Satellites weigh Africa's water

The volume of water lost from the land amounts to 334 cubic km, which is almost as much as all Africans have consumed over the period.

The data comes from Nasa spacecraft that can detect changes in gravity caused by water as it cycles between the sea, the atmosphere and the land.

Experts stress no firm conclusions should be drawn from the short study.

Professor Jay Famiglietti from the University of California-Irvine said much longer times series were needed to detect real trends and any signal that might indicate a significant shift in climate.

"There are natural climate variations, the natural ups and downs," he explained.

"Another big factor is human control of the water cycle - reservoir management, the storage of water on continents.

"Groundwater mining leads to heavy depletions of water. Wetland drainage, river diversion projects - all of those factors contribute to these storage variations that we see and we'll be working on trying to sort those out over the next few years," he told the BBC.

from the BBC