The Synergistic Effect Of Urban Landscape Water Bodies And Waterfront Green Spaces On The Local Cool Island Effect

With the acceleration of urbanization,the urban heat island effect has brought serious hazards to the urban environment and residents’ lives.Utilizing urban blue-green spaces to reduce the temperature of the surrounding environment and generate local cool island effects is one of the most effective methods to alleviate the urban heat island effect.As a type of urban blue-green space,landscape water bodies and waterfront green spaces have a relatively stronger synergistic cooling effect compared to a single water body or single green space.However,the specific mechanism of the cooling effect of landscape water bodies and waterfront green spaces is not clear,and the quantitative analysis of their local cool island effect is still not comprehensive enough.Therefore,quantitatively analyzing the local cool island effect of landscape water bodies and waterfront green spaces,and exploring the synergistic impact of landscape water bodies and waterfront green spaces on the local cool island effect is of great significance to maximize the cooling effect.This study combines numerical simulation and remote sensing monitoring to quantitatively analyze the influence of landscape water bodies and waterfront green spaces on the local cool island effect.Firstly,different scenarios of landscape water bodies and waterfront green spaces are constructed using numerical simulation to analyze the cooling effect at different times of the day and factors affecting the cooling effect.Secondly,remote sensing monitoring is used to analyze the relationship between urban blue-green space landscape pattern indices and surface temperature at the landscape scale,and the relationship between landscape water body and waterfront green space patch characteristic indices and quantitative indicators of the cool island effect at the patch scale.The main research conclusions are as follows:(1)Both the proportion and layout of landscape water bodies have an impact on the cooling effect,while the impact of waterfront green spaces on the cooling effect varies with time.The impact of landscape water bodies on synergistic cooling effect is higher than that of waterfront green spaces.Through numerical simulation,it was found that when the proportion of landscape water bodies is greater than or equal to 16%,a cooling effect is present.As the proportion of water bodies increased,the cooling effect gradually increased,but the efficiency of improvement gradually decreased.When the water body proportion reached 64%,the cooling effect gradually reached saturation,with an improvement efficiency of less than 0.02 ℃ /%.In addition,appropriately increasing the distance between water body patches can make the patches have a synergistic cooling effect,and complex-shaped water bodies can increase the overall cooling effect of the surrounding environment.By analyzing the daily cooling effect of different waterfront green space scenarios,it was found that trees have a cooling effect,and the influence of vegetation planting on the cooling effect varies with time.The cooling effect is strongest when trees are planted densely in the morning under the transpiration of vegetation,while the vertical cooling effect parallel to the wind direction is strongest at night under the influence of wind environment.Overall,the impact of landscape water bodies on synergistic cooling effect is higher than that of waterfront green spaces.However,landscape water bodies and waterfront green spaces play different roles in synergistic cooling effect in different time periods,with the cooling effect of green spaces being strongest from 5:00 to 9:00,and the impact of waterfront green spaces on synergistic cooling effect being higher than that of waterfront green spaces.(2)The urban cold island pattern is closely related to water bodies and green spaces,and the landscape pattern of urban blue-green spaces has different impacts on surface temperature.In addition,there are differences in the effects of landscape water bodies and waterfront green spaces on the urban cool island effect at the patch scale.Using remote sensing monitoring methods,it was found that the urban cold island pattern in the area within the fifth ring road of Beijing shows a wave-like pattern with weak inside and strong outside,and the cold island is fragmented in the central urban area.The cool island pattern is closely related to water bodies and green spaces in the city.At the landscape scale,increasing the proportion of water bodies and green spaces,especially those with complex shapes and concentrated distribution,can significantly reduce surface temperature.Increasing the complexity and aggregation level of blue-green spaces also helps to reduce surface temperature.At the patch scale,the larger and more complex the landscape water bodies,the higher the coverage of vegetation and the stronger the connectivity,as well as the greater the distance from the waterfront green space to the river bank,the higher the intensity of the cold island.The larger the area of waterfront green spaces,the higher the coverage of vegetation,and the greater the distance from the waterfront green space to the river bank,the greater the range of the cool island.The more complex the shape of landscape water bodies and waterfront green spaces,the greater the cooling amplitude per unit distance,the higher the cooling efficiency,and the greater the cool island gradient.A predictive model was developed through stepwise regression analysis between the cool island effect and patch characteristic indices,and the model was validated.The correlation coefficients between the simulated and actual values for cool island intensity,range,and gradient were 0.693,0.571,and 0.639,respectively,indicating a high level of reliability of the model.