Shuttle Radar Topography Mission. Artwork Courtesy: Ball Aerospace & Technologies Corp.
The Amazon is the largest drainage basin in the world. And for the first time – thanks to satellites — scientists have been able to measure the amount of water that rises and falls annually in the Amazon River floodplain.
An international squadron of spacecraft — three NASA satellites and one from the Japan Aerospace Exploration Agency (JAXA) – were used to get the first direct measure of water in the floodplain.
The results stemming from the satellite measurements: 285 billion metric tons, or 285 cubic kilometers of water by volume – an amount that’s over half the volume of Lake Erie, which is the world’s 15th largest lake.
Doug Alsdorf, associate professor of earth sciences at Ohio State University, and his colleagues report that, until now, researchers could only estimate the amount of water in the Amazon floodplain using a few sporadic field studies and crude assumptions about water flow.
In fact, water volumes on any floodplain are poorly known, if at all. Yet this information is critical to predicting the floods and droughts that could accompany global climate change, Alsdorf says.
“Nobody knows exactly how much water there is on the planet,” Alsdorf adds. “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.”
Observations haven’t been made before
Alsdorf and his associates combined data from the Gravity Recovery and Climate Experiment, the Global Precipitation Climatology Project, the Shuttle Radar Topography Mission, and the Japanese Earth Resources Satellite. They focused on measuring water level changes during the wet and dry seasons between 2003 and 2006.
Taken together, these satellites gave a picture of how the Amazon landscape changed as highland rains surged through the river’s many tributaries and the resulting overflow spilled into the lowland jungle. After the water receded, the research team calculated the change in volume along the floodplain.
These observations haven’t been made before, in part due to the immense difficulty of combining different kinds of data in a reliable way. The researchers had to meld gravity readings — a measure of the flood water’s mass — with radar and optical measurements of the water level and extent of the floodplain.
The floodplain total, however large, represents only 5 percent of the amount that scientists believe is emptying from the Amazon River into the ocean every year.
Alsdorf says that the new finding begs the question of exactly how much water is flowing through the Amazon system. In fact, the satellite data underscores the many unknowns that scientists must confront as they work to understand climate change.
The Amazon, however grand in size, is just one river basin among countless basins around the planet — each vital to the soil quality and water quality of its surroundings, Alsdorf emphasizes.
Future measurements should be easier with the future launch of NASA’s Surface Water and Ocean Topography (SWOT) mission in 2020.
By LD/CSE