How does the development of cities influence regional climate? A case study on the Paris region with the Convection-Permitting Regional Climate Model CNRM-AROME.

Cities constitute a crucial issue in the current and future environmental challenges, and they are highly exposed to extreme events, particularly high heat for the Paris region. This calls for a fine and explicit representation of cities in climate models to identify spatial disparities of the impacts of climate change. The Convection-Permitting Regional Climate Model CNRM-AROME (2.5 km) coupled to the TEB urban canopy model is suitable to conduct impact studies at city- and region-scale, considering climate evolutions. 

However, spatial dynamics of cities, such as urban sprawl or densification, are not represented in CNRM-AROME. Currently, the ECOCLIMAP-I land use map, based on CORINE Land Cover pan-European data from the 1990s, is used to characterise the surface properties, whether for simulations in present climate as well as for future climate projections. 

With the Paris region as a case study, three climate simulations of the past period 2000-2022 were carried out with the CNRM-AROME model, according to three land use scenarios (urbanisation of 1990, 2018 and 2050). These simulations allow us to quantify the effect of urbanisation on regional climate and its contribution on the warming trends in the Paris region. By a comparison with available observation data, we also assess the added-value of the actualised land use map against the default one. These results underline the importance of taking urban dynamics into account in the regional climate models, to better map the local impacts of climate change over urban areas and their surroundings.