The impact of heatwaves on human health and the maritime sector

The 2003 European heatwave caused unprecedented fatalities, highlighting society’s vulnerability to extreme thermal events. Recent summers in the Basque Country (2023, 2025) have seen a recurrence of intense heatwaves, including rising water temperatures and a direct impact on beach management and coastal operations, necessitating urgent assessment of their impact on the coastal maritime sector, an area often overlooked in occupational biometeorology. This study’s main objective is the identification of short- and long-term impacts, such as impacts on operational sites (ports, docks and cargo ships) and impacts on human health, respectively. We analyzed hourly meteorological data from several coastal stations in the Basque Country during the summer heatwaves of 2003, 2023, and 2025 (specifically August in this last summer). Air temperature and relative humidity were used to calculate the Heat Index (HI) according to the NWS scale, assuming moderate physical work under protective clothing and direct solar exposure, conditions typical for deck crews and stevedores. During the August heatwave in 2025 (13th of August-18th of August), the HI reached extreme temperature values for several hours in a row in parts of Bilbao, exceeding the occupational safety threshold. Heatwave days increased the frequency of extreme thermal stress hours compared to a normal summer baseline. Crucially, the end of heat-related high-pressure systems triggered a considerable increase in wave height variability and wind gusts within 24 hours, directly elevating the risk of maritime incidents (slips, falls, crane operations) during port operations and coastal navigation. Besides the direct impact, heatwaves pose a dual threat: acute and chronic occupational health risks (heat stroke, dehydration, cardiovascular strain, etc.) for maritime workers, and increased operational instability due to rapid ocean-weather variability immediately after the end of a heatwave. We propose integrating biometeorological thresholds into national and port-specific early warning systems for maritime safety, as well as raising awareness about labour health, informing relevant authorities that  certain jobs or individuals may be particularly vulnerable to heatwaves and related episodes. Meteorological warning/alert/alarm systems could be adapted to coastal labour, evaluating impacts on the sector, and decreasing or avoiding incidents.