| In recent years,extensive urban development has rapidly changed the land use pattern,and the encroachment of construction land on natural ecological space makes the permeable ground drop sharply,weakens the infiltration and storage capacity of urban surface for rainwater,and increases the risk of urban rain flood damage.In the face of extreme rainstorm weather caused by climate warming,the large area of impervious surface accelerates the collection of surface runoff,and further increases the intensity and effect of urban rainstorm flood,which seriously threatens the safety of people’s life and property.Urban green space,as the main natural ecological element in the built-up area,has obvious water storage and permeability.However,the low integration degree between urban green space network and river system network is low,which can not effectively play the functions of flood discharge and drainage,water storage regulation,and the ability to resist urban flood disaster.Therefore,through the analysis of the relationship between land landscape pattern and surface runoff,adjusting the layout of urban green space network and river system and improving its integration degree become an urgent approach to urban flood control.Taking zhengzhou city as an example,the use of a variety of spatial analysis and model simulation research means,landscape pattern of study area land evolution and its influence on absorbing runoff and rainwater storage,with the aid of the SWAT model building land use situation further simulated test,finally put forward the optimization of urban river water system,improve the urban green space alignment,blue Suggestions and strategies to improve the capacity of urban water intake and storage,improve the resilience of the city to cope with extreme weather.The main conclusions are as follows:(1)Urban expansion squeezes permeable ground,degrades river system and reduces landscape complexity.With urban development,the proportion of construction land increased from 8.37%in 1994 to 62.26%in 2020,becoming the main type of land use,which changed the landscape pattern of urban land.At the same time,the squeezing of construction land on green land,farmland and water permeable ground,on the one hand,leads to serious fragmentation and reduced complexity of landscape,reduces the infiltration and storage capacity of urban rainwater,and magnifies the impact of waterlogging disaster.On the other hand,the water surface of the river is reduced,the density is reduced,and the structure is single.The adjustable storage capacity of the river per unit area is reduced by 5198.60m3/km2.Although the intervention of artificial water conservancy measures in the later period alleviated the impact of urban development on river system,the restoration effect still lagged behind the urban development.(2)The rational layout of urban green space is an effective means to control surface runoff.The simulated surface runoff increased by 4.7 times from 1994 to 2020.Combined with the change of land use,the expansion of construction land promoted the formation of surface runoff,while the permeable green land and farmland weakened the surface runoff.According to Pearson correlation analysis of land landscape index and surface runoff in terms of patch types,green space has the greatest impact on surface runoff,with correlation coefficient sum of 2.123,followed by farmland and construction land type,with correlation coefficient sum of 1.794 and 1.294,respectively.At the landscape level,shannon diversity index(SHDI)was the most correlated,with a coefficient of 0.799.(3)Based on the concept of "source and sink" in air pollution prevention and control science,the threshold value is calculated as follows:Impervious construction land belongs to "source land",and permeable green land belongs to "sink land" The R2 values of R_SC,SHDI and annual surface runoff in different years were obtained by constructing the fitting equations of R_SC,SHDI and annual surface runoff,which indicated that R_SC and SHDI were strongly correlated with surface runoff.The results showed that R_SC increased by 1.246 from 1994 to 2020,which was in line with the rising trend of surface runoff.Compared with the acceptable water depth of roads in"Technical Code for Urban Waterlogging Prevention and Control",the proportion of construction land was about 21%,and the corresponding landscape index SHDI value tended to 1.10.By constructing different land use scenarios to further verify the green space for stormwater runoff reduction effect significantly,after comprehensively reflects the city continuous development at the same time,not only to optimize the structure of water system,more to regulate urban green space landscape,promoting the fusion of green fields and rivers can effectively reduce surface runoff,improve urban given runoff,improve the ability of water storage. |
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