As It Happens

NASA study reveals humans are dramatically shifting global freshwater sources

Scientists at NASA have used a map of Earth's gravitational field to study the movement of water around the planet — and their findings have human fingerprints all over them.

For 15 years, NASA used satellites to track global freshwater movements

Using satellite imaging, NASA has mapped the way humans have altered the movement of water across the planet. (NOAA/NASA GOES Project/Getty Images)

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Human activity is having a huge impact on how wet the earth is — so much so that it's affecting the planet's gravitational field, according to researchers at NASA.

A myriad of factors is affecting where water can be found around the world, from massive ice loss in the Arctic, to bloating in flood-prone parts of Canada, to potentially damaging dam construction in China.

Matthew Rodell is the lead author of the study, which was published Wednesday in the journal Nature. He's also chief of hydrological sciences at NASA's Goddard Space Flight Centre. As It Happens host Carol Off spoke to Rodell about the implications of the dramatic shifts.

Here is part of their conversation.

Mr. Rodell, how quickly is the water around us changing?

Well, what we did was we studied 34 regions around the world using NASA's GRACE [Gravity Recovery and Climate Experiment] satellites. We found that in those regions some of the most prominent changes were the ice sheets melting. But then some of the other big changes were groundwater depletion around the world caused by water being pumped to irrigate agriculture.

These are huge changes in water storage. So Lake Mead is the largest man-made reservoir is the United States. It holds about 32 gigatonnes of water. Each gigatonne is about 200,000 Olympic-sized swimming pools full of water. The changes that we were measuring were on the order of the size of Lake Mead, during this period, or larger. Ten of these 34 regions experienced changes that would have been about 10 times the size of Lake Mead.

How much of what's happening to this shift in water, this dramatic change, is man-made?

We studied 34 regions around the world where we saw the most prominent changes or trends in terrestrial water storage. Of those, we said that about eight of them were associated with climate change, about 14 were associated with direct human impacts like groundwater pumping and only about 12 of them were caused by natural variability alone.

What are the implications for people living on this planet?

Water is one of our most important resources, if not the most important resource. It's critical that we be able to track its movements around the world and, in particular, in regions that are water stressed. Places like the Southern High Plains in the U.S., or the Central Valley in California, or also Northern India.

These regions are regions that rely heavily on groundwater for growing crops and they are some of the most productive regions in the world for ensuring that there is enough food for the world. In those regions we see groundwater being depleted.

It's unsustainable what they are doing right now. They're pumping too much water out of the ground, faster than it is being recharged. And of course, that's scary when you think about a growing population around the world and the importance of being able to feed them in the future.

What does it say about those regions, like we've just seen in Canada, [that had] a huge problem with flooding in British Columbia? There's a massive amount of water. What happens to those places that are getting too much water?

In a lot of cases when there is flooding, it's just part of the natural variability. One thing that's useful about the data is we can use it to sort of forecast when there may be flooding.

But what climate models predict for the future is that some of the wetter northern latitudes will become wetter in the future, whereas some of the mid-latitude and semi-arid regions will become drier. So, for Canada, that could potentially mean more flooding in the future.

As a hydrologist, you've been watching this for some time. Now you've got this data from the satellites. How surprised were you to learn what you did?

Many people were very skeptical when GRACE first launched that it would be useful for hydrology. But the skeptics have been proven wrong. It's been fantastic. Remember that many countries around the world are not as good about sharing data as the U.S. and Canada are. So we have this data from GRACE that we could not measure in any other way.

Written by Chloe Shantz-Hilkes and John McGill. Interview produced by Chloe Shantz-Hilkes. Q&A has been edited for length and clarity.