| Shanghai is located in Yangtze River Delta,with numerous river networks.The waterfront area is regarded as an important space for urban development.The ecological space in the waterfront area also has positive impact on urban microclimate.This paper has studied the microclimate characteristics of five typical block-scale green space patterns in waterfront area in Shanghai.This study aims to determine what kinds of green space morphology in waterfront area have good cooling effect.In this paper,five different typical green patterns at block scale were studied in Shanghai,including grid green pattern,green corridors pattern with west-east orientation,green corridors pattern with north-south orientation,scattered point green pattern,and radail green pattern.Microclimatic distribution of five build-up blocks with similar scale,building development intensity and green land rate from the northern shore of Suzhou river(three sites)and Dingpu river with same width(two sites)has been simulated,using ENVI-met4.4.5.A multidimensional spatial influence variable system was constructed to describe the spatial structural and morphological factors of the green space network and the boosted regression tree(BRT)model and the correlation analysis method have been chosen for studying microclimate environment in different green space pattern.To describe space network these variables have been used including: distance from water body,d PC,green space orientation.As to spatial morphology variables,indexes such as green corridor width,green space area,surface albedo,sky view factor(SVF),surface temperature and landscape pattern were used.(1)The result shows that water body and green have a significant effect for microclimate in both horizontal and vertical.River vapor and cool island could be distributed to 800-1000 meters away the river's edge by blue-green synergistic effect.Besides,the green space with great connectivity and width is more conducive to give full play to the blue-green synergistic effect to play the role of cooling,humidifying and improving human comfort perception for the riparian.The green's wind speed can be increased within 600 m from the water's edge when the height is over the tree.(2)Green connectivity has a positive effect for microclimate in horizontal and vertical direction.When the connectivity is over 1.0,a significant positive effect for microclimate will be observed.Green space in corridor shape has a better ventilating condition,therefore increasing width of green corridor between green patches could increase the green connectivity then improving the ventilation conditions.(3)When the green area shares the same direction with prevailing wind direction,the effect of cooling,humidifying and improving PET becomes more significant.As to green orientation in this research,green space in north-south direction has a more significant effect than green space in west-east direction.Green space sharing the same direction with prevailing wind direction or is perpendicular to river direction can distribute cool island better.(4)Environmental conditions like SVF,Surface temperature have important relevance with microclimate.When SVF is between 0.15-0.3,the larger value of SVF will lead to a less significant effect of cooling,humidifying and PET in both horizontal and vertical direction.(5)For the scale of green area,larger width provides better effect on cooling,humidifying and PET in both vertical and horizontal direction.Besides,a significant improvement of ventilating has been observed in vertical direction when width was increased.What's more,green corridor with the width between 20-30 meters has the greatest marginal effect of cooling.When green corridor's width is over 50 meters,the effect of cooling and humidifying from green space becomes constant.During the comparative study of five green pattern,the block with grid green pattern of the green space corridor consistent with the prevailing southeast to northwest wind direction and the green space corridor with the southwest to northeast direction where the microclimate effects is stable.This block's green space connectivity is considerable and the effect of cooling and humidifying is significant.However,the narrow width of partial greenbelt corridor is the key factor to limit its cooling effect.The block with green pattern mainly formed by west-east corridors is limited by surrounding buildings,and the affection range of microclimate in this block from blue and green space in west-east is limited.Therefore,enhancing green corridors in north-south direction could be a provable approach for this block to improve the whole green network's connectivity.The block mainly formed by north-south direction green space shares the same direction with prevailing wind direction has a wider green corridor,then the effect of cooling and humidifying would be promoted by cool islands from river and riparian green space.Improvements should be focused on enhancing the connectivity and width of west-east green corridor to accelerate the ventilating of green network in this block and achieving the target of enhancing the cooling effect by means of improving spatial structure.The block with scattered point pattern has a large amount of separated patchy areas and the worst microclimate effect.Considering these,improving connectivity and widening green spaces share the greatest priority for improving the microclimate in this block.The block with radail green pattern has green space corridors that are interconnected in each direction.Then this green space layout pattern can produce a more significant effect of cooling and humidifying in the horizontal and vertical directions.The green space in this block is more open than other blocks,then the microclimate of green space is less affected by building environment.The single index's marginal effect of the microclimate was compared and analyzed,and different thresholds and trends value of microclimate data in different indexes have been discussed in this research,which will provide useful perceptions for urban microclimate adaptive planning and design. |
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