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Millán Millán

Climate in the Mediterranean basin: atmosphere-sea-land interactions URL:

Along the last 20 years, the results of several European projects have shown the loss of summer storms along the Mediterranean basin. Also, important differences have been detected between measurement stations of the interior and the coast, because while the yearly average precipitation in the coastline has not really changed, we have observed in the interior stations how it tends to decrease. Another significant data are the increase of torrential rains in general, and particularly in spring (when torrential events are higher).

Upon the perspective of this negative change in the precipitation regime, and according to the results of our research, we can confirm that the decrease of vegetation on the slopes of our mountains and the drying of wetlands in our coasts are contributing significantly to these climatic change processes. Synthetically, the humidity that arrives with the Mediterranean breezes needs an additional contribution of water vapor coming from the terrestrial surface to result in storms before being incorporated into the general circulation. If this contribution is insufficient, the storms will not trigger and the water vapor returns creating strata up to 5500 m above the Mediterranean Sea. In this case, our litoral mountains behave like orographic chimneys that connect the winds in surface with their return in altitude. These kind of accumulation cycles normally last 3 to 10 days in summer, and during these cycles, water vapor enhances the greenhouse effect of other contaminants as this is 47 times more effective than CO2 (E.g., ozone x 200); with all of this, the surface of the sea overheats as much as the terrestrial surface due to the loss of storms.

All these processes alter the historical climatic equilibrium in the western Mediterranean basin and changes it into a new dryer state. But on top of this, these local perturbations in the cycle can propagate to other regions along the rest of the basin, and this way, the accumulated water vapor migrates towards the east of Europe provoking the floods that have been registered in summer in Romania, Austria, etc. But the most important fact is that with these changes in the Mediterranean,  also the Atlantic current of salt water is altered and increases, affecting this way the transition of the frontal Atlantic systems that no longer go into the peninsula (we loose storms, drought increases) and move north causing more intense rains in Ireland and Great Britain during the autumn. This means that the perturbations are transported to regions other than the Mediterranean basin.

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