Why the planet is drying out much faster than before, according to a new study

Ali Rogin:

The planet is drying at an unprecedented pace, presenting a critical threat to humanity. That's according to a new study published in the Journal Scientific Advances. Researchers found that continental drying is having profound global impacts that threaten water availability across the globe.

For part of our Tipping Point coverage, I spoke recently with Abrahm Lustgarten, climate Investigations Editor at ProPublica, and began by asking him why so much of the Earth is drying out.

Abrahm Lustgarten, ProPublica:

It's a mixture of climate change and a massive overuse of water resources by people that appears to be drying out the continents, according to a new study out of Arizona State University. And it basically found that rising temperatures are leading to less precipitation in certain places and faster evaporation from both the soil and from rivers and surface waters. And at the same time, that over pumping of groundwater aquifers is quickly depleting the resources that are held in those underground reservoirs.

Ali Rogin:

Who's driving this problem?

Abrahm Lustgarten:

It's difficult to parse out the difference between climate change, as in effect, and the human over pumping of groundwater. But those are the two factors. And of course, you know, it's the emissions from the burning of fossil fuels that is driving the rising temperatures on the planet. And so that is really contributing to a water loss or a water reapportioning across the globe.

And the groundwater pumping is driven by individual use by farmers, by corporations, by cities around the world. It is becoming the fallback kind of bank account, if you will, of water resources that people and groups are turning to as their surface waters are diminished or as droughts deplete those surface waters for a shorter period of time. People are looking to those underground reservoirs and pumping more, pumping faster, exploring deeper.

Ali Rogin:

And the study uses NASA satellite images over the course of 20 years to track the evolution of land that's drying out. Can you walk us through mechanically how that works how those satellite images were able to capture this change, it essentially.

Abrahm Lustgarten:

Measures changing mass in the spinning Earth, changes in the Earth's rotational orbit, so it can measure how much volume is in the ice caps on the poles and how much water is underground, and then changes in.

And over the last 20 years, it's allowed researchers to be able to tell the difference between one type of changing mass and another. So now, really, for the first time, these researchers are using that grace satellite data to get a sense of the Earth's total water supply and then to distinguish between how much of the loss of that water supply is from melting glaciers, from climate change, for example, and how much is from something like groundwater depletion.

Ali Rogin:

What are we talking about here in terms of total water loss? And also how has this accelerated over the past 20 years?

Abrahm Lustgarten:

So the researchers caution that they don't know where the bottom is, so to speak. So we don't have a precise measure of how much fresh water there is to work with. But what we do know is that the accounts that we're working with are quickly being withdrawn. So we can see that the rate of drying that they measured has quickly accelerated just over the last 10 years or so. Since 2014, they've been measuring for 22 years. They've seen that rapid depletion from the very beginning, but it has intensified and accelerated just in the last 10 or 12 years.

And so that's particularly alarming. It's something that led them to write in their paper that this issue is a critical and emerging threat to humanity.

Ali Rogin:

What do we know about where this is affecting the globe? Is it happening more in certain parts of the world, or is it pretty evenly distributed?

Abrahm Lustgarten:

The study found that drying places are getting drier faster than wetting places are getting wetter. And it found that those drying regions are much, much larger than the places that are getting increasingly wet. And those drying regions are spread across every continent. There are substantial drying regions, which the researchers now describe as mega regions, that constitute much of the southern United States and into Mexico and Central America.

There is a mega drying region that they identified that covers pretty much the whole of Europe and into the Middle East and includes parts of North Africa, and again, a large swath of South Asia is also part of these mega drying regions.

And what those mega regions constitute is the merging of places that already were known to be losing water or suffering from drought, but they used to be finite or distinct places. We used to think, for example, of the southwestern United States as being particularly dry, which it is, and suffering from climate change, which it is.

But until recently, we didn't understand that drying region was spreading across the whole southern part of the country and is extending down into Mexico and into Central America, and that it's becoming one large drought plagued or drying out region.

Ali Rogin:

How much are we able to connect this phenomenon we're seeing around the world with the impact on the inhabitants who live in these parts of the world? Are we seeing this play out in real world implications right now?

Abrahm Lustgarten:

Yeah, absolutely. I mean, the water loss that this research identified is mainly occurring in mid latitude regions, which is where most of the population of the planet resides. And the researchers identified water net loss in 101 countries. And those 101 countries happen to be home to about 75 percent of the planet's population. So about 6 billion people live in the regions that are on balance, losing access to fresh water.

Ali Rogin:

Abrahm Lustgarten, Climate Investigations Editor at ProPublica. Thank you so much.

Abrahm Lustgarten:

Thank you.