Added value of convection permitting climate modelling in urban overheating assessments

As a consequence of global warming and rapid urbanization around the globe, the magnitudes and frequencies of extreme heat events (EHEs) are increasing and this trend is expected to continue into the future. In this study, the added benefit of modelling climate at convection-permitting spatial resolutions (grid spacing <4 km) is considered for a set of exterior climate and interior building simulations during EHEs in the urban areas of Ottawa and Montreal, Canada over the summer of 2018. The climate is modelled at two spatial resolutions: i) 25 km – typically considered for regional-scale climate modelling; and ii) 1 km. The results derived from modelling at each of these resolutions is compared in respect to their adequacy in predicting different measures of overheating outdoors as well as those within a typical single-detached home. The results clearly demonstrate that simulations undertaken at a 1 km resolution permit more accurately calculate the magnitude of overheating, whereas simulations completed at a 25 km resolution lead to an underestimation of overheating in about 95% of the urban grids within either of these two cities. These results suggest the necessity of using convection-permitting climate simulations for overheating assessments over the urban scale.