Trends of sea breezes over the Western Mediterranean basin,1981-2021: are they affected by large-scale atmosphericcirculation changes?

Abstract

Western Mediterranean sea-breezes are becoming more frequent during winter and less frequent in summer. Further, observed trends in the mean wind speed show a weakening of the sea-breezes in all time scales. These changes could have direct implications for the air pollution dispersion in winter, or for the hydrologic cycle and desertification due to the sea-breeze thunderstorm losses in summer; among other environmental effects.  The drivers and physical mechanisms that underpin long-term sea-breeze changes are yet to be understood, but the response of the atmospheric circulation patterns to the anthropogenic driven warming might be one of the main triggers for the increased occurrence over the Western Mediterranean basin. Recent studies focused on the Eastern Iberian Peninsula suggest that more frequent anticyclonic circulations might be behind the increase of sea-breeze occurrence in winter. This work aims to advance on the likely causes driving sea-breeze changes by investigating their relationship with the Jenkinson and Collison weather type classification. To do so, we will analyze homogenized hourly wind speed data from 40 weather stations across the Western Mediterranean basin (i.e., Spain, France, Italy, Tunisia and Algeria) for 1981-2021. Sea-breeze episodes will be identified by applying a robust automated algorithm based on objective criteria considering the large- and local-scale conditions. The sign, magnitude and statistical significance of the trends in the occurrence, wind speed and gusts of Western Mediterranean sea-breezes will be quantified, as well as for the Jenkinson and Collison weather type regimes. Finally, we will estimate the relationship between these sea-breeze parameters and the synoptic weather classification. This study will provide new knowledge about the historical changes and multidecadal variability of sea-breezes across the Western Mediterranean basin and its response to global atmospheric circulation changes.