Sea breeze changes in the western Mediterranean mainly driven by climate warming (1981-2021)

The Mediterranean warming is reshaping land-sea temperature gradients and related weather phenomena driven by differential heating, such as sea breezes (SB). Despite their importance, the response of SB to climate change remains poorly understood due to a lack of long-term studies. Changes in SB characteristics could have significant socioeconomic implications, particularly for sectors like wind power and agriculture, through shifts in the hydrological cycle and associated reductions in summer storms. This work evaluates trends in the occurrence (days) and magnitude (near-surface wind speeds) of SB across the western Mediterranean basin between 1981 and 2021. Using an objective and robust method, we identified SB events from meteorological data collected at 39 stations spanning Spain, France, Italy, Tunisia and Algeria. Daily wind speed data were homogenized to analyze annual and seasonal trends. To explore the influence of Mediterranean warming, we examined correlations between SB characteristics and anomalies in key thermal variables, including surface and low-level air temperature, land-sea air temperature contrasts, sea surface temperatures, heatwaves and solar radiation. Our results reveal basin-wide increase in SB frequency but a reduction in intensity over all timescales since 1981. Approximately 60% of regional variability in SB occurrence is linked to increased solar radiation, while Mediterranean warming accounts for a seasonal increase of up to 10% in SB days per decade. Conversely, SB intensity has weakened, particularly in Spain and the Balearic and Eastern Islands. This weakening is thought to be caused by a reinforced thermal contrast, which explains 70% of the variability in SB magnitude, with heatwaves contributing an additional 10% to the decline.