| The rapid development of urbanization leads to the accelerated evolution of landscape pattern.Climate change and extreme rainfall often cause frequent alternation of drought and flood disasters in Dengfeng City.The imbalance of land use structure and disorderly urban development also pose potential threats to regional security pattern and sustainable development.Based on remote sensing images from 2003 to 2021,land use type and landscape pattern indexes were extracted in Dengfeng City.SCS-CN hydrological model,spatial autocorrelation analysis,Pearson correlation analysis and GWR model were used to explore the correlation between landscape pattern evolution and surface runoff and the spatial heterogeneity of the influence of variables.It was found that the flood detention capacity of forest lands decreased with the increase of rainfall,and towns along Ying River were faced with high risk of flooding due to the lack of corresponding rainwater storage system under extreme rainfall.In addition,the higher the spread connection degree of forest patches,the stronger the absorption effect on surface runoff.Therefore,the connectivity of green permeable space such as woodland,grassland and river wetland can be increased to reduce the risk of high runoff in the region.Based on the above conclusions,first of all,the coupled Arc GIS platform identified the inundating ranges of different precipitation periods and converted them into resistance surfaces to be incorporated into the ecological corridor construction process.Moreover,connectivity analysis was adopted to screen out the optimal diffusion distance when the network connectivity was maximum.Secondly,the key obstacle points and clip-points of corridor are identified by circuit theory,and the construction strategy of Blue-Green Infrastructure(BGI)network in Dengfeng city is put forward from three dimensions of city,township and river in combination with the current conditions of waterlogging vulnerable areas in Dengfeng city.At the urban scale,the rain and flood damage high pressure areas in14 catchment areas were identified and the waterlogging risk level control measures were put forward.Based on the layout of 56 potential blue-green corridors,the blue-green infrastructure network and important ecological source areas were divided into different protection levels,and the administrative district was taken as the management unit to formulate classified management and control strategies,systematically improving the stability and connectivity of the blue-green network in Dengfeng City.On the zoning scale,the identification of key ecological nodes of the green corridor defined the protection and planning strategies of each township for the clip-points and obstacle points,established a unified ecological flood control planning goal,and broke the administrative barriers that hinder the cooperative progress of each township.In terms of river spatial scale,in view of the current situation of river channels in flood prone areas and the disadvantages of traditional blue and green line planning,the protection scope of"blue line"should be increased and the integration design of blue and green space should be emphasized to improve the storage capacity of river channels for rainwater resources.This paper reveals the coupling relationship between landscape spatial distribution pattern and hydrological process in Dengfeng City,takes the difference of the impact of woodland connectivity on surface runoff in different precipitation periods as the entry point,establishes Dengfeng BGI network by identifying potential green ecological network and combining with blue corridor,and provides reference for exploring the feasibility of future urban stormwater management based on BGI strategy.It also provides theoretical support for the planning of rainwater resource regulation and urban flood control resilience in Dengfeng.The main results of the study are as follows:(1)From 2003 to 2021,the land use structure of Dengfeng City is always in dynamic change,reflected in the game among construction land,cultivated land and forest land;The cultivated land area continued to decrease and the construction land continued to increase.The decrease of cultivated land area from 2003 to 2009 accounted for 72.4%of the total change.The growth trend of construction land was from slow to urgent,and the forest land area increased first and then decreased.The transfer of land use types resulted in the complex evolution of landscape pattern.The LSI and IJI increased year by year,and the LSI increased significantly from 2003 to 2009 and from 2015 to 2021.Under the influence of"conversion of farmland to forest"and urbanization development,the landscape pattern in the study area continues to be complex,the connectivity of similar patches decreases,and the degree of landscape fragmentation increases.(2)The maximum surface runoff increment of Dengfeng City from 2003 to 2009,2009to 2015 and 2015 to 2021 was 12.69 mm,46 mm and 140.68 mm in dry,normal and wet month,respectively.That is,the runoff increased significantly with the increase of rainfall and urban development.In the 14 catchment areas,the average rain flood reduction rate decreased gradually in dry,normal and wet month,which were 94.42%,80.85%and 47.46%,respectively.In other words,the flood detention capacity of forest land decreases with the increase of rainfall,and it becomes the second largest fluid production under the construction land in wet month,which led to the construction land of 9.10 km~2 in the flood month,and the flooded area of the town located in the flood high pressure area expands from 0.29 km~2 in the dry month to 3.13 km~2 in the wet month.(3)At the landscape level,the correlation between landscape index and runoff was gradually significant with the increase of rainfall.SPLIT,IJI and LSI were all positively correlated with runoff,and the correlation between SPLIT,CONTAG and IJI in wet months decreased by 10.8%,12.3%and 8.3%,respectively,compared with that in flat months.At the patch type level,the larger the patch area of construction land and the higher the degree of combination,the significantly positive impact on the increase of surface runoff,while the degree of forest land combination and the increase of surface runoff were significantly negatively correlated,and the negative correlation reached the maximum in the normal month.(4)The influence of landscape index CONTAG,IJI and LSI on runoff in normal month is significantly different in both spatial and temporal dimensions.In the study area,there are positive and negative values,and the proportion of negative values is small.Overall,it is a positive driving force,and the dominant driving force changes from IJI to CONTAG over time.For example,the area with construction land as the dominant connectivity patch has a significant positive driving force on the increase of runoff,while the area with forest land as the dominant patch has a significant negative driving force on the increase of runoff.(5)Landscape types such as the core area were identified by MSPA analysis method.The optimal edge width parameter applicable to Dengfeng City was 90 m,and the core area was201.77 km~2,accounting for 34.36%of the total ecological elements in Dengfeng City.The connectivity analysis results show that the key diffusion distance threshold of the ecological corridor in Dengfeng City is 14.1 km,and the whole landscape network constitutes an ecological patch with the largest connectivity.The circuit theory results show that the excessive corridor"width"will cause the disappearance of some sandwiching points.The optimal corridor"width"(CWD)in Dengfeng City should be 3×10~4,and the area of key"sandwiching points"reaches the maximum.(6)The study identified 26 important sources,4 general sources,56 potential corridors,107 key obstacle points and 14 important pinch points.The source area is generally distributed in the north and south mountains of Dengfeng City,mainly in large area of ecological land,forming a pattern of"north and south facing each other".The corridors connecting the south and north source areas are evenly distributed in the transverse space,but the corridors are long and have multiple interchanges with the river corridor,which lacks ecological patches with stable blue-green network connectivity.The key corridors in the southeast of Dengfeng City are narrow and have high current density.Many important pinch points are adjacent to the construction land,and each corridor has multiple key obstacle points.Most of them are urban buildings,traffic roads and abandoned mine pits. |
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