How much of the Earth is actually covered by rivers and streams? A lot more than previously thought, according to a study published in Science. Satellite images reveal the Earth’s rivers and streams cover 45 percent more surface area traversing about 773,000 square kilometers (300,000 square miles) around the globe – and it could have major implications in how we understand climate change.
Rivers and streams are a major source of greenhouse gas emissions, making up as much as five times more than the world’s lakes and reservoirs combined. Organic matter in the soil and vegetation is converted by microbes living in the waterways, generating greenhouse gases like carbon dioxide and methane, which is 25 times more potent than carbon dioxide. A greater number of river and stream surface area means more contact between water and air and a greater rate of carbon exchange with the atmosphere, especially when humans pollute the waterways; more greenhouse gases are released when pollutants like fertilizers and sewage make their way to water systems.
The study implies that interactions between rivers and the atmosphere are likely greater than previously thought, and estimates for greenhouse gas emissions are probably higher than previously accounted for.
"As we try to mitigate the effects of climate change, it's really important that we clearly understand where the carbon that we are emitting goes, and that requires us to accurately quantify the global carbon cycle," said senior author Tamlin Pavelsky in a statement. "Our new calculation helps scientists better assess how much carbon dioxide is moving from rivers and streams into the atmosphere each year."
These findings can be particularly pronounced in the Arctic, where impacts of climate change on carbon fluxes are a major concern.
Researchers went beyond previous research based mostly on theoretical extrapolations of small amounts of actual data. This time around, they analyzed thousands of satellite images from NASA, paired it with 58 million on-the-ground measurements from the US Geological Survey and Water Survey of Canada. From there, the team used statistical modeling that measured from the smallest streams to the world’s largest rivers to estimate river and stream coverage worldwide.