The Urban Land Surface Thermal Environment Dynamics And Optimization Recommendations

Natural land surface has been continuously transformed and replaced by artificial surface through urbanization, which is one of the primary contributions to the globally rising temperature. The LST governs the near surface water and energy balance, and thus modifies the urban microclimate. This makes the LST a special indication of land cover transformation, temperature increase and climate change. While planning and design professionals intend to optimize urban environment by modifying land surface composition and configuration, the LST is thus a significant environmental response of urbanization and urban planning. Planning and design may start with surface thermal environment problems to alleviate the stress imposed on environment by urbanization.Even planning and design professionals are familiar with several strategies of eliminating excessive heat, such as modify vegetation, pavements, and building geometries, there is no framework to support the strategies citywide from land use perspective. The study attributes the problem to the discrepancy of scale between urban meteorological research and planning and design implementation. The study proposes that the investigation of the LST phenomenon should be at local scale, where both the problems and strategies can be prioritized. On one hand, the zoning concept is employed to bring the LST investigation into conventional planning and design manner. The LST sensitive land surface indicators are extracted to classify the land surface into zones with homogeneous temperature patterns. On the other hand, the LST is examined at local scale as opposed to the city or regional scale characterized by the "urban-rural" dichotomy. Each place with excessive heat problems can be treated according to the land surface at the place comparing to its local surroundings. Specifically, this study involves analysis of the LST spatial dynamics through proper raster resolution scales, the zoning of urban land surface thermal environment, the extraction of local scale urban heat island, and optimization of the land surface environment. The study gives a framework to support problem identification and mitigation strategy recommendation.Firstly, reasonable analysis of the LST depends on proper selection of the raster image resolution in the scale space. The LST at different pixel scales reflects diverse patterns, which defines its spatial dynamics. Secondly, at the zoning stage, the Local Climate Zone scheme is modified to classify the land surface factors into zones. Thirdly, the LST is then analyzed at local scale to penetrate the restriction of conventional investigation of the temperature phenomenon. The mitigation strategies can then be more practical at this scale at the planning and design domain. The Multi-Scale Shape Index (MSSI) is then applied to characterize local patterns and extract local scale Urban Heat Island (LSUHI). To bring the temporal dynamics of the LST into consideration, those places with higher frequencies of being the LSUHI are named the hotspot, which may significantly impact the environment. The hotspot can be examined at any temporal scales, such as days, seasons and years. Such concern leads to more reasonable mitigation strategies. Finally, based upon the LTZ and hotspot characteristics, the mitigation strategies are proposed by comparing the land surface specifications of the hotspot and the corresponding LTZ. The process is explicitly problem oriented, which guarantees the applicability and practicability of the framework. The process contains the identification of the mitigation priority, and formalization of mitigation strategies through land surface specification.