"Desertification is a slow-moving process and once we realise it is happening it will be too late to go back," Kosmas told Reuters in an interview.

Desertification is being fuelled by a reduction in average rainfall coupled with higher temperatures, deforestation and human activities such as farming, construction and tourism. Kosmas said long-term environmental changes meant all countries across the Mediterranean basin would eventually be affected -- and that populations would drift to cooler north European latitudes.

"Desertification means that people cannot earn a living off the land so they move. They become migrants, flocking to urban areas," he said.

"Northern European countries have accepted this, though we (in the region) need to start taking specific measures immediately because we have done little until now."

Greece, which is the committee's main focus, has been experiencing one of its worst droughts in 20 years and its landscape will change substantially within the next decade, Kosmas said.

Greece's average rainfall has fallen by about 30 percent since the mid 1970s, and last January was the driest in half a century.

"About 34 or 35 percent of the country has been highlighted by us as extreme danger areas that face desertification, with great repercussions for humans and the economy," Kosmas said.

Parts of the southern Peloponnese region, many of the Aegean islands popular with tourists, as well as northern, central Greece and the wider Athens region are at high risk.

Greece, one of the fastest growing economies in the euro zone, is experiencing a construction boom and a sharp rise in tourism that has strained natural resources.

Tens of thousands of holiday homes are being built this year alone to meet the demand from foreigners, and the construction industry has been growing by a third every year since 2000.

But Kosmas said the economic benefits could soon be outweighed by long-term environmental damage.