- Climate change is making rainfall and droughts more extreme and unpredictable, which means we need groundwater more than ever as a buffer to support us.

When rivers dry up and rain doesn't fall, - Because it's not dependent on the last season's rainfall, it's effectively much more climate resilient.

- But the thing about groundwater is that it's not a renewable resource in the same way that surface water is.

It behaves more like oil.

Once we pump it out, it's often gone for good.

And now scientists warn that we're rapidly approaching a tipping point, something called peak water.

The moment groundwater supply begins an irreversible decline, meaning that each year we'll have less of it available than the year before.

And groundwater is foundational to modern human life.

It supplies nearly a third of the world's fresh water and over 40% of global irrigation.

But now all of these forces are on a collision course: worsening droughts, rising food demand, and shrinking aquifers.

And a new study has modeled exactly when and where global peak water is expected to hit.

And it's not good news for some of the world's most important food producing regions.

In one country, it's gotten so severe, they're moving their entire capital city.

At first pumping groundwater seemed kind of like a miracle, clean, accessible water on demand with no visible consequences.

In the United States, that water has fueled the growth of some of the country's most productive farming regions, including California's Central Valley, Arizona, and the High Plains: regions with hot, sunny climates, perfect for growing crops, but with nowhere near enough rainfall to support large scale farming on their own.

And similar stories have played out across the world, like in Northern India and Pakistan, Mexico, Iran, and across the Middle East: dry regions with fertile land and fast growing populations.

Groundwater is one of our most precious resources, but it's also one of the least visible - Surface water is the water we can see flowing in the rivers and comes from the rain.

Then part of this water infiltrates into the ground and is stored underneath in the porous rock and soil.

And this forms then what is called an aquifer.

- This filling or recharge process is so slow that much of the water stored in aquifers is truly ancient, sometimes tens of thousands of years old, which is why it's often called fossil water that makes it essentially non-renewable on human timescales.

But we haven't treated it that way.

Instead of seeing groundwater as a finite resource, we've pumped it as if it were endless.

So where has that left us?

Well, in California, Central Valley water tables have dropped by hundreds of feet.

In some places, thousands of wells have run dry with entire communities losing access to water.

And in some places, the land itself is sinking by up to two inches per month due to subsidence.

In Arizona, enormous fissures have opened up across the landscape in some cases over a mile long.

Across the high plains, some farmers have had to drill so deep to access water that some wells now cost hundreds of thousands of dollars.

So you might think that as groundwater stress increases, we'd slow our extraction and begin managing it more sustainably.

Right?

Right?

- We're looking at data for 40 countries.

These areas accounted for 75% of groundwater withdrawals globally.

- This was the most comprehensive study ever conducted of its kind.

In total, they looked at data from 178,000 wells.

- It didn't surprise us too much that groundwater levels are declining.

What was really striking for us is that the rate of decline was accelerating in many places.

- In other words, not only are aquifers shrinking, they're shrinking faster than ever before.

So why aren't we managing this water more carefully?

Well, part of the answer at least lies in climate change.

- The groundwater itself is not too much affected by climate change, but the people adapt to climate change and use the groundwater, which they usually would have taken when rain was falling regularly.

- So we find ourselves in a catch 22.

As droughts grow longer and more intense, we rely more and more on groundwater to fill the gap, which only speeds up depletion.

But at the same time, we'll need that groundwater more than ever in the future, precisely because droughts are getting worse, which raises the big question, how far are we from the tipping point?

When groundwater availability peaks and begins its indefinite decline.

This is exactly what a new study set out to understand on a global scale.

A team of researchers ran 900 simulations using one of the world's most advanced human earth system models.

These scenarios explored a wide range of possible futures, different climate trajectories, population growth, energy demands, and water policy.

Well, in nearly all of the 900 scenarios, global groundwater extraction follows a clear peak and decline pattern with the global peak projected around 2050, just a couple decades away, and many of the places most likely to peak are among the most important food producing regions on earth and will expose about half of the world's population to water stress.

These include critical farming regions in the western United States, Mexico, India, Pakistan, and China, as well as several other countries in the Middle East and Mediterranean.

Now, to be clear, groundwater doesn't peak because it disappears entirely.

There's still a vast volume of water beneath our feet, but as aquifers are pumped, water tables fall and that water becomes harder and more expensive to reach, wells must go deeper.

Energy use rises and costs skyrocket.

Eventually, many users hit a breaking point.

Some adapt by switching crops or importing food.

Others stop pumping altogether.

And that's what scientists mean by peak water.

The moment when extraction becomes too difficult, too costly, or too damaging to continue at the same pace.

And in this way, groundwater mirrors the behavior of other depletable resources like oil and minerals.

So if one of the most essential resources for growing food and sustaining life is already entering a phase of irreversible decline, what happens next?

Well, for starters, food is likely to get more expensive.

As water becomes harder to access, these major farming regions may struggle to keep up production, and this doesn't just affect local food security.

It can ripple out to global markets impacting international trade.

And it's not just agriculture that's at risk.

Wetlands and rivers that depend on groundwater can dry out, damaging ecosystems and wiping out habitat.

And as water levels drop, contamination can spread with pollutants like arsenic and salt, concentrating or seeping in from surrounding layers.

And then there's one final impact that's so severe.

It's already caused one of the world's largest capital cities to plan its relocation: subsidence.

And we're just beginning to see its effects in cities all over the world.

- As aquifers are depleted, the structural framework that supports the land begins to compact slowly.

- Compaction happens because as the water is removed, the tiny spaces between soil and rock particles collapse inward, squeezing the ground tighter and tighter.

- Ground subsidence is often one of the most clear physical indicators that a region has surpassed that tipping point, and this compaction can lead to permanent loss of storage capacity.

- Which means that even if groundwater level rises in the future, the aquifer will no longer be able to contain or store the same volume of water that it once did.

In Leonard's study, he focused on the urban impacts of subsidence.

Specifically, he analyzed 28 major US cities all with populations over 600,000.

- And what we found that in all of the cities, they have measurable subsidence from one millimeter per year on average to greater than five millimeter per year.

- Of the 28, the fastest sinking cities were Houston, Dallas, Fort Worth, New York, and Chicago.

- But more significantly in every single city, we found that there are areas that have rates greater than 5 millimeter per year.

- In the cities Leonard analyzed, he found over 29,000 separate buildings that exist in high to very high risk zones.

And these findings matter because when the ground sinks unevenly, it can damage roads, pipelines, railways, and even building foundations.

But subsidence is perhaps the biggest problem for coastal cities because it happens on top of sea level rise.

- You have two major hazards that you have to respond to, and you have increased the frequency of tidal flooding, storm surge, or even total inundation for particular cities - In the United States.

Leonard's study highlights several cities where this is already becoming a concern, including New York, Houston and New Orleans.

But globally, the most dramatic example is Jakarta - Indonesia's capital.

Some parts of the city are sinking by up to 10 to 25 centimeters a year due to heavy groundwater use, soft soils, and rapid urban development.

Today, over 40% of Jakarta sits below sea level, making it dangerously flood prone.

The problem has gotten so severe that the Indonesian government is now building an entirely new capital city.

But as bad as all of this sounds, there's also reason for hope, which strangely might be hidden within part of the problem.

Earlier we discussed how climate change is making the hydrologic cycle more extreme, leading to more intense droughts and also more intense rainfall.

Well, new research is revealing that those very extremes might help us recover if we're paying attention.

- What we were finding was a bias in the replenishment of groundwater to heavy, often extreme rainfall.

- While steady seasonal rain may no longer be as reliable, sporadic, but more intense downpours could still offer excellent opportunities to recharge depleted aquifers, but only if we're ready to capture that water.

That means identifying where the ground is most permeable, protecting open spaces and building infrastructure designed to absorb water, not just divert it.

One way or another, we're going to have to learn how to manage our groundwater more sustainably because droughts are going to get worse in the coming decades, and this resource will only become more essential.