| Under the background of global warming,it aggravates the harm to human beings caused by urban heat island effect.In the face of urban climate challenges,macro-level strategies,such as mitigation of human-induced climate change by reducing greenhouse gas emissions,are one of the main solutions to address climate change.Adaptive planning at the micro-level has gradually become a research hotspot in the scientific community.Many studies have shown that urban rivers and greenbelts play an important role in alleviating urban microclimate,but there are few studies on the influence of river width on river microclimate effects,and the study on the synergistic effects of rivers and greenbelts is even weaker.Therefore,these two aspects of research can not only enrich the river microclimate effect theory and the water-green synergistic effect theory,but also have practical guiding significance for the riparian vegetation greening strategy.Firstly,this paper investigates the distribution of rivers in Shanghai,and then,according to the relationship between river width and microclimate effect,three urban rivers with different widths are identified as empirical research areas.Secondly,this paper uses the microclimate simulation software ENVI-met to simulate the actual situation,riparian sparse forest grassland vegetation greening and riparian compound vegetation greening of these three types of river distribution residential areas,respectively.The model is verified by field measurement method,and the present microclimate pattern of these three types of residential areas is analyzed.Then,the effects of river width,riparian green space,riparian vegetation structure and residential space form on the river microclimate effect are analyzed.Finally,based on the above research results,the optimization strategies of riparian green space,riparian vegetation structure and residential space form are put forward.The results show that:(1)The humidification range of the river to the surrounding area is larger than the cooling range;the cooling range of the 12 m wideriver to the upwind direction is smaller,and the cooling range of the downwind direction to the downwind direction is 150m;the cooling and humidifying range of the 30 m wide river and the 60 m wide river to the downwind direction reach the northernmost part of the residential area.(2)The width of the river is negatively correlated with the average temperature of the water body,and positively correlated with the maximum cooling gradient and the maximum humidification gradient of the river,and when the river width is larger,the wind speed over and around the water surface of the river is also larger;the direct relationship between river and PMV is weak,but it can indirectly improve thermal comfort by affecting thermal environment and wind environment.(3)After afforestation of sparse forest grassland vegetation on the riverbank,the overall thermal environment of the residential area can be improved,and the effect of cooling and humidification on the downwind area of the river is greater than that of the upwind area;it has a negative effect on the wind environment of the residential area to a certain extent;it is beneficial to the thermal comfort of the whole residential area,especially to the area near the river bank.(4)After the riverbank is afforested with compound vegetation,the range of synergistic cooling and humidification is larger than that of sparse forest grassland vegetation greening;and proper planting of trees will increase the wind speed under the ventilation corridor;the overall thermal comfort of the residential area is also better,especially near the riverbank where the trees are densely planted,the PMV value of the residential area decreases most greatly.(5)Because of the different spatial forms of residential area,the overall cooling effect and the increase of the lower PMV area of riverbank sparse forest grassland vegetation scheme on 12 m wide river layout residential area are larger than that of compound vegetation greening scheme;the 30 m wide river layout of residential areas is the opposite;the two greening schemes of the river bank have the same increase in the area of the lower PMV on the 60 m wide river layout residential area,and have no effect on the average temperature;the effect ofriverbank compound vegetation greening scheme on the whole humidification,wind speed blocking and thermal comfort improvement of three types of residential areas is greater than that of sparse forest grassland vegetation greening scheme.In addition,the average relative humidity of residential area and the area of "humid" area increased the most in the 30 m wide river layout area,which are 0.11% and 3.95%respectively,and the average wind speed and "breeze" area in the 60 m wide river layout area decreased the most,which are 0.09m/s and 2.69% respectively.(6)Because of the different spatial patterns within the residential area,the microclimate impacts of rivers on the same offshore distance are different;In general,riverbank greening has more than 200 m synergistic cooling and humidification range for the three types of rivers,and the negative effect on wind speed at 200 m offshore is greater than that at 100 m offshore,and has a good improvement on thermal comfort at100 m offshore.(7)Based on the above research conclusions and other scholars’ research results,it is considered that the riverbank should increase the green space appropriately,the vegetation structure should be dominated by the combination of trees and grass,and the ventilation corridor should be created at the same time. |
