Research On Spatial Forming Mechanism Of Urban Heat Island And Its Mitigation Countermeasures -a Point Of View Of Urban Planning

With global warming and the emergence of extremely abnormal climatic phenomena, such as, rainstorm, hurricane, high temperature, etc, people pay more and more attention to natural environment. The negative effects of human activities on environment have been scientifically proven. Urban heat island effect (UHII) is the prominent phenomenon of human activities on climate, which brings many threats to atmospheric environment, creature activities and human health and so on, as well as consumes a great amount of energy. Therefore, making quantitative and qualitative research on UHI will help prevent urban environment degeneration, reduce energy consumption and realize the sustainable development of human dwelling environment.Literatures on UHI mainly focused on five aspects, involving the forming mechanism of UHI, the spatial and temporal distribution, the mitigation measures of UHI, the potential of mitigation and social and economic assessment, modeling UHI. Though deep enough, former research is lack of system and integrity and the research result is lack of universal operation and guide significance due to the obvious local characteristics of UHI.Based on former research, the paper studied the spatial forming mechanism of UHI and planning mitigation countermeasures both theoretically and practically, and proved part of the theory by taking Hangzhou as an example.In theory, first, the paper analyzed the spatial forming mechanism from three scales, that is urban, block and building scale. On urban scale, different land use/cover, urban form, urban function layout and vegetation cover are the macro-factors influencing UHI; on block scale, block surface cover, block form, street canyon are meso-factors influencing UHI; on building scale, materials of building roofs and walls, roof greening, building design and building envelopment structure are micro-factors influencing UHI. Then, the paper put forward planning mitigation countermeasures to different spatial scales. On urban scale, we should choose compact and polycentric urban development pattern, make urban energy planning, consider heat environment comfort during urban color planning, and improve the effect of urban green planning on environment; on block scale, use high albedo pavement materials, create open spaces, improve street canyon design and planting place; on building scale, use high albedo material for roofs and walls, green roofs with option, design architecture scientifically, and strengthen the heat performance of building envelopment structure. Finally, the paper constructed the technical process and countermeasures which included four steps: (1) analyze the relationship between UHI and multi-scale spatial surfaces; (2) identify different spatial factors influencing UHI; (3) forward planning mitigation countermeasures based on step (2); (4) make relative policies, laws and standards as safeguard measures.In the case study, Landsat5 TM sensing data are used to retrieve land surface temperature of Hangzhou and analyzed quantitatively the UHI characteristics from urban and block scales which proved and deepened part of the former theory discussion.