Beyond the buffer: an activity-based approach to heat exposure assessment

Due to the global climate crisis, heatwaves will become more frequent and severe in the future, leading to direct and indirect negative health effects. Heat affects places differently, as a result of built environment characteristics, which lead to different outdoor microclimates. This makes it important to assess in what locations people are most exposed to heat. Existing approaches assess this exposure mostly based on residence-based buffers or administrative units, which comes with contextual uncertainties, since it is not known to what extent hot or cool locations are actually traversed by residents. This is relevant because microclimates are highly local, which may make area-based assessments inaccurate. This paper therefore proposes and develops a different method, focusing on routes from residences to daily destinations. Results show that the microclimate in buffers or neighbourhoods is only moderately related to this activity-based heat exposure metric. The presence of green infrastructure within a buffer is related to the relative difference between the two exposure metrics: if an area is greener, activity-based exposure is relatively underestimated, and vice versa. A possible reason for this is that green space is often not traversed by routes to daily amenities. The results of this paper can be used to more carefully prioritize interventions that improve protection from hot microclimates, specifically by providing cooling in locations traversed by a large number of people.