Climatic Feedbacks and Desertification: The Mediterranean Model

March 2005

M. M. MillánaM. J. EstrelaaM. J. SanzaE. MantillaaM. MartínaF. PastoraR. SalvadoraR. VallejoaL. AlonsobG. GangoitibJ. L. IlardiabM. NavazobA. AlbizuricB. ArtíñanodP. CicciolieG. KallosfR. A. CarvalhogD. AndréshA. HoffiJ. WerhahnjG. Seufertk, and B. Versinok

aFundación CEAM, Valencia, Spain
bUniversidad del País Vasco, Bilbao, Spain
cEnvironment & Systems, S.A., Bilbao, Spain
dCiemat, Madrid, Spain
eIstituto di Metodologie Chimiche, Area della Ricerca del CNR di Montelibretti, Monterotondo Scalo, Italy
fAtmospheric Modelling and Weather Forecasting Group, University of Athens, Athens, Greece
gInstituto de Meteorologia, Lisbon, Portugal
hInstitut für Umweltphysik, Universität Bremen, Bremen, Germany
iAerodata AG, Braunschweig, Germany
jInstitut für Meteorologie und Klimaforschung, Bereich Atmosphärische Umweltforschung, Garmisch-Partenkirchen, Germany
kJoint Research Centre, Ispra, Italy


Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoon-type regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Mediterranean cyclogenesis and torrential rains in autumn–winter. Because these intense rains and floods can occur anywhere in the basin, perturbations to the hydrological cycle in any part of the basin can propagate to the whole basin and adjacent regions. Furthermore, present levels of air pollutants can produce greenhouse heating, amplifying the perturbations and pushing the system over critical threshold levels. The questions raised are relevant for the new European Union (EU) water policies in southern Europe and for other regions dominated by monsoon-type weather systems.

Author: Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.