How convection-permitting climate models improve the representation of urban temperatures in Europe

This study presents the first multi-model ensemble evaluation of the added value of km-scale (2-4 km) Convection-Permitting climate Models (CPM) for representing urban temperatures and Urban Heat Islands (UHI) across multiple cities, compared to coarser-resolution (12 km) Regional Climate Models (RCM). To this end, we analyze 21 CPM simulations driven by the ERA-Interim reanalysis from 2000 to 2009. The ensemble spans six families of RCMs with urban parameterizations of varying complexity, ranging from simple surface/bulk schemes with modified surface parameters, to dedicated Urban Canopy Models (UCM). We evaluate the potential added value of the increased horizontal resolution and improved urban representation of the CPMs compared to their respective driving RCMs. This evaluation is performed across six European cities where data from urban and rural meteorological stations are available. The study focuses on how well the models represent daily minimum and maximum temperatures, as well as UHI intensities, in winter and summer. The results show that all models incorporating an urban parameterization capture some urban signal; however, their performance varies from city to city. CPMs with dedicated UCMs or simpler bulk schemes that represent key processes (e.g., anthropogenic heat in winter or solar radiation trapping in summer) can better simulate UHIs. The added value for temperatures outside urban areas is limited, as RCMs already match observations well. However, it can be significant over cities when the increased resolution is combined with the adoption of a more complex urban parameterization in the CPM. While all urban CPMs in the ensemble can represent average UHIs, even the best ones struggle to capture extreme UHI intensities.