Active route choice to minimize pedestrian thermal discomfort in a high-density subtropical city

Overheating of cities is becoming increasingly critical due to the combined effects of urban heat islands and global climate change, impacting walkability and public health, particularly in high-density tropical or subtropical cities. While interventions such as shading and green infrastructure can mitigate street heat, their effectiveness is limited by resource constraints and the dynamic nature of urban microclimates. Most existing studies focus on streets themselves, overlooking how pedestrians actively select walking routes based on thermal comfort. This study proposes an active route bioclimatic choice framework that minimizes pedestrian heat exposure and discomfort. Using high-resolution microclimate simulation and exhaustive path generation, over 2.2 million pedestrian routes were created for 1200 origin-destination (O-D) pairs in a densely populated district of subtropical Hong Kong. A route-level thermal discomfort index, PetL, was developed by integrating Physiological Equivalent Temperature (PET) values exceeding a pre-defined discomfort threshold along each segment length. Results show that thermally-driven routes outperform shortest routes for 81 % of the O-D pairs, reducing thermal discomfort by up to 96 %. In contrast, simple shade-based routing proved unreliable, highlighting the limitations of shade as a sole criterion for pedestrian route selection. The effectiveness of thermally-driven route choice varied at different times of day, peaking in the early morning, and increased with both route length and permissible detour length, largely stabilizing at 700–800 m and 110 % of the shortest path, respectively. The approach presented in this paper can be embedded in pedestrian navigation systems to enhance walkability and reduce thermal exposure, especially for vulnerable urban populations, thereby promoting healthier, climatically adaptive, and more active urban living. A street renewal strategy is also proposed, prioritizing segments that are both thermally stressful and frequently used. The open-access dataset offers a robust foundation for future research.