| The stormwater redistribution effect of urban green spaces can reduce runoff generation and delay peak runoff occurrence while also reducing the frequency and intensity of urban flooding disasters.Based on meteorological data(2016-2018),remote sensing data,field survey.Simulation data of i-Tree Hydro urban hydrological model.This study was conducted to investigate the effects of urban green space landscape pattern on vegetation canopy retention efficiency,the differences in rainfall redistribution effects of urban green space under different rainfall intensities,the differences in canopy retention effects of green space vegetation during the spreading and deciduous seasons,and the effects of rainfall ephemeris on vegetation canopy retention effects.Based on the above research,we further propose methods and approaches to optimize and enhance the redistribution effect of rainwater in urban green areas.The main research findings are as follows:1.In 2016,the annual stormwater retention and reduced stormwater runoff volume of urban green areas in Luohe City were 573,146 m3 and 122,637 m3.They account for 1.17%and 0.25%of the annual rainfall,respectively.The annual rainwater retention efficiency and annual runoff reduction efficiency of each urban green space differ significantly.The annual retention efficiency of park green space,protective green space,subsidiary green space,and square green space are 238.9,215.2,142.1,and 114.5 m3/yr/ha,respectively,and the annual runoff reduction efficiency is 51.1,46.0,30.4,and 24.5 m3/yr/ha.2.Each vegetation index(DVI,GNDVI,MASVI,NDVI,RNVI,and RVI)showed a significant exponential relationship with the vegetation canopy retention of the green space.Among them,NDVI can well explain the spatial variation of canopy interception of Greenland vegetation(prediction accuracy 88.8%),and the fitted model of NDVI and interception is RI=7.1*e8.94*NDVI3.The spatial variation of UGS CRI efficiency was big under same urban green cover ratio.When the green cover ratio lower than 45%,increasing the green cover ratio could promote the CRI efficiency remarkably,while the green cover ratio lower than 25%,the CRI efficiency could be increased by increasing landscape diversity.Under same green cover ratio,the increasing aggregation index of UGS could bring a higher CRI efficiency.When the green cover ratio above 45%,the CRI efficiency varied considerably and won't increase along with the increasing green cover ratio.There was a threshold value of green cover ratio,which limited the CRI efficiency increasing potential.4.The pervious cover in current and planning scenarios had an obvious capability to intercept and store rainfall,which could reduce the surface runoff directly.With the increasing rainfall,the pervious cover runoff production in planning scenario was higher than that in current scenario,which meant the rainfall storage was limited.The capability of rainfall interception,infiltration and storage could not increase along with the increasing rainfall,and the runoff reduction efficiency of current and planning scenarios decreased dramatically with the increasing rainfall intensities.The runoff reduction efficiency of current scenario was limited and had a similar trend with the planning scenario,high in low intensity rain events and low in high ones.5.The planning scenario with higher green cover ratio could intercept more rainfall than the current scenario.The CRI efficiency of the two scenarios could increase with the increasing rainfall under 10mm.While with the continuously increasing rainfall,the CRI efficiency reached to the peak and could not increase any more.The UGS CRI efficiency in leaf-on and leaf-off seasons varied a lot due the seasonalchanged.rainfall and LAI.UGS have a higher CRI efficiency by 3%to 13%in long duration rain events than that in short duration rain events.6.i-Tree Hydro and Eco models,which was developed by USFS,were used in this research to assess the hydrological ecological benefits of green spaces on the city scale and local scale.It was the first time that the model was utilized in China on a city scale to explore the role of urban green spaces on urban surface runoff regulation.i-Tree model was developed based on the environment in US,by revising and updating customized localized parameters in the model,the edited model was suitable to assess the hydrological ecological benefits in China. |
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