

The volume of fresh water pouring from the world’s rivers has risen rapidly since 1994, in what researchers say is further evidence of global warming. The study, led by a team at UC Irvine, is the first to estimate global fresh-water flow into the world’s oceans using observations from new satellite technology rather than through computer or hydrological models.

Published this week in the Proceedings of the National Academy of Sciences, the study found that annual fresh-water flow increased 18% from 1994 to 2006, suggesting an acceleration in the global water cycle of evaporation and rainfall, which influences the intensity of storms, floods and droughts.

UC Irvine Earth System Science professor Jay Famiglietti, the principal investigator, said that the data have major implications for California, where warmer temperatures are already triggering earlier snow melt. Rising sea levels are expected to significantly alter the state’s long coastline.

“Until now, we have had no continuous record of global-scale river discharge,” said Famiglietti. He noted that the time period of the study was short, but added, "If these trends persist, they will be a smoking gun that the water cycle intensification, predicted by climate scientists, is already upon us."

Globally, river flows are often a politically-fraught subject. Countries measure the quantity of water locally, and inconsistently, with mechanical or electronic guages, but they often refuse to share the data, according to hydrologist Peter Gleick, editor of the biannual "World's Water" survey and director of the Oakland-based Pacific Institute think tank. Pakistan and India are in conflict over flows from the Indus. Israelis, Palestinians and Lebanese all depend on the Jordan River. Ten countries are sharing water along the Nile.

The UC Irvine study “is additional clear evidence that the hydrological cycle is accelerating,” Gleick said. "This is exactly what climate modelers have said would happen from climate change, and now we see it happening. How much more evidence do we need before we take action against climate change?”