Observational and modelling study of coastal breezes and thermal comfort under heatwave conditions

The frequency and impacts of heatwaves have significantly increased in recent decades (1975–2020), with Spain experiencing a marked rise in the occurrence of these extreme events (Núñez-Mora, 2021). In coastal environments, sea breezes —driven by temperature gradients between land and sea surfaces— can play a crucial role in mitigating extreme temperatures. This study examines the impact of coastal breezes on thermal comfort during a heatwave period in the southwest of the Iberian Peninsula.

Coastal areas have undergone intense urban development, and approximately 60% of the Spanish population currently resides in these regions (de Andrés et al., 2017). Consequently, urban heat exposure is modulated by meteorological processes operating across multiple spatial (from meters to hundreds of meters) and temporal scales. Within cities, air temperature and humidity exhibit local variations over hundreds of meters, while wind speed and shortwave/longwave radiation show important microscale heterogeneity influenced by urban settlement.

In this work, we employ the Weather Research and Forecasting (WRF) model coupled with the urban parameterization WRF-Comfort (Martilli et al., 2024) to investigate the impact of coastal breezes on thermal comfort. A comprehensive set of numerical experiments is designed to assess the sensitivity of sea-breeze simulations to key model inputs, including large-scale atmospheric forcing, urban datasets with different levels of morphological detail, and alternative sea surface temperature forcings. Model results are evaluated through systematic evaluation with observational data from surface meteorological stations, radiosoundings launched at strategic coastal locations during sea-breeze conditions, and oceanic measurements from a buoy in the Gulf of Cádiz.

This integrated modelling–observational framework enables investigation of the thermoregulatory effects of coastal breezes and their influence on the vertical structure of the coastal urban boundary layer. The study highlights the importance of accurately representing large-scale forcing, urban characteristics, and air–sea interactions to improve coastal breeze simulation and its role in modulating thermal comfort. The results contribute to a better understanding of mesoscale interactions between urban environments and regional climate processes during extreme heat events, with implications for assessing and mitigating heat stress in coastal cities.