ETH Grant - Neigbourhood resolved climate model

The Urban Heat Island (UHI) effect, characterized by higher air temperatures compared to the surrounding rural environment, threatens seriously our future urban comfort, inhabitant health and building energy consumption and is considered as one of the major problems in the 21st century posed to human beings.Due to the severity of the problem, major research initiatives have been directed to a better understanding of the physics of the urban climate with the aim of proposing mitigation measures. In this project, we focus on the understanding the origin of local heat islands, i.e. local hot spots that appear in the urban environment during heat waves. The overall goal of the project is to understand the interaction of different urban physical processes - wind flow, radiation transfer, moisture transport, evapotranspiration of vegetation, convective heat transfer at building and ground surfaces, heat conduction and storage in building materials, soils and water bodies, rain - at the neighborhood scale by performing numerical simulations. Currently, there exists mainly two classes of urban climate models, parametrized and resolved, the former taking into account higher scale effects, but simplifying the momentum, heat and moisture exchange processes in vertical direction, while the latter resolves these processes, but does not include impacts of higher scales, such as the UHI effect. The underlying idea of this project is to couple a multi-layer Urban-Parametrized Climate (UPC) model to a Neighborhood-Resolved Climate (NRC) model using a one-way nesting approach, as such taking advantage of both models allowing the study of the origin of local heat islands and the physical processes at play. First, a dynamic Neighborhood-Resolved Climate (NRC) model is developed and a parametric study is performed to analyze the most important physical processes determining local urban heat islands at neighborhood scale, mainly during heat waves. Then, the NRC model is coupled to a state-of-the-art UPC model, which consists of a parametrized urban canopy model incorporating vegetation and coupled to a mesoscale weather and climate model. A one-way nesting procedure is used and optimized with respect to blending parameters and time stepping algorithm. The NRC model is validated using well-designed wind and water tunnel experiments. Finally, the NRC model is used to analyze the origin of local heat islands at neighborhood scale, especially during heat waves, and to propose and evaluate mitigation measures.