Study On The Design Target Of Chengdu Sponge City Based On Multi-fuction Effect

With the rapid development of urbanization in China,many natural underlying surfaces in the city have gradually been replaced by urban underlying surfaces.This has led to a series of urban environmental problems,the most prominent of which are stormwater and urban urban heat island.To solving the above-mentioned urban environmental problems,China began to promote the planning and construction of the sponge city.In the two years of 2015-2016,30 sponge city pilots were identified,and the sponge city planning work was rapidly launched nationwide.At the same time,the sponge city related research has become a hot topic of concern for researchers.The multi-functional effects of the sponge city include three aspects: ecology,culture and economy.Among them,water resources management and urban heat island mitigation are related to the assessment target of the sponge city.Therefore,the quantitative studies of water balance and urban heat island are of great significance to achieve the sponge city multi-functiongal effects.At present,the volume capture ratio of annual rainfall which is the core construction index of annual runoff total control rate is often concerned in the actual construction process of sponge city.However,the different sponge city planning and design schemes that reach this index have different effects on urban water quantity and thermal environment.Firstly,the paper discusses the current sponge city planning and design goals and the composition of sponge city multi-effects.Secondly,analyzes the correlation between the sponge city with urban water balance and heat island effect.Finally,t Finally,the paper selects the sponge city planning and construction in Chengdu as the research object.Through the numerical simulation method,the paper analyzes the difference between the impact of the sponge city planning and design schemes on urban water balance and urban heat island effect that meet the control objective.The purpose of the study is to improve the scientificity of the sponge city planning and design decision.At the level of water management,the research first analyzes the water balance process of sponge city,then selects typical cases and proposes several design schemes that meet the design goals of sponge city.Through the numerical simulation of water balance,the basic elements of water balance of different schemes are compared.The study confirmed that the water balance process of different schemes reaching the sponge city design goal is significantly different.A sponge city design method based on urban water balance is proposed,and it is pointed out that the sponge city design should set more detailed water control targets according to local conditions,and optimize the design according to the water balance numerical simulation method.At the heat island mitigation level,the study first analyzes the correlation between sponge urban planning and urban heat island effect: sponge city planning effectively improves urban heat island effect by changing urban underlying surface composition to influence urban local microclimate and changing urban radiation and energy balance.Then,taking Chengdu downtown area as the research scope,set up two planning cases to achieve the sponge city management and control objectives in the downtown area of Chengdu,and use the mesoscale meteorological model WRF-UCM coupled with the urban canopy model to carry out numerical simulation research.The simulation results show that:(1)The Sponge City Planning has effectively reduced the urban heat island effect by increasing the city's underlying surface green roof rate,permeable pavement rate and greening rate to change the urban microclimate factors and urban energy allocation.(2)The different sponge urban planning cases that achieve the control objectives have different effects on the urban microclimate factors and the urban heat island effect.The specific performance is that the higher the water content of the urban underlying surface,the more obvious the inhibition effect on the heat island effect.At the end of the study,a sponge city planning method based on heat island mitigation target is proposed.It is proposed that the sponge city planning can quantify the impact of sponge city planning on urban heat island effect by means of meteorological numerical model,and assist the sponge city in planning decision.Based on the sponge city multi-effect model,this paper studies the effects of several measures to achieve the urban water balance and urban heat island effect from the two aspects of water management and heat island mitigation.The sponge based on urban water balance is proposed.The urban design method and the sponge city planning method based on the heat island mitigation goal;provide a quantitative analysis method for the sponge city planning and construction,making the sponge city construction more scientific.