NASA Scientists Complete 1st Global Survey of Freshwater Fluctuation

From NASA

Mar 3, 2021

To investigate humans’ impact on freshwater resources, scientists have now conducted the first global accounting of fluctuating water levels in Earth’s lakes and reservoirs – including ones previously too small to measure from space. 

The research, published March 3 in the journal Nature, relied on NASA’s Ice, Cloud and land Elevation Satellite 2 (ICESat-2), launched in September 2018. 

ICESat-2 sends 10,000 laser light pulses every second down to Earth. When reflected back to the satellite, those pulses deliver high-precision surface height measurements every 28 inches (70 centimeters) along the satellite’s orbit. With these trillions of data points, scientists can distinguish more features of Earth’s surface, like small lakes and ponds, and track them over time.

Scientists used these height measurements to study 227,386 water bodies over 22 months and discovered that, from season to season, the water level in Earth’s lakes and ponds fluctuates on average by about 8.6 inches (0.22 m). At the same time, the water level of human-managed reservoirs fluctuate on average by nearly quadruple that amount – about 34 inches (0.86 m).

While natural lakes and ponds outnumber human-managed reservoirs by more than 24 to 1 in their study, scientists calculated that reservoirs made up 57% of the total global variability of water storage.

To investigate humans’ impact on freshwater resources, scientists have now conducted the first global accounting of fluctuating water levels in Earth’s lakes and reservoirs – including ones previously too small to measure from space.Credits: NASA’s Goddard Space Flight Center/Scientific Visualization Studio

Download this video in HD formats from NASA Goddard’s Scientific Visualization Studio

“Understanding that variability and finding patterns in water management really shows how much we are altering the global hydrological cycle,” said Sarah Cooley, a remote sensing hydrologist at Stanford University in California, who led the research. “The impact of humans on water storage is much higher than we were anticipating.” 

In natural lakes and ponds, water levels typically vary with the seasons, filling up during rainy periods and draining when it’s hot and dry. In reservoirs, however, managers influence that variation – often storing more water during rainy seasons and diverting it when it’s dry, which can exaggerate the natural seasonal variation, Cooley said. 

Cooley and her colleagues found regional patterns as well – reservoirs vary the most in the Middle East, southern Africa, and the western United States, while the natural variation in lakes and ponds is more pronounced in tropical areas.

The results set the stage for future investigations into how the relationship between human activity and climate alters the availability of freshwater. As growing populations place more demands on freshwater, and climate change alters the way water moves through the hydrological cycle, studies like this can illuminate how water is being managed, Cooley said.

“This kind of dataset will be so valuable for seeing how human management of water is changing in the future, and what areas are experiencing the greatest change, or experiencing threats to their water storage,” Cooley said. “This study provides us with a really valuable baseline of how humans are modulating the water cycle at the global scale.”

The researchers’ methods relied on a second satellite mission, as well – Landsat, the decades-long mission jointly overseen by NASA and the U.S. Geological Survey. The team used Landsat-derived, two-dimensional maps of bodies of water and their sizes, providing them with a comprehensive database of the world’s lakes, ponds, and reservoirs. Then, ICESat-2 added the third dimension – height of the water level, with an uncertainty of roughly 4 inches (10 cm). When those measurements are averaged over thousands of lakes and reservoirs, the uncertainty drops even more.

Although ICESat-2’s mission focuses on the frozen water of Earth’s cryosphere, creating data products of non-frozen water heights was also part of the original plan, according to Tom Neumann, ICESat-2 project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Now, with the satellite in orbit, scientists are detecting more smaller lakes and reservoirs than previously anticipated – in this study they detected ponds half the size of the Lincoln Memorial Reflecting Pool.

“We’re now able to measure all of these lakes and reservoirs with the same ‘ruler,’ over and over again,” Neumann said. “It’s a great example of another science application that these height measurements enable. It’s incredibly exciting to see what questions people are able to investigate with these datasets.”

For more information on ICESat-2, visit www.nasa.gov/icesat-2

Header image: Lake Mead, along the Colorado River. Credit: National Park Service


By Kate Ramsayer
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Last Updated: Mar 3, 2021Editor: Kate Ramsayer

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Steve Case
March 4, 2021 2:07 am

 “The impact of humans on water storage is much higher than we were anticipating.” 

Or “Worse than previously thought”

Will they ever put a cork in it?

Bryan A
Reply to  Steve Case
March 4, 2021 5:26 am

But fortunately hoomans only affect hooman engineered and constructed water reservoirs, AS THEY WERE INTENDED TO BE UTILIZED

Bill Powers
Reply to  Steve Case
March 4, 2021 10:54 am

Steve the answer is no. I and others have posted this Mencken quote often but it always bears repeating

“The whole aim of practical politics is to keep the populace alarmed — and hence clamorous to be led to safety — by menacing it with an ENDLESS series of hobgoblins, all of them imaginary.” 

We have a massive bureaucracy that was created out of whole clothe with private sector taxes to manufacture hobgoblins. Think of them, Federal, State and Local collectively as the Menace Machine or the Hobgoblin Haberdashery

WBrowning
Reply to  Bill Powers
March 8, 2021 6:27 am

They want to get rid of Hydro Power, yet they want everyone to drive an electric “lithium bomb” car. Makes perfect sense.

Ron Long
March 4, 2021 2:20 am

So first NASA releases the statement that the earth has undergone 10% greening this last 20 years alone, then they release the statement “…we are altering the global hydrological cycle.”

Seems like either NASA has become bi-polar or there are competing factions within NASA pushing a different agenda. It appears to me that the data for both sides appears to be good data, just the tone changes. Curiouser and curiouser (The Cat in the Hat? Dr. Seuss?).

Ken Irwin
Reply to  Ron Long
March 4, 2021 4:11 am

Curiouser and curiouser said Alice (in Wonderland)

fred250
March 4, 2021 2:33 am

I can’t see anything surprising about this at all.

Yes, humans control a lot of surface water.

How else do modern civilisations exist. !

….. and why is it a problem ?

And if this knowledge/data can help us use that water more efficiently, all the better.

Last edited 4 months ago by fred250
Bryan A
Reply to  fred250
March 4, 2021 5:29 am

Exactly, if hoomans weren’t here, those largely fluctuating water sources WOULDN’T EXIST

Clyde Spencer
Reply to  Bryan A
March 4, 2021 8:00 am

And the run-off would be flushed directly into the oceans, and ALL the lake-level variation would be ‘natural.’ What humans have done is to retard the run-off. The 57% variability statistic of anthropogenic water storage really seems to be a non sequitur. That is, what is the practical utility? Is it any more meaningful than counting the number of sand grains on a beach?

Larry in Texas
Reply to  fred250
March 4, 2021 1:40 pm

Having been an attorney for over twenty-six years representing a major municipal water utility in Texas, I consider the article referenced in Nature magazine to be a Captain Obvious moment. Duh, man-made reservoirs that have publicly available data already in place (see waterdatafortexss.org to understand what I mean) have shown this type and degree of variability for years. While it’s nice to have a little bit more precise data, especially for smaller natural bodies of water, this dataset’s value seems to be more like propaganda for the warmist agenda.

Their money would be better spent fixing the problems with their missing Arctic sea ice data compilation.

fred250
March 4, 2021 2:39 am

“Then, ICESat-2 added the third dimension – height of the water level, with an uncertainty of roughly 4 inches (10 cm)

.

And yet they can measure sea levels with huge waves and all…. to the nearest mm! 😉

MarkW
Reply to  fred250
March 4, 2021 7:38 am

I would take the claim that they can measure to within 4 inches with a pretty large grain of salt.

Lance Flake
Reply to  MarkW
March 4, 2021 7:56 am

A 4 inch grain

DMacKenzie
Reply to  fred250
March 4, 2021 7:50 am

Yeah 10 cm, but if you take a million readings, your average becomes accurate to a hundred of a cm. Every statistician knows the square root of N rule…./sarc
Well, other than the equipment is actually taking a few giga-readings per second already and statisticians don’t have a practical basis for where the non-random errors exist…./double/s

fred250
Reply to  DMacKenzie
March 4, 2021 10:34 am

Except the thing you are measuring could actually change while you were taking all those readings.

Thus totally discounting any √n rule.

Mike Dubrasich
Reply to  fred250
March 4, 2021 6:45 pm

We’ve been through this before, but it might bear repeating (see Munging The Sea Level Data by Willis Eschenbach here).

Repeated measurements improve precision but not accuracy. Precision increases by the reciprocal of the sq root of N because precision is the degree of agreement among repeated measurements.

Accuracy is the degree of agreement of a set of measurements with the true value of the quantity being measured. Measurement errors (aka systemic errors) can lead to bias (poor accuracy) if the mean of many separate measurements differs significantly from the true value.

Calibration can improve accuracy if the true value is known. Repeated measures cannot improve accuracy, only precision. That’s some stats for you, without sarcasm.

The Eschenbach essay noted that satellites which measure sea level use lakes as calibration surfaces. This post claims lake levels fluctuate. If both those contentions are true (I have no reason to doubt them), then the calibration lakes are not reliable as such. Inaccuracy (bias) overwhelms the sea level measurements, no matter how precise they might be.

Disputin
March 4, 2021 2:59 am

Fluctutions? No, fluctueulopeans!

Last edited 4 months ago by Disputin
tim maguire
March 4, 2021 4:11 am

I can see the value in using this measurement system for natural water sources, but I don’t see the relevance to the reservoirs. They’re not natural and they’ll go up and down based on forcings that are at best only partially related to the forcings that move natural water sources. I don’t see why it’s alarming (or even surprising) that they account for a disproportionate amount of variability of water levels. My reaction is, of course they do.

Larry in Texas
Reply to  tim maguire
March 4, 2021 1:45 pm

You got it, Tim. Perfectly interesting data that is relatively useless for most folks in the business of managing man-made reservoirs.

James Donald Bailey
March 4, 2021 4:12 am

What about flooding? Winter snow melt? It sure would be nice if natural water level only varied about half a foot.

And dry stream or river beds that fill up or even rage when there are rains?

Did they include the increase in water surface area?

As I watch the TVA vary the water level, a significant objective is to minimize flooding further down the river system. But watching the boat docks alternate between high and dry and almost under water, I am not surprised that man made lakes average three feet of variation in water levels.

But that is the nature of averaging one dimension. Something with rare massive variations averages away. Something with frequent large variations shows up in the average.

The next time you hear about a river that has risen a couple stories above normal and is overflowing its banks, don’t forget that is natural and only averages out to half a foot. But how dare those meanies controlling the dam store water for later release or use.

Ed Reid
Reply to  James Donald Bailey
March 4, 2021 4:41 am

The increase in water surface area might not always be detectable. B. Everett Jordan Lake in North Carolina is almost completely surrounded by evergreen trees at the waterline, so the area increase is largely obscured from above. Flood control demands periodically increase the water level by 10-15 feet, moving the water line several 10s of feet into the trees. Treating the lake as a “swimming pool”, each foot of increased water level equals ~1 billion gallons of water, but the actual increase in stored water volume is much larger.

James Donald Bailey
Reply to  Ed Reid
March 4, 2021 7:01 am

Since they are using lasers, they should be able to use it like LIDAR. Some rays get reflected by leaves, some get reflected by the ground. By processing the data, they can remove the trees. Archeologists are using it to find ruins in rainforests.

I am a little curious. Usually they make multiple passes at different locations, sort of like mowing or ploughing. And they are not as high. Even if fired at the same rate, a satellite based laser would cover a much larger area per pass. Fewer rays, and fewer angles used to shoot past leaves. But, the same principle would apply. could be a very useful tool. Survey land use and plant growth worldwide.

fretslider
March 4, 2021 4:15 am

“…scientists calculated that reservoirs made up 57% of the total global variability of water storage”.

Was that supposed to be a joke?

Last edited 4 months ago by fretslider
Clyde Spencer
Reply to  fretslider
March 4, 2021 8:03 am

It is ‘science’ because they can put a number on it!

DMacKenzie
Reply to  fretslider
March 4, 2021 8:13 am

Are they counting the Great Lakes as a reservoir maybe ?
https://www.visualcapitalist.com/worlds-25-largest-lakes/

Paul S.
Reply to  fretslider
March 4, 2021 9:19 am

97% of scientists believe that

stinkerp
March 4, 2021 4:16 am

Golly, humans store water during wet seasons and use it during dry seasons? What will they think of next? Indoor plumbing? Sliced bread?

George V
March 4, 2021 4:18 am

I will be interesting to see what the technology shows for long term variations after maybe 20 years. I’ve fished the inland lakes in my area for decades (Southeast Michigan) and the variation can be sometimes over 2 feet over several years at times.

But in other news, the headline “Government scientist shoot lasers from space at people to make them more docile and receptive to propaganda! Buy this chrome helmet for 4 easy payments of $49.99!” will appear in 3..2..1…

Peta of Newark
March 4, 2021 4:30 am

You know what I’m gonna say/ask..

What About The Soil/Dirt – and all the water that is/was/could/should be stored there?

NASA: If you really are as clever as you make out, with your Sputnik and lasers, howzabout zapping the stinking little pools & ponds of stagnant water = the ones where mosquitoes live/breed?

Last edited 4 months ago by Peta of Newark
RLu
March 4, 2021 4:34 am

Maybe a strange idea…
… but can they use the exactly known height of fresh water bodies, at a known date and time … to calibrate satellites. That way, you can measure orbital decay.

fretslider
March 4, 2021 4:38 am

 It’s incredibly exciting to see what questions people are able to investigate

Penn And Teller Get Hippies To Sign Water Banning Petition – YouTube

Steve Keohane
March 4, 2021 5:52 am

With an average of 8.6″ of seasonal, natural, fluctuation, there would seem to be a lot of unaccounted for water. We get about 18″ annually in the high, south western plains where it is very dry. We are told the aquafers are being depleted, so the extra water is just evaporating and running into the oceans, not going to ground.

H. D. Hoese
March 4, 2021 6:41 am

“The team used Landsat-derived, two-dimensional maps of bodies of water and their sizes, providing them with a comprehensive database of the world’s lakes, ponds, and reservoirs. Then, ICESat-2 added the third dimension – height of the water level, with an uncertainty of roughly 4 inches (10 cm)”

From the abstract-“We find that seasonal variability in human-managed reservoirs averages 0.86 metres, whereas natural water bodies vary by only 0.22 metres.” Do they really understand that reservoirs are three-dimensional? When satellites first went up the criticism was that it only did 2-D, 3D has finally been established in the GOM.

Obenour, D. R., et al.. 2013. Retrospective analysis of midsummer hypoxic area and volume in the northern Gulf of Mexico, 1985−2011. Environmental Science and Technology. 47:9808−9815. dx.doi.org/10.1021/es400983g ”

wadesworld
March 4, 2021 6:49 am

Cooley and her colleagues found regional patterns as well – reservoirs vary the most in the Middle East, southern Africa, and the western United States, while the natural variation in lakes and ponds is more pronounced in tropical areas.”

Wait…she’s saying some of the most arid regions on the planet utilize the most water? I would never have guessed….

MarkW
Reply to  wadesworld
March 4, 2021 7:44 am

I believe they are saying that dry areas have the greatest amount of seasonal variation in rainfall.

Jim Gorman
March 4, 2021 7:20 am

“When those measurements are averaged over thousands of lakes and reservoirs, the uncertainty drops even more.”

Hate to be a broken record, but when measuring different things and averaging them uncertainty doesn’t “drop”, it is additive by root-sum-square. I am pretty sure these are folks with basic statistical training that ardently believe in dividing by either “N” or “sqrt N”.

Even then, you are finding the mean of independent variables so while the means of various bodies may be added, the variance of the combined means also increases. Stating a mean with also stating the variance is not scientific. One must be able to discern how well the mean describes the entirety of the data.

Jim Gorman
Reply to  Jim Gorman
March 4, 2021 7:30 am

“Stating a mean withOUT also”

Geoff Sherrington
Reply to  Jim Gorman
March 4, 2021 3:40 pm

JG,
Agreed.
Have the statistical requirement of IID been eliminated from science? It is oh so easy to simply assume that your billions of measurements on altitude are IID, but are they? Geoff S
https://www.statisticshowto.com/iid-statistics/

MarkW
March 4, 2021 7:36 am

This “survey” suffers from the same problems that the sea level measurement by satellite does.
If you want to know the height of the water to within one inch, first thing you need to do is know the height of the satellite to a small fraction of an inch. This is impossible.
Secondly you have to know exactly how much the atmosphere is affecting the transmission speed of the laser light.
Thirdly, you need to know how waves are affecting the average height of the water.

Editor
March 4, 2021 8:45 am

It would seem to me that information about pond levels, especially ones that are invariant like reflecting pools in DC or the Christian Science pool in Boston could be an important calibration reference for nearby sea surface levels.

OweninGA
March 4, 2021 8:53 am

How do they account for silting over time. My farm pond is about 3 feet shallower than it was 50 years ago. I am sure mine isn’t the only one that does that either.

Joel O'Bryan
March 4, 2021 10:37 am

They won’t know anything for at least a decade, probably 3 decades.

Steve Z
March 4, 2021 10:57 am

Without dams that slow down spring runoff from melting mountain snow, California’s Central Valley would be a desert, instead of a rich source of fruits and vegetables.

The same is true of the valley south of Salt Lake City, where canals and reservoirs slow down the water flow and provided water for irrigation through the long, dry summers since about 1850, and fresh water for urban populations more recently, since the nearby Wasatch Mountains receive much more snowfall than the valley. The snow in the Wasatch Mountains is basically water that evaporates from the Great Salt Lake and precipitates downwind as fresh-water lake-effect snow. If the water is not captured before it flows into the Great Salt Lake, it is basically lost for consumption, not only by humans but also by any plant or animal life.

Human beings trying to capture water during rainy seasons to be used during dry seasons is nothing new. The Roman Empire built many aqueducts over 2,000 years ago to transport fresh-water runoff from the Alps to cities along the Mediterranean coast with much drier climates. When in a Rome-like climate, do as the Romans did.

Michael in Dublin
March 4, 2021 11:14 am

Three years ago Cape Town was in dire straits because of the low levels of dams with the largest dam around 20%. Three good winters and this dam, the Theewaterskloof, is roughly 80% full with the winter rainfall season due to begin in a month.

Down the coast at Port Elizabeth the situation is more precarious because of having less storage dams. The main dam is at 6.5%. But it is not merely a rainfall problem. The management of the water resources by the municipality has contributed massively because of incompetence.

South Africa swings between droughts and floods. In the past those with foresight built dams that stored huge amounts of water that helped both urban dwellers and farmers during the dry years. However, despite the population growth of 60% since 1990 there has been surprisingly limited building of dams. Instead of wasting money on trying to engineer climate, it would be of immediate benefit to capture some of the huge amount of water that runs off from the flooding.

Michael in Dublin
Reply to  Michael in Dublin
March 4, 2021 11:36 am

I should have mentioned that this Port Elizabeth water supply, the Kouga dam was completed in 1969, 52 years ago. Since then the population has trebled. This dire situation is largely because of mismanagement and incompetence of the Socialist/Marxist leaders and their appointed cronies.

Geoff Sherrington
March 4, 2021 3:47 pm

We find that seasonal variability in human-managed reservoirs averages 0.86 metres, whereas natural water bodies vary by only 0.22 metres.”
The human-managed reservoirs are designed to be operated at variable levels.
Many natural water bodies – not all – have a self-levelling mode. If water flows in faster, it flows out faster into the stream or river that drains it. Maybe this class of lake or pond skews the result that is supposed to show the difference between natural and human-made bodies. And, by the way, many of those human-made bodies digested earlier natural lakes, skewing the comparison again.
This is really sloppy work. Geoff S

observa
March 6, 2021 11:56 am

“Understanding that variability and finding patterns in water management really shows how much we are altering the global hydrological cycle,” said Sarah Cooley, a remote sensing hydrologist at Stanford University in California, who led the research. “The impact of humans on water storage is much higher than we were anticipating.” 

Will our interference in Gaia’s perfect hydrology ever cease?
Dredging the Coast Is Making Flooding Worse, a New Study Says (msn.com)

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