by It’s like the rivers of our planet the arteries of our planet. They are entwined around the globe in complex networks, carrying fresh water that sustains life around the world. Not only are rivers our lifelines, providing the drinking water we need to survive, but their fresh water reserves are also the main lifelines for 10 percent of all known animals and half of all known fish species, helping to sustain healthy and diverse ecosystems. . In short, they are our most renewable, affordable and sustainable freshwater storage houses.
However, people have surprisingly limited understanding of how much water the Earth’s rivers hold and how fast that water moves—two aspects that are critical to managing our planet’s precious fresh water resource.
Cedric Davida scientist at NASA’s Jet Propulsion Laboratory (JPL) in California compares the situation to spending money from a checking account without knowing the balance.
Related: NASA’s SWOT satellite maps of nearly all of Earth’s water (video)
“It’s like we had some idea of how much we were making and how much we were spending, but we didn’t know how much was in the account,” he told Space.com.
Much of the current literature around rivers refers to 50-year-old estimates made by the Russian Academy of Sciences, set out in a report published in Russian in 1974 that was later translated into English in 1978. This is probably difficult because it was difficult to collect updated estimates. especially when it comes to rivers that are far from human population. Even satellites It is impossible to notice how much water flows into some rivers from the ground, called run-off, which is the water resulting from the rain left on the surface of the planet that exceeds the absorption capacity of the ground. That excess water then flows into nearby bodies of water, including rivers.
Determining river speeds is also difficult based on traditional “back of the envelope” formulas based on in-situ measurements from 50 years ago, David told Space.com. In late April, David and his team did NASA the researchers sought the best estimates yet of the amount of water flowing through the Earth’s rivers, the rates at which it flows into the oceans and the extent to which both figures have changed. time.
“We are able to look at some good old numbers with some tricks that we didn’t even know were possible,” said David. “We did what we could to fix everything we could based on the limited observations we have.”
By using previous satellite data to model river runoff levels on a map, the researchers found that from 1980 to 2009, the total volume of water in the Earth’s rivers was 539 cubic miles (2,246 km cubic) on average, that’s about half. of the water volume of Lake Michigan. The Amazon Basin, which stretches from the Andes Mountains in Peru to the Atlantic coast of Brazil, holds 38 percent of all the Earth’s water, according to the study, published last month in Nature Geoscience. That same basin dumps the most water into the ocean—about 1,629 cubic miles (6,789 cubic kilometers) per year, or 18 percent of the total release to the ocean worldwide.
“I was hoping to show myself that there is much more river water than we thought,” said David. “It turned out, that’s not what we got – that’s a bit sobering.”
The new dataset, which covers 30 percent of the planet, consists of in-situ measurements and computer models representing nearly 3 million river segments worldwide. It also highlights rivers that have been depleted due to human overuse. Climate changeIrrigation projects and other landscape-modifying activities are likely to affect water supplies in numerous rivers, including the Colorado basin in the United States, the Amazon basin in South America, the Murray-Darling basin in Australia and the Orange River basin in southern Africa . .
“We’re trying to give people data to make smart decisions and start some conversations,” David said. To help with that goal, the new dataset and study are open access, meaning it’s free for anyone to read online. “We hope it would make a bit of a difference,” he said.
He also noted the value of open science in contributing to interesting scientific research as a whole.
The work that led to the new paper began in early 2022, when the study’s lead author, Elyssa Collins, came across publicly available code for a climate model that David had shared online. After a few months of tinkering with the code, Collins, now a doctoral student at North Carolina State University in Raleigh, contacted David with a few ideas, an entrepreneurial endeavor that led to a six-month internship under David at the JPL site . in Pasadena, California. “This is just one of many success stories [of open science] — if you give things away for free cool things happen,” David said.
In the coming years, the researchers plan to compare their latest estimates, based on computer models, with upcoming satellite data from NASA’s Surface Water and Ocean Topography, or SWOT, mission to estimate human footprints. on improving our planet’s water cycle.
“You can think of it as camera images but they tell you the rise of water,” David said of the SWOT data. The satellite, which has been mapping the height of water surfaces on Earth since December 2022, is helping scientists calculate the changes in river height, from which they estimate the amount of water present and released. Last month, the satellite took a depth of a temporary, shallow lake which grew for several weeks at the base of Death Valley National Park, which straddles the border of California and Nevada and is the warmest place on World. The 1-foot-deep (0.3-metre-deep) lake, known as Loch Manly, is spread over a larger area than expected for such a body of water due to strong winds, allowing for a SWOT study of events in a non-permanent, dedicated region. instruments.
Other early results show that SWOT water height data can fill gaps in the literature under changing conditions during and after floodsthat only flooded areas can’t be image captured and enhanced by satellites flood forecast.
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In addition to SWOT, above 30 NASA satellites currently records data about the Earth’s land surface, ice, oceans and atmosphere. They are there as part of an effort that the agency started in the 1980s, an effort dedicated to collecting the data needed to understand and predict the weather, of course, but also to monitor cyclones, floods, wildfires and other terrible changes on the planet. a climate made worse by human activities such as burning coal. Offering us a view of Earth on scales that could never be achieved on the ground, these satellites are helping scientists keep track of animals at risk of habitat lossSearch for signs of possible volcanic eruptionsdecode the changing chemistry of coastal waters and track rates of declining sea ice.
“It is rather underappreciated how much Earth science we do at NASA,” said David Space.com. In fact, half of the science done at JPL is Earth science, he said.
“We don’t have a Planet B – it’s been a long time.”
