Mediterranean-style climates to get drier under climate change

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Regions around the world known for Mediterranean climates will become much drier in the future unless greenhouse gas emissions are cut, a new study has revealed.

Scientists from the UK and Italy published their study in the Proceedings of the National Academy of Sciences (PNAS), which found that the trend toward increased dryness was easily reversible if global warming is kept below 1.5°C.

Regions characterized by Mediterranean climates include California, central Chile and the Mediterranean region itself. These regions rely heavily on winter rainfall to supply them through hot, dry summers.

Previous modeling and observational studies have shown that most Mediterranean climates experience less rainfall with global warming, with California being a notable exception.

But until now little was known about how increases in greenhouse gas emissions affect these climates.

The study, led by the University of Reading alongside the National Research Council of Italy (CNR-ISAC, Bologna) and Imperial College London, carried out modeling simulations showing how rises in emissions affect the Mediterranean and central Chile. The models showed that as greenhouse gases rise, rainfall levels decline rapidly, even within just a few years.

Dr Paulo Ceppi, from Imperial College’s Grantham Research Institute, said, “Our result implies that water resources in these regions would almost immediately benefit from stabilizing greenhouse gas concentrations, since this would interrupt the rapid decrease in rainfall. In other words, climate action is positive not only in the long-term, but also after just a few years.”

Although the same rapid decrease in rainfall was not seen in California, the simulations showed the region would still benefit in the long-term from stabilized emissions which would result in a steady increase in rainfall for the region.

The reason California responds in a different way to other Mediterranean regions to global warming is due to its proximity to the ocean, say the researchers.

Dr Ceppi said, “The warming of the ocean surface is not uniform, with some regions warming faster than others… Those areas of the ocean that warm faster than average cause remote changes in atmospheric winds that make Mediterranean regions drier. By contrast, other ocean areas that warm more slowly tend to make California wetter, while having little impact on rainfall in other Mediterranean regions.”

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