Urban Areas under Climate Change: What Regional Climate Models Reveal at Different Scales

Understanding interactions between urban environments and regional climate change is crucial for assessing the impacts of cities on the climate and vice versa. Regional Climate Models (RCMs) offer a promising tool to simulate these interactions over decades or even centuries. RCM developments have moved towards increasing grid resolutions down to kilometer scales, and therewith the city scale. However, a key question remains: How well do RCMs capture cities and their interactions with the regional climate?

The global Flagship Pilot Study “URBan environments and Regional Climate Change” (FPS URB-RCC), under the WCRP CORDEX initiative, offers insight into this question. Firstly, through analysing how RCMs depict urban climates across scales using existing global CORDEX-CORE (~25 km) and European convection-permitting (2–4 km) simulations. Secondly, through coordinated experiments the FPS assesses how different combinations of urban schemes and RCMs affect the results for the Paris region (France), encompassing over 30 simulations from 15+ modeling groups.

Key findings show that RCMs capture urban climate imprints, with higher-resolution simulations improving accuracy. Advanced urban schemes outperform simple bulk parameterizations, particularly for the nighttime urban heat island effect. Urban land-surface data quality is as crucial as parameterizations, yet RCMs globally underestimate urban land use, especially in Africa and Asia. Sensitivity experiments confirm the added value of integrating detailed urban data, such as Local Climate Zones (LCZs). Methods to extract urban areas and their surroundings from RCM data are advancing nevertheless remain challenging, especially across spatial resolutions.

Looking ahead, the next phase of FPS URB-RCC Paris region simulations and the Global Satellite Cities approach will extend investigations to longer time periods and urban areas globally, including vulnerable regions. 

In summary, the FPS URB-RCC demonstrates that RCMs can offer advanced urban climate projections and deepen our understanding of the relationship between cities and regional climate change.