Variation Characteristics Of Rainfall And Flood Risk In Pearl River Delta During Urbanization

Under the background of global climate change and rapid development of urbanization,extreme weather events occur frequently,and the problem of flood disasters in highly urbanization areas is becoming increasingly prominent.Frequent human activities have an important impact on the regional water vapor cycle,and the high concentration of population and wealth makes the vulnerability of the disaster bearing body increasingly prominent.It is of great scientific value and practical significance to further study the impact of urbanization development on rainfall and the change of flood disaster risk.Taking the Pearl River Delta region with rapid urbanization and high concentration of economic factors as the study area,this paper combs the development process and characteristics of regional urbanization,analyzes the temporal and spatial variation characteristics of rainfall structure and extreme rainfall events and their relationship with urbanization development,and conducts flood risk assessment research aiming at the changes of disaster-causing factors and disaster-bearing bodies before and after urbanization.The main conclusions of this dissertation are extracted as follows:(1)The main types of land use in the Pearl River Delta region are woodland and cultivated land.From 1980 to 2015,the area of construction land showed a sharp growth trend,with a growth rate of 152.05%,and its growth mainly came from the transformation of cultivated land and woodland.2000-2005 and 1990-1995 were the rapid growth periods of construction land,with the growth rates of 45.78% and 32.68% respectively.There are obvious differences in the degree of urbanization development among cities in the Pearl River Delta.Before 1990,it was a single-core pattern with Guangzhou as the center.After 2000,it gradually formed a pattern with Guangzhou-Shenzhen as the core,and together with Foshan,Dongguan,Zhongshan and Zhuhai,it formed a highly urbanized urban agglomeration.(2)From the perspective of rainfall duration,rainfall events are mainly short duration rainfall within 6 hours,but the main contributor of rainfall is long duration rainfall above 6hours,and the rainfall structure has not changed significantly.From the point of view of rainfall grade,rainfall events are mainly weak rainfall,but the main contribution of rainfall depends on heavy rainfall events which occur less frequently.Significant changes have taken place in rainfall structure,with a significant increase in the incidence of moderate and heavy rain and a significant decrease in the incidence of light rain.The change of rainfall structure in highly urbanized areas is the most obvious,with the incidence of moderate,heavy and heavy rain increasing significantly and the incidence of light rain decreasing significantly.(3)The extreme rainfall and extreme rainfall frequency in highly urbanized areas showed a significant upward trend,rising by 44.3mm/10 a and 1.6 times/10 a.The sudden change time was in the late 1990 s,which coincided with the rapid growth time of urban land in this area,but there was no obvious change in other neighboring areas.The significant increase of extreme rainfall in pre-flood season in highly urbanized areas is the main reason for the increase of annual extreme rainfall.In the Pearl River Delta region,the rainstorm type is mainly single peak type,among which type I rainstorm with the rain peak in front accounts for the highest proportion,which is about 33.7%,and the frequency of type I rainstorm in highly urbanized areas increases obviously.(4)Based on the risk-vulnerability assessment framework and index system method,the flood disaster risk analysis is carried out,and the map is drawn and analyzed Comparative analysis of flood risk zoning map before and after urbanization.The regionalization results show that the flood risk hierarchy in Pearl River Delta region has changed after urbanization,and the proportion of low-risk areas has decreased significantly,while the proportion of higher risk areas and high-risk areas has increased significantly,which is mainly due to the increase of higher risk areas and high-risk areas in highly urbanized areas.