The Hydrological Cycle of the Mediterranean

Abstract

This chapter discusses results of current and future-projected water cycle components over the Mediterranean region. Results are presented from an ensemble of CMIP3 multi-model simulations (here after referred to as Mariotti) and from the Meteorological Research Institute’s (MRI) 20 km grid global climate model. Referred to as CMIP3 results are surprisingly close to MRI. The projected mean annual change in the rate of precipitation (P) across the region (for sea and land), is projected to decrease by the end of the 21st century by −11% and −10%, respectively, for the MRI and Mariotti runs. Projected changes in evaporation (E) are +9.3% (sea) and −3.6% (land) for JMA runs, compared to +7.2% (sea) and −8.1% (land) in Mariotti’s study. However, no significant difference of the projected change in P–E over the sea body is found between these two studies. E over the eastern Mediterranean was projected to be higher than the western Mediterranean, but the P decrease was projected to be lower. The net moisture budget, P–E, shows that the eastern Mediterranean is projected to become even drier than the western Mediterranean. The river model projects significant decreases in water inflow to the Mediterranean of about −36% by the end of the 21st century in the MRI run (excluding the Nile). The Palmer Drought Severity Index (PDSI), which reflects the combined effects of precipitation and surface air temperature (Ts) changes, shows a progressive and substantial drying of Mediterranean land surface over this region since 1900 (−0.2 PDSI units/decade), consistent with a decrease in precipitation and an increase in Ts (not shown). The last section of this chapter reports on components of the hydrological cycle from five climate model projections for the Mediterranean region. Three of these models have an interactive Mediterranean Sea (MPI, ENEA, Météo-France), and two are versions of the Met Office Hadley Centre regional model (HadRM3-MOSES2, HadRM3-MOSES1) with different land surface schemes. The focus of this section is upon changes in evapotranspiration, and how these changes could be important in controlling available renewable water resources (runoff). These r indicate that rainfall is projected to decline across large areas by over −20% in all of the models, although in the Météo-France model the central part of the northern Mediterranean domain, ie. southern Italy and Greece, has areas of increase as well as decrease. In pockets of Turkey, the eastern Mediterranean, Italy and Spain, projections from the MPI, HadRM3-MOSES2, HadRM3-MOSES1 and ENEA models are for decreases in summer rainfall of −50% or more. Consistent with the global model projections, each of the five high-resolution models simulate increasing temperatures and decreasing evapotranspiration and precipitation for much of the Mediterranean region by the middle of this century. The strongest and most widespread reductions in precipitation are projected to occur in the spring and summer seasons, while reductions in evapotranspiration are greatest in summer.