Urban Heat Mitigation in a Tropical Climate: A Computer Simulation-Based Study in Townsville, Australia

Abstract

Urban Heat Islands (UHI) pose significant challenges to cities, particularly in tropical climates. This study evaluates various UHI mitigation strategies applied to the Central Business District (CBD) of Townsville using ENVI-met v5.5.1. Air temperature (Ta), relative humidity (RH), wind characteristics, Mean Radiant Temperature (MRT), and Universal Thermal Climate Index (UTCI) were assessed under various scenarios. Strategies investigated include increasing natural and artificial shading, altering pavement albedos, and adding green buildings. Results show that on average, Ta in the proposed scenarios were lower than the input data (up to 3.5 °C) except at 1 pm and 4 pm, due to the differences in the urban morphology between the two dataset locations. Adding buildings generated the worst results and negatively impacted night cooling. The other scenarios positively impacted Ta reduction on average (0 °C to 0.21 °C per hour). The built environment significantly altered wind patterns, and added buildings contributed to increased wind speed (up to 1 m/s during the hottest hours). The median MRT increased during the early hours surpassing the health stress threshold (57.1 °C) at 9am, condition which remained until 2 pm, decreasing afterwards. But importantly, an overestimation of MRT was observed due to the topographical characteristics of the site. This study reveals a misconception that the hottest hours are the most harmful to human well-being, as they may vary based on the local climate patterns. Results also demonstrate that while some strategies contribute to temperature reduction, challenges persist, especially during the hottest hours. This work advances UHI mitigation for tropical savanna climates, guiding sustainable urban planning.