The synergistic effects of urbanization and an extreme heatwave event on urban thermal environment in Paris

Abstract

In late July 2019, an extreme heatwave swept across the European regions. This study focused on examining the collective impacts of urbanization and this extreme heatwave on Paris's thermal environment. To achieve this, high-resolution simulations were performed using the urbanized version of the Weather Research and Forecasting (WRF) model. The inclusion of enhanced urban canopy parameters and improved spatial resolutions significantly improved the near-surface meteorological variables and the spatial-temporal patterns of the urban heat island in Paris. The impervious surface sensitivity study revealed that during the full-day sunlight conditions and low wind scenarios that characterized the extreme heatwave, the urban underlayer contributed to a 0.4 °C rise in daytime temperature and 1 °C increase during nighttime hours in the downtown area. Among the various representative Local Climate Zones (LCZ) types in Paris, namely compact mid-rise, large low-rise, and sparsely built, the contributions to temperature increase were about 0.3 °C (0.7 °C), 0.3 °C (0.5 °C), and 0.3 °C (0.6 °C) for daytime (nighttime) temperatures, respectively. The surface energy budget analysis further indicated that the augmented heat storage within urban impervious surfaces is one of the main causes of the enhanced urban heat island effect, particularly during the nighttime periods during heatwaves.