Local Climate Zone-based Characteristic And Optimization Study Of Thermal Environment Of Urban Blocks In Hot And Humid Areas

In recent years,the long-term high temperature and high humidity in cities in hot and humid areas hinders the improvement of living quality,and responding to the global warming and urbanization problems has been becoming a core requirement for mitigating the local-scale thermal environment effect.Aiming at the climate-friendly city environment construction,unraveling the drivers of thermal environment in urban block unit is the key stage for realizing the climatic rationality of urban spatial form design.As a theoretical system linking urban spatial morphology and thermal environment characteristics,the “local climate zone(LCZ)” scheme provides a quantitative surface landscape classification standard for the current research field of urban thermal environment.At this stage,there are relatively few research cases involving the application of the LCZ scheme into the block-scale thermal environment.And a comprehensive analysis methodology that can accurately visualize the spatiotemporal distribution characteristics of the block-scale thermal environment is urgently needed.Therefore,taking the Higher Education Mega Center(HEMC)and Pearl River New Town(PRNT)in Guangzhou,China as the case regions,this study combines the methods of mobile measurement and numerical simulation to discuss and analyze the differences in thermal environment characteristics between different LCZ types and their associated factors under multi-temporal and spatial scales.Firstly,a block-based LCZ classification methodology that can provide data basis for quantitative factor analysis of thermal environment characteristics of urban blocks is proposed.The LCZ classification results show intuitively the spatial morphological differences between the HEMC and PRNT.Among them,the HEMC mainly characterized by open mid-rise buildings(LCZ 5),dense trees(LCZ A)and low plants(LCZ D)presents the spatial pattern characteristics of high space openness and wide coverage of pervious underlying surface.Whereas the dominant LCZ types for PRNT composed of high-rise and high-density building complex with narrow street canyon are compact high-rise buildings(LCZ 1)and open high-rise buildings(LCZ 4).The above two case regions include a total of8 built-types and 6 land cover-types of LCZs,providing a wealth of block samples for distinguishing the thermal environment heterogeneity.Secondly,based on the mobile measurement and spatial interpolation methods,this study analyzes the spatiotemporal distribution characteristics of daytime near-surface air temperature and relative humidity in the on-route mobile points and urban blocks respectively under different seasonal conditions.For time-varying characteristics,compared with transitional season and winter,the thermal environments of case regions at typical moments in summer presents a high degree of spatial heterogeneity.The results of spatial distributions show that the air temperatures of different LCZ types present the following regular characteristics.Among the built-type landscapes,the air temperatures of compact/high-rise buildings are lower than that of open/low-rise buildings,while for the land cover-type landscapes,the air temperatures of dense/scattered trees are lower than that of low plants,bare rock/paved road,bare soil/sand and water body.In addition,the lateral thermal interactions between urban blocks are reflected through spatial autocorrelation analysis,which indirectly demonstrates that besides its own spatial morphology,the location of urban block is also one of the factors leading to the thermal environment differences between the same type of LCZs.Additionally,aiming at exploring the application potential of LCZ parameterization scheme in the dynamic local-scale energy balance(DLEB)model,the dynamic time-series simulation research on air temperature and specific humidity of urban blocks in the HEMC in summer is conducted based on measured thermal environment data.The simulation results show that high-rise buildings have relatively lower air temperature values than other built-type landscapes and bare rock/paved road presents comparatively higher air temperature values,whereas water body and open buildings with wider range of pervious underlying surface have relatively higher specific humidity values.On the whole,the thermal environment differences between various LCZs are consistent with the measured results.It has been verified that there are a total average air temperature error within 1? and a total average specific humidity error within 2g/kg in the DLEB model,which is related to the setting of the physical property parameters from the LCZ scheme.Thus,this study establishes the corresponding multivariate nonlinear regression models to improve the simulation accuracy of air temperature and specific humidity.Finally,the correlation relationships between sky view factor(SVF),aspect ratio(AR),height of roughness elements(HRE),building surface fraction(BSF),previous surface fraction(PSF),impervious surface fraction(ISF)derived from the LCZ scheme and thermal environment parameter characterized by local-scale heat island intensity are respectively analyzed.The results show that the SVF and PSF are positively correlated with the local-scale heat island intensity while the AR,HRE,BSF and ISF are the opposite.Among them,there is a strong correlation between the HRE,AR and the local-scale heat island intensity.And the above correlation relationships are particularly significant in summer.From the identified thermal environmental problem areas,open mid/low-rise buildings,low plants and bare rock/paved road have greater thermal risk potential during the daytime,which can be improved by properly adjusting the building shadow area and space openness.In summary,conforming to the regional development of the LCZ scheme,this study systematically constructs a comprehensive analysis process for the multi-temporal and spatial thermal environment characteristics of urban blocks through the combination of field measurement and simulation.Then the corresponding spatial optimization strategies are given from the two dimensions of urban structure and land surface cover.From the perspective of urban spatial form planning and design,this study aims to provide the reference significance and technical support for improving the building indoor physical environment and realizing the building energy conservation and emission reduction.