Rapid population growth accelerates urbanization, and human activities exacerbate climate change, leading to a series of urban thermal environment problems, especially in hot and humid regions. In China, regulatory planning is a crucial aspect of urban planning significantly impacting the emergence and development of urban thermal environment problems. However, the current methods for evaluating and optimizing the urban thermal environment at the regulatory planning level are relatively insufficient. In-depth study on the urban thermal environment at the regulatory planning level in hot and humid regions, assessment of the impact and risk of meteorological background on the environment and residents, and then regulation of the thermal environment through parameterization of planning control elements, can consider the urban heat island effect, thermal safety and thermal comfort, building energy consumption and other multi-objectives to effectively mitigate urban thermal environment problems.
Numerical simulation is an important way to study the urban thermal environment, and at the regulatory planning level, new models that combine multi-parameter and multi-objective evaluation are needed. In order to do this, this study shows how the algorithms and functions of the Urban Weather Generator (UWG) model can be made better and how they can be added to. In terms of algorithms, the radiant energy allocation algorithm for uniform three-dimensional rectangular building arrays, the roughness algorithm that takes into account vegetation, the vegetation energy allocation algorithm that takes into account weather, and the convective heat transfer calculation algorithm that improves the wind speed reference height are introduced. In terms of functions, the mean radiant temperature and the water temperature are extended. Following that, simulations are carried out using the improved and extended new UWG model in Guangzhou and Nanning, typical cities in hot and humid regions, and the air temperature, relative humidity, and mean radiant temperature at the regulatory planning level are evaluated using the measured data. The results show that the new UWG model performs well in predicting the trends and numerical results of the evaluated parameters (taking Guangzhou as an example, the coefficients of determination of the predicted air temperature, relative humidity, and mean radiant temperature are 0.966, 0.720, and 0.828, respectively, and the root mean square errors are 0.93 ℃, 6.59 %, and 2.34 ℃, respectively, and the mean bias errors are 0.10 ℃, 1.41 %, and −0.69 ℃, respectively), and the model has sufficient stability to simulate the changes in the thermal environment over long time periods.
To carry out urban thermal environment assessment at the regulatory planning level, it is necessary to parameterize various types of thermal environment information and conduct a comprehensive evaluation from multiple dimensions. In order to do this, this study proposes a multi-dimensional urban thermal environment information extraction and evaluation method and analyzes the central city of Guangzhou as an example. First, the thermal environment information is extracted from multiple data sources such as remote sensing inversion, visual interpretation, field research, and social perception by combining the Local Climate Zone (LCZ) system and building classification, and a thermal environment database is established for the central urban area of Guangzhou. Then, relevant thermal environment parameters were input into the new UWG model to analyze the thermal environment differences in the central area of Guangzhou from three objectives: urban heat island intensity, universal thermal climate index (UTCI), and building cooling energy demand. The research results reveal that there is some variation in the degree of superiority and inferiority of the thermal environment in each LCZ area under different thermal evaluation objectives, and the thermal environment of the area represented by LCZ 3 (compact low-rise building areas) is the most unsatisfactory. The global PAWN sensitivity analysis further shows that building height, building density, and wall-to-ground area ratio are the three factors with the greatest influence on the thermal environment, with their PAWN indices all greater than 0.2. Planning-related factors like urban morphology, blue-green infrastructure, anthropogenic heat from transportation, albedo, and building function type distribution have different effects on the thermal environment over time and space. By quantitatively analyzing each factor, the degree of influence and stability of the spatial and temporal variation of each factor can be developed into a targeted planning strategy to achieve the best thermal mitigation effect.
Uncertainty in the planning and design process could affect the thermal environment, which makes it harder to get the planning results that were wanted. To address this issue, this study constructs a multi-objective parametric thermal environment optimization design platform based on the new UWG model within the parametric plug-in Grasshopper in the planning scheme modeling software Rhinoceros 3D. The platform can evaluate the thermal environment at the regulatory planning level, provide suggestions on the values of planning control elements with full consideration of robustness, generate Pareto-optimal solution sets, and realize multifaceted evaluation and optimization of the thermal environment in the planning and design processes. Further, a climate adaptation planning process with the thermal environment as the core is proposed to incorporate the impact of the thermal environment into the decision-making process at the regulatory planning level. The multi-objective evaluation of thermal environment and parametric optimization applications is carried out with two regulatory planning cases as examples. The former compares the changes in urban heat island intensity, outdoor human thermal safety and comfort, and cooling energy demand for 8,760 hours of a typical meteorological year before and after the program modification and provides a quantitative method for comparing and selecting different control schemes from the thermal environment perspective. The latter provides an effective multi-objective parameterization method for optimizing the thermal environment by filtering out the thermal environment control units that need to be optimized based on the rapid calculation of multiple thermal environment control unit-related parameters, conducting a parametric search to obtain the Pareto-optimal solution set, and then outputting the corresponding proposed values of the planning control elements for the decision of the planner.
In summary, this study suggests a method for evaluating and improving the urban thermal environment at the level of regulatory planning. The method uses the new UWG model to extract multivariate urban thermal environment parameters based on the LCZ system and building classification perspective, constructs a multi-objective parametric thermal environment optimization design platform, evaluates the multidimensional impact of planning control elements on the urban thermal environment, realizes rapid, quantitative, and multi-objective regulation of the thermal environment at the regulatory planning level, and provides a theoretical basis and technical support for evaluating and optimizing the thermal environment at the regulatory planning level.