Warmer seas and shifting pressure systems: The signs that suggest the Mediterranean's climate is 'tropicalizing'

The Mediterranean region is experiencing climate changes that suggest it is transitioning towards a warmer, tropical climate. This phenomenon, known as tropicalization, is evident in rising air and sea temperatures, shifting atmospheric patterns, and increasingly erratic rainfall. The average temperature in the coldest month across the Iberian Peninsula and the Balearic Islands is not yet high enough to qualify as tropical, but several signs point to a gradual shift.

Winters are becoming shorter and summers longer, with spring arriving earlier and autumn delayed. The temperature of both shallow and deep Mediterranean waters has risen significantly, with some areas exceeding 30°C, comparable to those in the Caribbean and Gulf of Mexico. Major wind belts and pressure systems, including the belt of tropical and subtropical high-pressure systems, are moving northward due to the expansion of the Hadley cell, a global-scale atmospheric circulation.

This shift could lead to increased atmospheric stability and less predictable rainfall, with long dry spells interrupted by heavy downpours. Warmer sea temperatures have also expanded the potential areas for hurricane formation, as the minimum surface temperature required is now being met in large parts of the Mediterranean. Additionally, low-pressure systems resembling tropical cyclones, known as medicanes, have been observed in the Mediterranean.

While the exact frequency of these events is still under review, the characteristics of these storms, including their warm core and spiral cloud structure, suggest they may be linked to the region's tropicalization. Along the Mediterranean coast, torrential rainfall is caused by various atmospheric conditions, including cold drop rains, persistent easterly winds, cyclogenesis over the sea, and mesoscale convective systems.

The complexity of the Mediterranean's geography and weather patterns makes it challenging to forecast weather accurately. In recent years, the difficulty in predicting rainfall intensity and the unexpected, erratic movement of weather systems has increased, posing a significant challenge for forecasting services. These challenges necessitate updates to forecasting procedures, a focus on intermediate and local spatial scales, and the incorporation of local observations through citizen science initiatives to improve public perception of risk.