Building Resilient Cities for Heat Waves

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As projected by IPCC (with higher confidence compared to other weather extremes e.g., precipitation, cold, extremes), heat waves (HWs), excessively hot periods, are likely to occur more frequently, with higher intensities, and with longer duration, in the coming decades. Cities differ from their surroundings in terms of built forms, materials, and intensive anthropogenic activities. These differences result in the well-known urban heat island (UHI) effect, whereby cities are often warmer than their surroundings. HWs are exacerbated by the UHI effect and cause cities to be more vulnerable to HWs resulting in greater thermal stresses for urban residents. This is of particular concern for those residents susceptible to heat-related illness, given the intensified HW scenarios in the near future, and worldwide with more people living in urban environments. As such, building resilient cities for HWs warrants urgent attention. Resilience is "the capacity of a community or society to adapt when exposed to a hazard". In order to build resilient cities for HWs, the key is in understanding the responses of cities to HWs under varying scenarios: as climate changes, the climate extremes may also vary, which forces the urban systems through a "dose-response" function and subsequently leads to different biophysical impacts. The "dose-response" functions between climate and biophysical impacts in cities are essentially determined by the urban-atmospheric interactions, where the surface energy balance is one of the keys to greater understanding.In this Fellowship, I will employ both modelling and observational approaches to investigate the urban-atmospheric interactions as well as the urban surface energy balance under HWs. An adaptable tool, the analytical urban climate (ANUC) framework, will be developed for better understanding the urban-atmospheric interactions under heat waves. Compared with other popular numerically-based urban climate models, the ANUC framework features analytical rather than numerical expressions of various climate variables, which relieves the framework from expensive computational burdens and facilitates the exploration of as many HW scenarios as possible. The observations will emphasise the urban-rural contrasts in surface energy balance by constructing urban-rural flux observation pairs worldwide, the results of which are expected to allow generalisation of the urban-rural characteristics of the surface energy balance under different climates. Based upon the ANUC framework and the global urban-rural SEB characteristics, I will justify the effectiveness of different engineering approaches for mitigating thermal stress under HWs of the present-day and future climates by conducting many ANUC simulations.This Fellowship will shape a better understanding of the dynamics between cities and the atmosphere under HWs and will assess the effectiveness of mitigation strategies of cities under present-day and future climates, which will help building up HW resilient cities of the future.