Spatial variations in heat exposure and effects of potential urban adaptation strategies on heat-related mortality in Brussels: a case study of the 2019 heatwave

The urban heat island effect causes cities to experience higher temperatures than their rural surroundings. During heat waves, this phenomenon can amplify heat stress by exposing urban populations to more extreme temperatures than their rural counterparts. This can lead to increased heat-related mortality. With climate change expected to intensify heatwaves, cities are seeking effective adaptation strategies to reduce urban temperatures. However, key questions remain: which strategies should be prioritized, and where should these strategies be implemented?

We present the modelled impact of urban heat adaptation strategies on air temperature in Brussels during the Belgian heatwave of July 2019. Three adaptation strategies are tested: increasing street-level vegetation cover, enhancing roof albedo, and a combination of both. We use a mini-ensemble of three urban climate models (COSMO-CLM with TERRA_URB at 2.8 km horizontal resolution, WRF BEP-BEM at 1 km and UrbClim at 100 m) to simulate current conditions, the different adaptation scenarios and compare them to a scenario with no urban areas. With this approach, we identify temperature hotspots related to the presence of the city and quantify their role on heat exposure within Brussels. By applying an exposure-response function, we gain insight into deaths attributable to heat and, thus the impact of urban areas on heat-related mortality. Additionally, adaptation modelling assesses the reduction in deaths due to the implemented strategies. Lastly, the mini-ensemble improves our understanding of any gain from added complexity and resolution in the urban climate models.