The breezes that blow from the Western Mediterranean Sea to land are losing strength, also reducing their cooling role for cities such as Barcelona, Valencia, and Ibiza.
According to a study led by the Center for Desertification Investigations (CIDE), which analyzed 41 years of data from 39 meteorological stations in Spain, France, Italy and North Africa, the speed of the sea breeze has been steadily decreasing since the 1980s.
In a paper published in the journal Scientific Reports, the researchers say that this deceleration is even more pronounced during heat waves in summer, further increasing the impacts of this extreme phenomenon.
The scientists explain that sea breezes are driven by temperature differences between land and sea. During the day, the land warms faster than the sea. The hot air rises and “pulls” the cooler air from the sea, refreshing the coastal areas.
However, that dynamic is disappearing. The Mediterranean is estimated to be warming between 20% and 40% faster than the global average, which could lead us to think that the speed of the breezes would increase, given the greater temperature contrast.
“However, we observe that sea breezes are becoming weaker, although more frequent in times of the year when they are less common, such as winter,” explains Shalenys Bedoya-Valestt, the study’s first author.
Based on the analyzed data, the researchers calculate that the average speed of western Mediterranean sea breezes is today 11% lower than in the 1980s. If one looks only at the summer months, the reduction nearly rises to 13%.
The Balearic Islands and the Spanish Mediterranean coast are the regions where the reduction in breeze speed is most pronounced, at 17.6% and 17%, respectively.
The loss of strength of the breezes that blow from the Mediterranean exacerbates the effects of heat waves on land. According to the study, these extreme climate phenomena reduce the speed of the breezes by up to 10% on islands such as Corsica, Sardinia and Sicily.
In the Balearics, heat waves slow the breezes by 8%, while on the Spanish Mediterranean coast the speed reduction is 4.8%.
Scientists say we are facing a paradox: the above-average warming of the Mediterranean causes more heat waves which, in turn, further weaken the coastal breezes that would help relieve them.
“Our hypothesis is that global warming is changing the way air masses move, making the hot air of tropical continental origin become ‘trapped’ over the Mediterranean, leading to more frequent and intense heat waves,” explains Shalenys Bedoya-Valestt.
“That hot and dry air acts as a ‘lid’ over the region: it stabilizes the atmosphere and reduces the speed of the air movements that drive the breeze, weakening it,” adds.
Thus, weaker breezes aggravate warming in the Mediterranean region and also the heat-wave phenomena, with impacts also on human health, since pollution can become “trapped” and not dissipate, in addition to the direct impacts of extreme heat.
