Earlier this week, two wildfires started ripping through Southern New Mexico. Within just 24 hours, they had scorched thousands of acres. 1,400 structures had been damaged. More than 8,000 residents had to evacuate. At least two people were killed. He was trying to get away from the fire as fast as he could, but with a broken leg and a brace, using a walker, trying to carry what you could. It's heartbreaking to know that he didn't make it. Again, this all happened in just 24 hours, and not long after, severe thunderstorms dumped buckets of rain on the charred area, triggering flash flooding. Talk about whiplash. Elsewhere in the US, many cities in the northeast saw days of extreme heat way earlier than usual. A tropical storm off the Gulf of Mexico churned up storm surge on the South Texas Coast. Scientists continue to sound the alarm here. Human-caused climate change is making these extreme events more likely. We're already feeling those impacts on the personal level. But what happens when climate chaos starts pitting world governments against each other? My guest today is CNN senior climate writer, Laura Patterson. She has the story of how a war over water is already playing out along the US-Mexico border.

From CNN, This is one thing. I'm David Ryan. Laura, it is absurdly hot in the US this week, and I realize warm weather in mid-June is not exactly breaking news. Can you Can you just explain why this heatwave is so noteworthy to people like yourself who follow this stuff so closely?

Sure. Well, it's prolonged, it's expansive, and it's early. There's this massive heat dome parked over Eastern US. Temperatures are pushing upwards of 90 degrees. These are temperatures that you might expect more in the hottest days of July, so in peak of summer.

Summer is still days away, but a big chunk of the US is already hot as an oven.

More than half- But they're happening now much earlier, and the heat is likely to intensify. We're seeing parts of the Midwest or the Northeast that could see the longest heatwave they've experienced in decades.

According to the National Weather Service, it has not been this hot for this long in Pittsburgh in 30 years.

Look at that. It's also going to be affecting places that don't have AC, where a lot of people don't have AC. So that means they're much more exposed to this heat, which is a really scary thing. Obviously, this is not just a US phenomenon. It's happening in lots of parts of the Northern hemisphere.

In India, during recent elections, at least 33 poll workers died of heat stress on the same day.

At least 41 Jordanian Ukrainians perished as they made their pilgrimage to Mecca, where yesterday they set a new all-time high at over 125 degrees.

Hundreds of pilgrims have died in Mecca, where temperatures reached well over 120 degrees Fahrenheit. China, India, parts of Southern Europe, like Greece, have also faced these brutal early heatwaves.

At least three tourists lost their lives simply by hiking without enough water or shade.

It's just a really alarming sign, but not a surprising one because the science is really clear that as humans keep warming the world, as we keep pushing up temperatures, keep burning planet heating, fossil fuels, heat waves are only going to get more severe, more prolonged, more frequent. One of the things that I've been at in my reporting is how heat and drought are affecting the relationship between Mexico and the US in an interesting way.

What did you find?

Mexico and the US obviously share a border, and a large part of that border is made up of the Rio Grande. There is a treaty between the two countries under which they agree to share water resources. Under the terms of this 80-year-old treaty, the US shares water from the Colorado River and Mexico shares water from the Rio Grande. But Mexico has fallen a really long way behind in its deliveries. It's supposed to be delivering on these five-year cycles, and we're more than four years into the current one, which ends in October 2025. Mexico has delivered just over a year's worth of water in that time. Obviously, it's a long way behind on- Way behind. Way behind. It's causing some serious issue, and rhetoric is getting quite heated.

They're well behind on these deliveries. Is it as simple as the planet is hotter, there are more droughts, That means less rain and therefore less water for Mexico to give, or are there other factors at play here?

Well, it's always complicated when it comes to water. There's always a tangle of complicated factors. Here, development has a lot to do with it. A lot of towns, farms, industry have popped up either side of the border, and that's increasing demand on water. But then you add the climate crisis on top of that, and it just makes everything that much worse. We know that climate change It is fueling longer, hotter droughts, longer, more severe heatwaves, and that's leading to diminishing water resources. It's causing a lot of pain in Mexico. Farmers are struggling. Mexico City looks like it potentially could run out of water, have a day zero, potentially even this month, according to some. It is a really fraught, difficult issue. But the pain is on the other side of the border as well, obviously.

As it stands right now, we're in the fourth year of the treaty, and they have just delivered a little over one year's worth of water. One year's worth of water is 350,000 acre feet to the US, which is one-third of the flow that comes down the Rio Grande from the Rio Canchos.

Is that what destroyed the business here?

That's what destroyed the business here, because without water, we can't grow sugarcane.

So Mexico's water deliveries go to Texas. And farmers in South Texas are saying, We are really concerned about our future. We don't have enough water. The citrus industry is struggling. The state's sugar industry has been particularly hard hit.

And so a lot of these people that work for us have worked here their entire working career, and it's super difficult to have to tell 500 people that their job won't be here anymore.

Farmer Tudor Ulhunt told my colleague, Rosa Flores, that the state's only sugar mill closed last February, and the industry is basically dying Texas, and he firmly blames the lack of Mexican water deliveries for that.

This has occurred under Republican administrations, and it's recurring right now under a Democratic administration. It's the State Department that interprets the treaties for the United States and is responsible for enforcing those treaties.

There's actually no enforcement mechanism under this treaty, but some Texas politicians are actually calling on the Biden administration to implement punitive measures, to basically withhold aid from Mexico until those deliveries are made. Mexico, some politicians are saying, Well, we cannot give you what we do not have.

It's like, We just literally don't have any water. How are we going to deliver it?

Right, exactly. Things are really difficult for us. The Mexican government has said, We will fulfill our obligations. We will provide water by the end of October 2025, but it's a huge amount of water to give, so there are real concerns about this.

Sugar cane is a canary in the coal mine. We're the first to go, but there are thousands and thousands of acres of citrus and vegetables, cotton, corn, sorghum, Sesame, all kinds of crops that are grown down here that require irrigation. Right now, we're out.

What could be done? It does seem to me like part of the problem, It is that this treaty is like 80 years old and it was not written with climate change in mind. So could they just rewrite the thing to take drought into account? Like, what do you do?

You're absolutely right. So yes, this is a decades old treaty. It was based on data from the first half of the 20th century. So it did foresee drought. That's why Mexico is delivering on these five year cycles. The Rio Grande is unpredictable. We've known that for a long time. But what it didn't foresee are these multi-year mega droughts, and that's a real problem. But in terms of a whole It's a sell renegotiation. It seems really unlikely. It would be opening up a bag of worms, and people build reliance on these treaties. If you think you're going to get a certain amount of water, you set up a town or a farm or an industry, you depend on that. If that then gets taken away, That's real pain.

It's like the long-term planning, this stuff is baked in.

Exactly. There are ways to amend the treaty. There's a process called the Minute Process, and both countries agree to amendments. There are discussions at the moment about an amendment, a minute, which would aim to get Mexico to deliver more regularly, more reliably. Those discussions are carrying on at the moment. Mexico has actually just elected a climate scientist for a president, and she has pledged to prioritize water issues. There's hope that there could be negotiations that help smooth relations, help try to make delivery of this water easier. In the medium term, they're talking about things like drought resilience measures, protecting, preserving, conserving water resources. But in the short term, there's not actually a huge amount that they can do. It's a pray for rain approach. The rain has actually come now to areas of South Texas and Mexico, which could help replenish these water resources. But it might end up being too much of a good thing with the risk of flooding as rain falls on really parched ground. But experts say, Anyway, waiting for rain is not a good long-term strategy. We can't just keep praying for rain to help alleviate these problems. I think it really does shine a light on this much bigger issue of how we share these shrinking water resources when the world is just getting hotter and drier.

Yeah, I was going to say, even beyond North America, are world governments thinking about how to share water as it becomes more and more of a scarce resource?

I think it has to be top of mind for governments thinking about how we deal with this, because we do know that climate change is going to be affecting extreme weather, like heat and drought.

As if the deadly wildfires in New Mexico weren't destructive enough, now, thunderstorms are causing dangerous mudslides and flooding, making a hazardous situation even worse for first responders and, of course, residents.

We're just going to be seeing this huge unpredictable where we might see massive flooding, rivers bursting their banks. One month, the next month, we're seeing these really severe droughts. So thinking about sharing water resources, thinking about how to to protect them, how to build in drought resiliency is just going to be so important going forward.

Yeah. And like we see with so much of the climate change discussion, it's how to address some of these problems while not exacerbating already existing inequalities. Laura, really great reporting. Thank you.

Thank you so much.

One Thing is a production of CNN Audio. This episode was produced by Paula Ortiz and me, David Reind. Our senior producer is Fez Jamil. Our supervising producer is Greg Peppers. Matt Dempsey is our production manager. Dan Dizula is our technical director, and Steve Ligtai is the executive producer of CNN Audio. We get support from Haley Thomas, Alex Manessari, Robert Mather's, John Dianora, Lanie Steinhart, Jamie Sandrace, Nicole Pessereau, and Lisa Namerau. Special thanks to Katie Hinman. We'll be back on Wednesday, and make sure you're following the show. It's a big week for us. Cnn is hosting the first presidential debate down in Atlanta. I will be there to cover it all, so stay tuned for all that. I'll talk to you later.