Thailand ? Desertification represents one of the “greatest environmental challenge of our times” and could set off mass migrations of people fleeing degraded homelands, a United Nations report warned today.

The report called on governments in arid regions to revise rules on land use to halt overgrazing and unsustainable irrigation practices. It also urged better coordinated policies to address the problem of desertification.

“It is imperative that effective policies and sustainable agricultural practices be put in place to reverse the decline of drylands,” says Hans van Ginkel, a professor at the United Nations University, which produced the report.

The report said about 2 billion people, a third of the Earth’s population, are potential victims of desertification, which is defined as land degraded by human activities like farming and grazing.

If the problem is left unchecked, some 50 million people could be forced from their homes over the next decade, the report said.