Assessing Aerosol-Induced Modifications of the Urban Heat Island in WRF Simulations for Paris: Findings from the WCRP CORDEX FPS URB-RCC STAGE-0

Understanding the interactions between urban areas and regional climate is crucial for improving climate projections and informing urban adaptation strategies. The WCRP CORDEX Flagship Pilot Study URB-RCC addresses this challenge through a coordinated modeling effort that evaluates urban climate processes using different regional climate models (RCMs) with urban schemes. As part of this initiative, STAGE-0 simulations focus on the Paris region during April–September 2020, capturing both a heatwave and a heavy precipitation event.

This study compares two simulations conducted with the WRF model by the Regional Atmospheric Modeling Group at the University of Murcia. The first experiment (CTRL) follows a standard WRF configuration used across modeling groups, integrating LANDMATE PFT land cover data with Local Climate Zones (LCZs), the BEP+BEM urban scheme, and aerosol climatology from MERRA2 reanalysis. The second simulation (CHEM) employs WRF-Chem, replacing prescribed aerosols with an interactive chemistry module that accounts for pollutant transport and interactions.

Both simulations reproduce the urban heat island (UHI) effect with reasonable accuracy. The inclusion of chemistry introduces notable differences in the daily cycle of urban-rural temperatures, generally leading to a cooling in both areas. However, these differences show a strong dependence on meteorological conditions. These findings highlight the role of aerosols and pollution in shaping urban climate simulations and emphasize their impact on the WCRP CORDEX FPS URB-RCC STAGE-0 simulations for Paris.

Acknowledgements: The authors acknowledge the ARUBA project (PID2023-149080OB-I00) of the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033). ERL thanks her predoctoral contract FPU (FPU21/02464) to the Ministerio de Universidades of Spain.