend,that is,more and more disasters are more frequent,on the one hand,it is because the disaster is indeed more frequent,on the other hand,it is because the number of records in modern times is more abundant.(3)Analysis of the annual distribution characteristics of drought and flood disasters in GuangxiAccording to the seasons,the droughts and floods in Guangxi are about equal in spring,with more floods in summer and more droughts in autumn,and fewer droughts and floods in winter.From a single-season perspective,summer floods are the most frequent and winter floods are the least.From a multi-season perspective,it is mainly due to more frequent disasters in the two seasons,and even more drought than flood.Continuous drought occurs most frequently in springsummer and summer-autumn,followed by autumn-winter and winter-spring.From a geographical perspective,the distribution of droughts and floods is roughly the same as the rainfall distribution and the advancing direction of the flood season.(4)Analysis of the spatial distribution characteristics of drought and flood disasters in GuangxiFlood is common in northeast and southeast,drought often occurs in southeast,central,and northeast,and there is a separate high value area of drought in Chongzuo.The cause of the severe disaster may be due to the lack of precipitation,and the cause of the mild disaster may be related to the conditions of the underlying surface.In addition,regions with high incidence of floods in various dynasties always gather nearby.The occurrence area of clusters of floods moves from the northeast to the east,while the drought only shows a significant positive correlation in the Yuan and Qing dynasties.Moving towards the middle,there is no obvious clustering in other dynasties.The spatial pattern of population in the history of Guangxi has a certain similarity with the spatial pattern of drought and flood.(5)Impact of drought and flood on Guangxi societyThe droughts and floods mainly caused losses to agricultural production,population,riots and the economy.The study found that the area of farmland affected by flood between 1950 and 2017 is currently in a relatively rising stage of large-scale fluctuations.A large number of deaths due to disasters occurred mainly in backward ancient times.After 1750 AD,the population began to explode,and disasters could no longer affect the growth momentum.The impact on social stability is mainly reflected in the riots triggered by the people's desperation.The riots broke out across Guangxi during the Qing Dynasty.In terms of economic loss,the economic loss caused by disasters increased year by year from 2011 to 2018,but the growth rate of economic losses caused by disasters is always lower than the growth rate of GDP.(6)Put forward corresponding management countermeasuresThe drought and flood in Guangxi can be summarized as climate type,landform type,hydrological type,and man-made type according to the causes.The corresponding management countermeasures are: strengthen embankments,build reservoirs,strengthen urban drainage systems,dredge natural drainage systems in karst areas,plant special drought-resistant and floodresistant crops,build water conservation areas,disaster risk zoning,and establish disaster monitoring systems using "3S" technology.