Analysis of local dynamics and associated urban heat island intensity over Paris during heat waves in an ensemble of convective-permitting climate simulations

Heat risks in cities are augmented by the urban heat island effect associated with the high density of buildings, the lack of vegetated surfaces and human activities. During heat waves, different ventilation conditions can occur, depending on large scale conditions and their interaction with the local boundary layer (Haeffelin et al., 2025). During hot nights, the sensation of suffocation is heightened when the ventilation is weak. During these stagnant conditions, the atmosphere is stable even in the city with a strong thermal stratification. The cooling effect of parks remains very local (due to reduced ventilation) and does not allow the surrounding streets to be refreshed (Haeffelin et al., 2025), intensifying the thermal contrasts between rural areas, parks, and streets (Céspedes et al. 2024).

It is therefore important to evaluate how the interaction between synoptic conditions and local dynamics and thermal stratification in the urban boundary layer are represented in available high resolution climate simulations during heat waves. The optimal objective is to have tools we can trust to assess how much the frequency of heat waves' nights with these increased health risks' conditions will evolve in future and if greening solutions can reduce the risk efficiently.

In this work, the existing convective-permitting simulations performed in the frame of CORDEX FPS "Convection over Europe" and EUCP project are analysed and compared with available observations around Paris area during the two major heat waves events in august 2003 and july 2006. This analysis may be complemented by simulations performed in the context of CORDEX FPS URB-RCC covering heat wave of august 2020.