Exploring the Cooling Potential of Sea and Estuarine Breezes (SEB) in a Mediterranean city’s summer climate

Sea and estuarine breezes (SEB) play a critical role for cooling air temperatures and enhancing thermal comfort during summer in coastal urban areas. This research investigates the dynamics and impacts of SEB in Lisbon (Portugal) by combining data from a mesoscale meteorological network comprising 80 stations with high-resolution wind field simulations during the thermal summer of 2022 (June 10 to October 8). SEB episodes were identified using criteria based on wind direction shifts: the disruption of prevailing northerly winds in the morning (Nortada), transitions to easterly or southerly directions (rotation between 22,6 and 292,5º), and the resumption of regional flow by late afternoon. Wind fields were modeled using GRAMM-SCI, initialized with ERA5 reanalysis data. Finally, air temperature, absolute humidity and thermal comfort (Universal Thermal Climate Index) anomalies (ΔT/Ha/UTCI_urb) were calculated to a reference site (the airport weather station) according to the distance to the riverfront area.  SEB at 10 m height, occurred on 31% of summer days, peaking in July and August, with an average duration of six hours (10:00AM – 4:00PM). Considering only the roughness effect of the city and the terrain, these breezes reduced air temperatures up to 4 km inland, with maximum cooling effects (-1.7°C) observed within 500m of the Tagus estuary. Absolute humidity increased by 4.2 g/m³ near the estuary, and UTCI values dropped by 2.2°C on typical breeze days, reaching 5.1°C during heatwave events, substantially reducing heat stress within 1.5 km of the riverfront. However, some riverside areas still experienced moderate heat stress, highlighting the importance of preserving SEB corridors through climate-sensitive urban planning. This study reinforces the importance of integrating natural ventilation processes into urban design to foster cooler and more liveable cities.