Mediterranean water cycle changes: transition to drier 21st century conditions in observations and CMIP3 simulations

Under a suite of global climate change scenarios, the Fourth Assessment Report of the Intergovernmental Panel on Climate Change projects major changes in the Mediterranean region, in particular as a "Hot Spot" in hydrological change. However, the combined effects of future precipitation decrease and increasing surface temperature on Mediterranean water cycle, and in particular the impact on Mediterranean Sea water budget, are less well known. In this study we use the CMIP3 multi-model projections to show how individual hydroclimatic changes will concur to determine even greater alterations of future Mediterranean water cycle characteristics, with contrasting behavior over land and sea. We focus on the "transition phase" from recent past conditions to the much drier conditions expected at the end of the 21st century. By the end of the 21st century, models' average predicts a decrease in land-surface water availability and an increase in the loss of fresh water over the Mediterranean Sea due to precipitation reduction and warming- enhanced evaporation, with a remarkably high consensus among analyzed models. 20th century simulations indicate that the "transition" toward the projected conditions has already started to occur and has accelerated around the turn of the century. These tendencies are consistent with various observational evidence.