Assessment of the Urban Heat Island Effect in Paris under different circulation weather types

Urban heat island (UHI) effect poses a significant human-induced challenge to urban communities, jeopardizing their livelihoods. Amplified by the upward global temperature trends, as a consequence of climate change, the effects of UHI have increasingly become severe. This manifests in crucial social (e.g., increased heat-related illnesses and mortality rates, particularly affecting vulnerable populations), economic (e.g. difficulties of some groups to access to cooling infrastructure for mitigating heat stress) and environmental implications (e.g., higher heat stress on vegetation, increase risk of species loss, increase of ozone pollutant levels). The current study examined the daytime and nighttime UHI effect in the region of Paris from 1990 to 2022. The study presents a novel method for assessing UHI using readily available data from the NCEP-NCAR Reanalysis 1 dataset (at almost 1.8 km spatial resolution) and low computational resources, enhancing the feasibility of UHI monitoring and analysis. By integrating daily circulation weather type (WT) classification with UHI analysis, this study elucidates the influence of weather patterns on UHI events.  Results showed that the most common WT were the anticyclonic (A) and the cyclonic (C) with almost 25% and 10% of occurrence respectively, combined with two additional directional types: the Southwestern (SW) and the Western (W) type which account for around 10% of the total cases for both WT. The anticyclonic type predominance is mainly due to the migration of the Azores anticyclone towards the area of study which is linked with higher urban heat island intensities either for maximum and minimum temperatures, especially during the autumn season. These anticyclonic situations were mainly associated with anomalous daytime and nighttime temperatures and accordingly a broader extension of Paris region affected by the UHI effects. It should be noted that a highest UHI effect was found during summer and especially noticeably for the nighttime. The findings of this study highlight the escalating severity of UHI impacts, exacerbated by global temperature trends due to climate change. Overall, this study highlights the urgent need for proactive measures to mitigate UHI effects in urban areas, encompassing policy interventions, infrastructure improvements, and community resilience strategies. By comprehensively understanding the dynamics of UHI and its interactions with broader climatic patterns, stakeholders can develop targeted interventions to safeguard urban communities against the escalating challenges posed by UHI in the context of climate change.

Keywords: Urban Heat Island assessment, climate risks, impacts, Lamb Weather Types, spatial analysis, Paris.