Efficacy of possible strategies to mitigate the urban heat island based on urbanized high-resolution land data assimilation system (U-HRLDAS)

Abstract

Summer heat waves are a significant public health threat in China. This paper took Wuhan (one of the four hottest furnace cities in China) as an example to explore several strategies for mitigating the surface urban heat island (UHI), measured by the land surface temperature, including green roofs, cool roofs, bright pavements, and altered urban building patterns. The offline urbanized High-Resolution Land Data Assimilation System (u-HRLDAS) was used to conduct 1-km resolution numerical simulations, which also accounts for the effects of Wuhan’s abundant lakes on UHI evolution, with a dynamic lake model. The diurnal cycle and spatial distribution of simulated UHI were analyzed under different mitigation strategies. Results show that considering lake effects reduces daytime (nighttime) UHI intensity by about 1.0 K (0.5 K). Green roofs and cool roofs are more effective in mitigating daytime UHI than bright pavements. The maximum UHI reduction is about 2.1 K at 13:00 local time by replacing 80 % of conventional roofs with green roofs. The UHI mitigation efficiency increases with larger fractions of green roofs, and increased albedo of roofs and roads. In contrast to green roofs, cool roofs and bright pavements are ineffective during nighttime, changing the urban building pattern to mitigate UHI is effective throughout the day. “Height-driven building structure changing” (raising the building height while changing the fraction of impervious surface in each grid to keep the total building volume intact) can reduce surface UHI intensity by 0.4 – 0.9 K, and “density-driven building structure changing” (distributing building density uniformly and modifying the building height to make the total building volume unchanged) reduces UHI by 1.2 – 2.6 K. These results showed new insights in mitigating UHIs for mega cities, like Wuhan, and provides a practical guideline for policymakers to offer more habitable cities.