Scientists say they've used satellite data to measure for the first time the amount of water that rises and falls in the Amazon River floodplain each year.

Ohio State University researchers say the information is critical to predicting floods and droughts that might be brought about by global climate change, a university release said Friday.

Until now, researchers trying to estimate the amount of water in the Amazon floodplain and other river systems around the world had only a few sporadic field studies and crude assumptions to go on, the release said.

"Nobody knows exactly how much water there is on the planet," Doug Alsdorf, OSU associate professor of earth sciences, said. "We need to understand how our water supply will change as the climate changes, and the first step is getting a handle on how much water we actually have."

"Satellite observations are the only reliable option for places like the Amazon and especially the Congo Basin, where in-person measurements are near-impossible," he said.

"Just getting there is a serious challenge."

In the rainy season, water flows into various locations on the Amazon floodplain at a rate of 190,000 cubic feet per second, and during the dry season, it drains away into the Amazon River -- and, ultimately, into the Atlantic Ocean -- at a rate of 265,000 cubic feet per second, the researchers said.

The findings are a start in revealing data about the many unknowns scientists must deal with as they work to understand climate change, Alsdorf said.