Impacts of urban adaptation on reducing temperatures and heat-related deaths in Belgium.

Extreme heat poses increasing risks to urban populations, yet the effectiveness of adaptation strategies at larger scales beyond neighbourhoods remains poorly quantified. The July 2019 heatwave in northwestern Europe, one of the hottest on record, offers a unique opportunity to evaluate city- and country-scale interventions in Belgium, in one of the world's most urbanised mid-latitude regions. Using high-resolution urban climate modelling, we investigated the benefits of adaptation strategies on urban air temperatures. Our modelling of urban air temperatures suggests that the widespread deployment of cool roofs could reduce daily maxima by 2.1 °C, while combining them with a 20 % relative increase in vegetation could lower daily minima by 1.7 °C. Here, we found substantial temperature differences between compact and open urban areas and, subsequently, in population exposure to extreme heat. Furthermore, we estimate that the implementation of cool roofs could have avoided around a quarter of all heat-related deaths during this extreme heatwave event in Brussels. Our results show that adaptation strategies must be tailored to local urban characteristics to achieve substantial reductions in temperature and mortality, with more compact urban areas benefiting most from cool roofs during the day while the combination of cool roofs and increased vegetation has more impact on reducing nighttime temperatures in open urban areas.