LONDON, June 4 (Xinhua) -- The world's deserts are facing serious challenges as a result of global climate change, increasing water demands, tourism and salt contamination of irrigated soils, according to a report to be published by the UN Environment Program (UNEP) on Monday.

Geography professor of London College Andrew Warren warned at the study's launch in London that the unique landscapes, ancient cultures, flora and fauna in deserts were at risk of disappearing.

"What alarms me now is that they are threatened as never before by climate change, by over-exploitation of groundwater, salinization and the extinction of wildlife," he said.

The 187-paged report, named "The Global Deserts Outlook", is the first thematic report among "The Global Environment Outlook (GEO)" series of environmental assessments by the UNEP. Its launch coincided with the World Environment Day on Monday.

The GEO report, prepared by experts from all over the world, traces the history and astonishing biology of the deserts and assesses likely future changes in deserts, the UNEP spokesman Nick Nuttall told reporters at the same event.

Almost one-quarter of the earth's land surface - some 33.7 million square kilometers - has been defined as "desert" in some sense, and is inhabited by over 500 million people, according to the report.

The study outlines that there has been an overall temperature increase in desert regions of between 0.5 and two degrees Celsius between 1976 and 2000, compared to an overall rise in world temperatures of 0.45 degrees Celsius.

Hotter temperatures mean that glaciers are receding, with less water to sustain deserts. Most of the 12 desert regions, whose future climate has been modeled, are facing a drier future with rainfall forecast to be 10 to 20 percent lower by the end of the century.

Increasingly dry rivers, inefficient water use such as irrigation, and population growth will all add to water shortages in deserts, the report said. Countries like Saudi Arabia, Pakistan, western China, Chad, Iraq, Niger and Syria will be particularly affected.

Desert wetlands are probably the most threatened ecosystems, asa result of their valuable water supplies being diverted to domestic or agricultural use. Semi-arid rangelands are more likely to turn into deserts, the report said.

Most deserts' groundwater levels were dropping "very, very quickly" as ancient underground aquifers became exhausted, Warren told reporters.

Meanwhile, road-building, pollution and hunting were threatening flora and fauna in the deserts while rising water tables and irrigation were causing the salinization of soils and groundwater, he added.

UNEP spokesman Nuttall told reporters that the report was designed to challenge the idea that deserts were "seas of sands that are unchanging, indomitable".

Instead, it was an "early warning" of the current and future problems that deserts and the world were facing, and the need to find a solution, he said.

However, the report pointed out that if carefully treated, deserts can provide answers to many challenges that human beings are facing as well, such as energy, food and medicine.

Deserts could become the "carbon-free powerhouses of the 21st century", the report noted, harnessing the wind and sun.

Most deserts having sunlight and temperature regimes are prime locations for shrimp and fish farms in locations like Arizona to the Negev desert in Israel and the source of novel drugs, herbal medicines and industrial products derived from the plants and animals adapted to these arid areas.

And if the huge, solar-power potential of deserts can be economically harnessed, the world has a future free from fossil fuels, the report forecast.

Tourism based around desert nature can, if sensitively managed,deliver new prospects and perspectives for people in some of the poorest parts of the world, report also suggested. Enditem