Causes of Increasing Aridification of the Mediterranean Region in Response to Rising Greenhouse Gases*

Abstract

The hydrological cycle in the Mediterranean region, as well as its change over the coming decades, is investigated using the Interim European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) and phase 5 of the Coupled Model Intercomparison Project (CMIP5) historical simulations and projections of the coming decades. The Mediterranean land regions have positive precipitation minus evaporation, P − E, in winter and negative P − E in summer. According to ERA-Interim, positive P − E over land in winter is sustained by transient eddy moisture convergence and opposed by mean flow moisture divergence. Dry mean flow advection is important for opposing the transient eddy moisture flux convergence in the winter half year and the mass divergent mean flow is a prime cause of negative P − E in the summer half year. These features are well reproduced in the CMIP5 ensemble. The models predict reduced P − E over the Mediterranean region in the future year-round. For both land and sea, a common cause of drying is increased mean flow moisture divergence. Changes in transient eddy moisture fluxes largely act diffusively and cause drying over the sea and moistening over many land areas to the north in winter and drying over western land areas and moistening over the eastern sea in summer. Increased mean flow moisture divergence is caused by both the increase in atmospheric humidity in a region of mean flow divergence and strengthening of the mass divergence. Increased mass divergence is related to increased high pressure over the central Mediterranean in winter and over the Atlantic and northern Europe in summer, which favors subsidence and low-level divergence over the Mediterranean region.

Climate change in the Fertile Crescent and implications of the recent Syrian drought

“…The attribution to anthropogenic causes is also supported by climate theory and previous studies (see Supporting Information). Fortunately for this line of argument, this is a region where models compare reasonably well with 20th century observations in terms of simulation of the climatology of precipitation and its trend (44). The strong agreement between observations and climate model simulations in century-long trends in precipitation, temperature, and sea-level pressure (Fig.…”

Impact of large-scale circulation changes in the North Atlantic sector on the current and future Mediterranean winter hydroclimate

“…Strengthening of anticyclonic circulation in this region will presumably increase stability and create conditions less prone for the generation of cyclones (Giorgi and Lionello 2008). Seager et al (2014) argued that this strong anomaly localized over Italy and the Balkan Peninsula, seen also in a low-level high, increases subsidence and mean flow moisture divergence leading to strong drying in the region. Increasing warming contrast between land and ocean, present even in much earlier versions of general circulation models (Manabe et al 1990(Manabe et al , 1991, could amplify the drying tendencies in the Mediterranean region.…”

Homokhátság - a special rural area affected by aridification in the Carpathian basin, Hungary

“…The climate change models show that the mean annual precipitation will decrease in southern areas of Europe and drought periods will be more frequents (Seager et al 2014) and there will be an increase of mean annual temperature too (Kertész -Mika 1999;Kertész et al 2002). The situation is already very challenging for the ecosystem and the local society too.…”