The rivers of our planet are like the arteries of our planet. They are woven across the globe in complex networks, transporting vital fresh water across the globe. Rivers are not only our own lifelines, providing us with the clean water we need to survive, but their freshwater reserves are also the primary lifelines for 10% of all known animals and the half of all known fish species, helping to maintain healthy and diverse ecosystems. . In short, they are the most renewable, accessible and therefore sustainable freshwater reservoirs we have.
Yet humans have a surprisingly limited understanding of how much water Earth’s rivers contain and how fast that water moves—both of which are essential to managing our planet’s precious freshwater resources.
Cedric Davida scientist at NASA’s Jet Propulsion Laboratory (JPL) in California, compares the situation to spending money in a checking account without knowing the balance.
Related: NASA’s SWOT satellite maps almost all of Earth’s water (video)
“It’s like we had an 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 on rivers refers to 50-year-old estimates by the Russian Academy of Sciences, described in a 1974 report published in Russian and later translated into English in 1978. This is probably due to the fact that updated estimates have been difficult to gather, particularly when it comes to rivers far from human populations. Even satellites We cannot observe the amount of water from the earth that flows into certain rivers, called runoff, that is, water resulting from precipitation remaining on the surface of the planet that exceeds the capacity of absorption of the earth. This excess water then flows to neighboring bodies of water, particularly rivers.
River velocities are also difficult to determine based on conventional “backwards” formulas based on in situ measurements from 50 years ago, David told Space.com. At the end of April, David and a team of NASA Researchers have embarked on a quest to provide the best estimates yet of how much water flows in Earth’s rivers, how fast it flows into the oceans, and the evolution of these two figures over time. time.
“We’re able to revisit some good old acts with a few tricks that even we didn’t know were possible,” David said. “We have done what we can to repair everything we can based on the limited observations we have.”
Using previous satellite data to model runoff levels associated with rivers on a map, researchers found that, from 1980 to 2009, the total volume of water in Earth’s rivers averaged 539 cubic miles (2 246 cubic kilometers), or about half. of the water volume of Lake Michigan. The Amazon River basin, which stretches from the Andes in Peru to Brazil’s Atlantic coast, contains 38 percent of all Earth’s water, according to the study, which was published last month in Nature Geoscience. This same basin also discharges the largest amount of water into the ocean – approximately 1,629 cubic miles (6,789 cubic kilometers) per year, or 18% of the total discharge into the world ocean.
“I was hoping to demonstrate to myself that there is a lot more water in the rivers than we thought,” David explained. “Turns out that’s not what we got – that’s a bit sobering.”
The new dataset, which covers 30% of the planet, consists of in situ measurements and computer models representing nearly 3 million river segments worldwide. It also highlights rivers that have become depleted due to overexploitation by humans. Climate changeirrigation projects and other landscape modification actions likely affect the water supply of several rivers, including the Colorado River 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 provide data that allows people to make intelligent decisions and start conversations,” David said. To achieve this goal, the new dataset and study are open access, meaning anyone can read them online for free. “We hope it makes a little difference,” he said.
He also highlighted the value of open science in facilitating interesting scientific research overall.
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 code, Collins, now a doctoral student at North Carolina State University in Raleigh, contacted David with some ideas, an enterprising effort that resulted in a six-month internship under David at JPL. in Pasadena, California. “This is just one of the many successes (of open science): if you give things away for free, interesting things happen,” David said. “It’s so important that we learn from each other, that we share, and that we include everyone who cares about the science that we do.”
In the coming years, the researchers plan to compare their latest estimates, based on computer models, to upcoming satellite data from NASA’s Surface Water and Ocean Topography, or SWOT, mission to improve the footprint estimates. human impact on our planet’s water cycle.
“You can think of them as camera images, but they just tell you the elevation of the water,” David said of SWOT data. The satellite, which has been mapping the heights of bodies of water on Earth since December 2022, helps scientists calculate changes in river height, from which they estimate the amount of water present and released. Last month, the satellite captured the depth of a temporary, shallow lake which grew for several weeks at the foot of Death Valley National Park, which spans the California-Nevada border and is the hottest place on earth. Earth. The foot-deep (0.3 meter) lake, nicknamed Manly Lake, extends over a larger area than expected for such a body of water due to strong winds, allowing SWOT to study events in a region without a permanent and dedicated environment. instruments.
Other initial results show that SWOT water height data can also fill gaps in the literature on changing conditions. during and after floodsthat satellites that generally only image flooded areas generally cannot capture, and improve flood forecast.
In addition to SWOT, more 30 NASA satellites currently record data on the Earth’s land surface, ice, oceans and atmosphere. They’re there as part of an effort started by the agency in the 1980s, an effort to glean the data needed to understand and predict the weather, of course, but also to monitor cyclones, floods, fires forests and other devastating changes on the planet. climate exacerbated by human activities such as coal burning. By giving us a view of Earth on scales that could never be obtained on the ground, these satellites help scientists keep tabs on animals vulnerable to habitat lossTo research signs of potential volcanic eruptionsdecode the alteration of coastal water chemistry and monitor the rates of sea ice decline.
“It’s relatively underappreciated how much we do in Earth science at NASA,” David told Space.com. In fact, half of all science done at JPL is in Earth sciences, he said.
“We don’t have a planet B, it’s been a long time.”