US satellites have detected a large loss of fresh water reserves in the Tigris and Euphrates river basins during a seven-year period beginning in 2003, a new study has found.

The river basins, which water parts of Iraq, Iran, Turkey and Syria, have lost almost as much water as is in the Dead Sea, the study found.

"That's enough water to meet the needs of tens of millions to more than a hundred million people in the region each year, depending on regional water use standards and availability," said Jay Famiglietti, the lead investigator.

The study, which is to be published Friday in the journal Water Resources Research, was conducted by scientists at the University of California at Irvine, NASA's Goddard Space Flight Center and the National Center for Atmospheric Research.

It relies on data gathered over a seven year period by NASA's GRACE satellites, which track global changes in water reserves.

Because changes in water reserves affect the Earth's mass within a given region, the satellites measure gravity locally to tease out those changes.

"GRACE data show an alarming rate of decrease in total water storage in the Tigris and Euphrates river basins, which currently have the second fastest rate of groundwater storage loss on Earth, after India," said Famiglietti, a hydrologist at UC Irvine.

Part of the loss was attributed to a 2007 drought that dried out soil and shrank snowpacks, and another part to the loss of surface water from lakes.

But most of it -- about 60 percent -- was traced to the pumping of groundwater, which typically increases during and after a drought.

Famiglietti noted, as an example, that Iraq drilled about 1,000 wells in response to the 2007 drought.

"The rate (of loss) was especially striking after the 2007 drought. Meanwhile, demand for freshwater continues to rise, and the region does not coordinate its water management because of different interpretations of international laws," he said.