Quantifying the uncertainty of urban heat adaptation impacts through a multi-model approach

Due to the projected impacts of climate change, there is increasing urgency to investigate how to adapt to potential increases of extreme temperatures, especially in cities. Several possible adaptation strategies already exist, but their complex impacts on urban temperatures remain largely uncertain. In our study, we investigate the reduction in temperature by different adaptation strategies and study the spatial variations in heat exposure across different Belgian cities. By using a multi-model approach, we aim to quantify the uncertainties related to the reduction of heat by different adaptation strategies and using different models.

The focus of our study is the extreme heatwave of July 2019, where temperatures reached 40°C in Belgium. We use a mini-ensemble of three urban climate models: the urban boundary layer model UrbClim at 100m horizontal resolution, WRF with the multi-layer BEP/BEM at 1km and COSMO-CLM with bulk urban land-surface scheme TERRA_URB at 2.8km. Three adaptation strategies are implemented across the three models: increasing vegetation fraction by decreasing built-up coverage, implementing cool roofs by increasing roof albedo, and a combination of both. This mini-ensemble allows us to characterize spatial variations in heat exposure across the city and to investigate the possible reduction of heat exposure by certain adaptation strategies.  Our model intercomparison improves our understanding of how different model parameterizations simulate the impact of different heat adaptation strategies and why each intervention may have different impacts in the different models. Lastly, we quantify the potential heat-reduction effects of the adaptations for local populations.