With the Prairies likely to face a severe drought within the next couple of decades, Alberta should limit the number of people who move there, warns a report by two Canadian water experts.

David Schindler, an ecology professor at the University of Alberta, says future droughts will likely be far worse than the ones that turned the Prairies into a dust bowl in the 1930s.

He says Alberta's booming economy and rapid growth have made it the province vulnerable to water shortages.

Schindler co-authored the study with W.F. Donahue. It was published online Monday in the Proceedings of the National Academy of Sciences.

The authors say water levels in some rivers in Alberta have declined by 20 to 84 per cent in the past 100 years.

The biggest declines were measured in rivers and lakes in the central and southern part of the province, where Albertans draw most of their water.

But Schindler says his findings show the Northwest Territories, Saskatchewan and Manitoba are also vulnerable to drought.

Alberta's Environment Minister Guy Boutilier says people in the province will have to reduce their use of water by a third within the next seven years.

Boutilier predicts that if people don't do that, it could lead to disputes among Prairie provinces as the resource dries up.

Schindler's study says evidence suggests the 20th century's relatively moist conditions were a fluke and the past 2,000 years have generally been drier. He says previous dry periods occurred several times a century, and usually lasted for several decades.

He predicts that if the climate reverts back to drier conditions and global warming continues, parts of the Prairies that are already dry will probably begin to experience the near-desert conditions seen in parts of the U.S. West.