Research On The Impact Of Urban Land Expansion On Urban Floods And Its Correlation

With the rapid urbanization process in my country,the population is rapidly gathering in cities,and the scale of cities is expanding rapidly,changing the original land use type and forming an urban pattern that is different from the natural situation.Land use change,characterized by the increase of construction land and the reduction of green vegetation,has resulted in a multiplier of land use pressure.At the same time,the proportion of urban construction land is increasing day by day,which has changed the original process of production and confluence,resulting in frequent occurrence of urban waterlogging,which has a serious impact on social and economic development.Relying on the key project of the National Natural Science Foundation of China,"Research on the Theory and Method of Urban Waterlogging Disaster Prediction and Early Warning Based on Big Data"(No.51739009),this paper takes the main urban area of Zhengzhou,the core city of the Central Plains urban agglomeration and a typical city of rapid urbanization,as the research object,analyze the characteristics of urban land expansion from the perspective of urban expansion intensity and expansion direction,deeply excavate the impact of urban land expansion on urban waterlogging,and reveal the corresponding relationship between the two.The impact on rainwater regulation services can provide reference and guidance for the construction of sponge cities.The main work and achievements are as follows:(1)Analysis of urban expansion characteristics: based on the CART decision tree method to extract the land use situation in the study area;analyze the evolution process of land use types through the land use transition matrix;realize urban expansion intensity analysis based on urban expansion characteristic parameters;based on construction land standards The quadrant units divided by the difference ellipse and the same vertex sector are used to count the urban expansion increment,so as to realize the intuitive display and analysis of the evolution process of the urban expansion direction;the change of the landscape index is used to describe the change of the urban landscape pattern.The results show that the classification results of the CART decision tree are good,with an average accuracy of 90%.During the 25-year period,the land use changes in Zhengzhou City have been strong,mainly manifested in the transformation of cultivated land into construction land;Zhengzhou City expansion shows obvious periodic changes in time and space.,in 2005-2010,the urban expansion intensity is the highest;in terms of space,the urban expansion area is the highest in the southeast.(2)Analysis of the impact of land use change on urban waterlogging: Based on the SCS model,by simulating different rainfall scenarios and urban surface runoff at different urban development stages,the impact of land use change on runoff depth and runoff depth in different urbanization development stages was analyzed.Based on the land use data of 6 periods,the urban boundary is divided,the urban stormwater regulation service in different periods is analyzed,and the impact of urban land use change on the stormwater regulation service is quantitatively assessed.The results show that: the change of urban land use type leads to the increase of urban runoff under the same rainfall scenario,and the main runoff structure changes from cultivated land to construction land;the rainwater regulation service in Zhengzhou shows a trend of first increase and then decrease,which has an impact on the rainwater regulation service.The change from the greater impact of the new expansion area to the greater impact of the old urban area,at the same time,due to the difference in the direction of urban expansion,the changes in stormwater regulation services in each subcatchment area are different.(3)Research on the correlation between urban landscape pattern and urban waterlogging: Through the correlation analysis and multiple stepwise regression analysis of urban landscape pattern changes,simulated runoff and measured urban waterlogging points over the years,the correlation between each correlation index and urban waterlogging was explored.The results show that the indices with strong correlation with surface runoff depth are Shannon Diversity Index(SHDI),Contagion Index(CONTAG),Construction Land Patch Association(COHESION)and Patch Density(PD);The indices with the strongest correlation of point density are the average impermeability,the patch association index of construction land(COHESION),and the Shannon diversity index(SHDI).