Desert Cities Are Living on Borrowed Time, UN Warns

The 500 million people who live in the world's desert regions can expect to find life increasingly unbearable as already high temperatures soar and the available water is used up or turns salty, according to the United Nations.

Desert cities in the US and Middle East, such as Phoenix and Riyadh, may be living on borrowed time as water tables drop and supplies become undrinkable, says a report coinciding with today's world environment day.

Twentieth-century modernist dreams of greening deserts by diverting rivers and mining underground water are wholly unrealistic, it warns.

But the report also proposes that deserts become the powerhouses of the next century, capturing the world's solar energy and potentially exporting electricity across continents. For instance, a 310-square mile area of the Sahara could, with today's technology, generate enough electricity for the whole world.

The problem now facing many communities on the fringes of deserts, says the UN environment programme report, is not the physical growth of deserts but that rising water tables beneath irrigated soils are leading to more salinisation - a phenomenon already taking place across large tracts of China, India, Pakistan and Australia. The Tarm river basin in China, it says, has lost more than 5,000 square miles of farmland to salinisation in a period of 30 years.

The report suggests that Middle Eastern countries such as Saudi Arabia have used water from the desert very unwisely. Rather than growing staple crops such as wheat or tomatoes, it suggests that precious water should be used only for high value crops such as dates and fish farming.

The mining "fossil" water, laid down many millions of years ago, was once believed to have the potential to green deserts, but is now not thought to be a solution - except in Libya, where opinion is divided as to whether supplies may last 100 or 500 years.

But the greatest threat to people and wildlife living anywhere near deserts is climate change, which is already having a greater impact on desert regions than elsewhere. The Dashti Kbir desert in Iran has seen a 16% drop in rainfall in the past 25 years, the Kalahari a 12% decline and Chile's Atacama desert an 8% drop.

Most deserts, says the report, will see temperatures rise by 5-7C by the end of the century and rainfall drop 10-20%. This will greatly increase evaporation and dust storms, and will move deserts closer to communities living on their edges.

The problems of more heat and lower rainfall are being compounded by the melting of glaciers in mountainous regions. These waters sustain life in deserts but would be perilously close to drying up if global warming continued as expected.

The glaciers in the mountains of south Asia are expected to decline by 40% to 80% in the next century with profound effects on large populations in Bangladesh, Pakistan, India and China.

Much of the water used for farming the south-west US, central Asia and around the Andes is drawn from rivers that originate in snow-covered mountains, says the report.

Development in the next 100 years is largely contingent on what happens to the climate. However, the report envisages that deserts will become more popular tourist destinations and that some of the plants that grow there could be "crops of the future".

"Deserts are threatened as never before by climate change, overexploitation of water and salinisation," said Professor Andrew Warren of University College London, one of the report's authors.

"We risk losing not only astounding landscapes and ancient cultures but also wild species that may hold keys to our survival."