But the river system that covers two-thirds of Australia's irrigated farming land is also suffering from decades of overuse.

ECONOMIST: To turn a drought into wine

Commercial irrigated farming has bright prospects.

ECONOMIST: Brazil

Irrigated rice-farming, which is two or three times more productive than the rain-fed sort, is growing rapidly throughout the basin, albeit from a low base.

ECONOMIST: The Mekong river

Weiss believes this climate change initiated a mass migration away from dry-land farming to the creation of irrigated fields along the Tigris and Euphrates rivers, allowing the people to build some of the earliest institutions of civilization.

CNN: Past may hold clues to climate's future