Climate/Water-Cycle Feedbacks in the Mediterranean: The role of Land-Use Changes and the Propagation of Perturbations at the Regional and Global Scale.

Around the Mediterranean sea, deserts and desert-like conditions can be found in close proximity to a very warm sea and thus to a marine airmass with a high moisture content, e.g., the coasts of Morocco, Algiers, Tunisia, Libya, and Almeria in Southeastern Spain. These regions were covered with vegetation in historical times, e.g., during the Roman Empire, and in the case of Almeria, just 150 years ago, before the forests were used to fuel lead mines. The question is: did forest removal cause them to run a feedback cycle towards desertification? The reanalysis of results from seventeen EC research projects (Section 5) suggests that this could be the case. This work shows that the hydrological system in this region is very sensitive to land-use changes and, more recently, to air pollution effects as well. Both of these can combine to exceed critical threshold levels, e.g., the height of the cloud condensation levels with respect to the height of the coastal mountain ranges. This results in the loss of summer storms and tips the regional climate towards desertification and drought. The non-precipitated water vapour returns and accumulates over the Western Mediterranean Basin to heights reaching over 5000 m, for periods lasting from 3 to 10 days in summer. [ABSTRACT FROM AUTHOR]