What added value of CNRM-AROME convection-permitting regional climate model compared to CNRM-ALADIN regional climate model for urban climate studies ? Evaluation over Paris area (France)

The convection-permitting regional climate model CNRM-AROME was applied on a spatial domain restricted to the northern half of France for analyzing its performances in simulating the urban climate of Paris region, and its potential added value compared to the regional climate model CNRM-ALADIN. In addition to its fine horizontal resolution (2.5 km compared to 12.5 km for CNRM-ALADIN), CNRM-AROME has the advantage of integrating the urban canopy model TEB into its land-surface modeling system. A hindcast simulation was performed for the past period 2000-2017, following an evaluation configuration for which CNRM-AROME was driven by CNRM-ALADIN, driven itself by the ERA-Interim reanalyses. Long-term gridded observations with kilometric resolution allowed a fine spatial scale evaluation of the atmospheric variables simulated by both models. They showed in particular a significant overestimation of spring precipitation, but an improvement of summer precipitation in CNRM-AROME compared to CNRM-ALADIN. Above all, thanks to its horizontal resolution and the use of a dedicated urban model, CNRM-AROME was shown to offer significant added value for the simulation of urban heat islands, for the mapping of heat-warming areas, and for representing the effects of the city on precipitation. It is a promising tool to diagnose climatic and impact indicators at the city scale, and their evolution in a changing climate.