Walking in the heat. A pedestrian-centric heat exposure modeling framework

Climate change is increasing the frequency and intensity of extreme heat events in cities, creating health risks and mobility issues while navigating urban areas outdoors. To identify where and when pedestrians face the highest heat exposure levels, we developed a Heat Exposure Index (HEI) that combines highresolution microclimate modeling with pedestrian activity along sidewalks. HEI is based on two components, namely heat hazard, calculated using the Universal Thermal Climate Index (UTCI), and pedestrian exposure, estimated through a probabilistic routing model that simulates walking trips between selected origin and destination points. Pedestrian volumes are calibrated using observed data and examined for three time periods, i.e., morning peak, midday, and evening peak. The method is applied in central Los Angeles during a heatwave, revealing significant spatial and temporal differences in sidewalk-level heat exposure. Higher exposure is observed near transit stations and commercial destinations, where elevated UTCI values overlap with high pedestrian activity, disproportionately affecting transit-dependent populations. By combining microclimate conditions with pedestrian mobility patterns, the HEI allows fine-grained analysis of heat exposure. Ultimately, this research offers significant insights for heat-resilient planning strategies that aim to protect pedestrians outdoors and mitigate uneven heat risks in cities.