Mediterranean region: Even drier by 2100

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'A new study suggests that the impact of climate change on the Mediterranean region will change precipitation and evaporation rates over land and sea, creating even drier conditions. A greater amount of atmospheric moisture will be lost from the region. Agriculture may suffer as a result, and the salinity of the Mediterranean Sea could increase. A range of climate change scenarios from the Intergovernmental Panel on Climate Change, IPCC-AR4 (2007)1, suggest that there will be major changes in precipitation (rainfall) in the Mediterranean region. The researchers, partly funded by the EU, as part of the CIRCE2 project, investigated the combined effect of decreasing precipitation and increasing surface temperatures over Mediterranean land and sea areas. Projections from a suite of climate models (CMIP3)3 were used.

The study suggests that many of the projected changes will have started by 2020-2049, with further changes gradually intensifying until 2070-2099. Land areas in the Mediterranean region will become progressively drier as rainfall decreases, with an 8 per cent decrease between 2020 and 2049. There will be about 15 per cent less precipitation in 2070-2099 compared with 1950-2000. As a consequence, soil moisture will also decrease, as will water runoff and the flow of water from rivers into the Mediterranean Sea. This means less water will be available for all other purposes, including irrigation. Although drier land surfaces mean lower rates of evaporation, the higher temperatures, which increase the rate of evaporation, will counter this. Overall, evaporation will decrease at around half the rate of the declining precipitation.

Long-term changes project a decrease in precipitation and an equal increase in evaporation over the Mediterranean Sea, resulting in an increase in the freshwater deficit of about 24 per cent (around 1.54 x 108 cubic metres) at the sea surface by 2100. Less water flowing from rivers into the sea (2.54 x 107 cubic metres) will contribute to further freshwater losses, possibly making the sea increasingly saline: the degree of salinity will depend on the inflow of fresh water from the Atlantic Ocean through the Gibraltar Strait.

Precipitation is expected to decrease by about 23 per cent during the dry season and by about 10 per cent during the wet season. At the same time, evaporation from the land is expected to decrease by about 12 per cent, mostly during the dry season. Taken together, these changes suggest that precipitation over the land will effectively decrease by an average of about 20 per cent over wet and dry seasons.

CMIP3 simulations for the 20th century suggest that the impact of increased greenhouse gas emissions may have already made the Mediterranean region drier and warmer. These simulations are consistent with the increase in regional aridity and the decrease in river discharge seen in actual observations.

The researchers suggest that the study could be limited by the current IPCC-AR4 climate models, which do not sufficiently capture the exchange of waters between the Atlantic Ocean and the Mediterranean Sea at the Gibraltar Strait. Next generation climate models should allow a better evaluation of this study's projections.'

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