It takes a long time for rock to be weathered into soil around the Mediterranean Sea, but only a few moments for that soil to be washed away in a rainstorm. The typical time for such storms is autumn - soon after summer, when fires often rob the topsoil of its protective plants. The landscape, so much loved by tourists as well as by local people, is in danger.
This is why experts from 44 universities in the EU are studying how to save it. The study, called Medalus (Mediterranean Desertification and Land Use), is on behalf of the European Commission.
The classic work on desertification, Desertification: Exploding the Myth by Professor David Thomas and NJ Middleton (1994, John Wiley & Sons), shows that in Europe, 86 million hectares - 28.6 per cent of susceptible drylands - have been at least moderately degraded by human activity. This is the highest percentage of any continent, beating even Africa (with only 15.6 per cent), and a larger area than has been affected in North America (covering 79.4 million hectares).
Much of Europe's damage is round the Black Sea and in Hungary. But a map in Thomas and Middleton's book shows the islands of Sardinia, Sicily and Crete to be badly degraded, and most of Spain and the southern half of Portugal degraded to some degree. Millions of people are affected.
Erosion of the European Mediterranean's hill slopes has been reduced by terracing, but encouraged by such activities as tree-felling for shipbuilding in previous centuries. Portugal's Alentejo region was devastated by a wheat-growing campaignfrom the 1930s to the 1960s: the aim was to be self-sufficient in the crop, but it had a low yield through lack of water, and exposed the soil to the sun.
The plants which do keep the Mediterranean soil in place have to be tough: growth more or less ceases when the soil dries out around the end of May.
Moisture may become scarcer as a result of global warming (though computer models offer conflicting answers). If so, the hardest hit will be the plants struggling to exist in the driest areas. Moreover, a higher proportion of rainfall is likely to come in violent, local autumn storms.
All this is happening in a farming environment which has changed. Upland farming has retreated. More pine trees are being planted, to check hillside erosion - but they take up water and offer a greater fire risk.
Farmers have left for the towns or for Australia, or else are growing "thirsty" crops such as oranges, lemons, lettuces and tomatoes on irrigated lowland. "These sell like crazy," says Professor John Thornes of King's College London, co-ordinator of Medalus. The warmth and sunlight make it possible to grow two or even three vegetable crops annually. But there is a price: in Spain, farming consumes 60 per cent of the water supply, while humans take just 10 per cent.
So demand for water for growers, as well as for tourists, has risen. Dr Nichola Geeson, one of Medalus's project managers, points out that growers use water sparingly, by installing drip irrigation and growing crops under polythene. Nevertheless the agriculture which puts cheap Spanish lettuces and strawberries in British supermarkets is not sustainable. Water from underground is being pumped up near the coast and is not being replenished by rainfall. As a result, salt water flows in. In 1994, when Dr Geeson ordered tea in a southern Spanish hotel, she found it almost undrinkable because of the water's saltiness. At the height of the season, water for tourists has to be shipped in by tanker.
Professor Thornes, who has worked in Spain for 30 years, is keen that Medalus should look at real situations and how real people are farming in them. In its first phase it looked in detail at individual hill slopes in Portugal, France, Spain, Sardinia and Greece. In its second phase, it added some river valleys.
A third phase is studying how to define what makes an area sensitive, such as the Alentejo or the Greek island of Lesbos. Stan Openshaw, at Leeds University, and Francisco Lopez-Bermudez of Murcia University are looking at the economic and social aspects of land degradation. This third phase is also studying the normally dry channels which carry water after heavy rain.
The conference, in much-degraded Crete, brings together economists, scientists and officials whose policies affect the Mediterranean to discuss the Medalus findings to date. They will make a field trip to see problems and possible solutions.
Professor Thornes thinks that the European set-aside policy for taking land out of cultivation has helped the Mediterranean, but EU subsidies for planting eucalyptus - a fast-growing timber crop - and land clearance have not. He believes that allowing the natural vegetation to grow is a better policy for abandoned farmland than covering it with eucalyptus and pine. Tree plantations take up soil moisture, and it is expensive to get the trees to survive. Tourist use of abandoned land - often for golf courses, increasing water demand - also increases the risk of fire.
He also points out the need for better policies on the use and pricing of scarce water. Growers can always produce more vegetables with more water; but when a dry year comes, they tend to abandon land they just cleared. Water for south-east Spain can be brought from the westward-flowing river Tagus, but the cost is high.
Antonio de la Morena of the Spanish Tourist Office argues that it is up to governments to provide water through taxation, and points out that Spain is one of the world's richest countries in terms of reservoirs. But if governments spend huge amounts on water, people may have to forgo other services. It is a tricky equation - and meanwhile, the land is getting drier.