In the 19th century, early white settlers considered the Rio Grande Valley, where the once-mighty Rio Grande defines the border between the United States and Mexico, to be a forest of thorns and cacti where tarantulas crawled into your boots and ocelots slinked by just beyond the campfire.
Nomadic tribes of Native Americans had thrived in the Valley for centuries, and both Spanish and Mexican soldiers had long been marching through the region. But among the waves of settlers from the East Coast and the Midwest who came looking for farmland, few people thought the region would be good for much beyond cattle.
Then around the turn of the 20th century, ditches were dug in the banks of the Rio Grande to let water irrigate the land. Because it was hot, farmers planted sugarcane, which grew well in the tropics. It flourished. And landowners in the Valley realized that with a little water, this was an agricultural paradise. There were no big winter freezes and a long growing season, with plenty of sunshine and rich river-bottom soil.
With water, they discovered, heat could be tamed.
Soon there were canals everywhere and grapefruit trees and tomatoes and corn and cotton and lettuce. Whatever you planted, it grew. A nickname emerged for the Eden-like region: the Magic Valley.
And for the last hundred years or so, it has been magical. The Rio Grande Valley — which, in fact, isn’t much of a valley at all, just a big flat expanse of river-bottom land created over centuries by the ever-changing Rio Grande — is one of the most agriculturally productive regions in America, growing everything from watermelons for Fourth of July picnics to sorghum for animal feed to papaya for salads and smoothies.
But when I visited the Valley in 2022, the Southwest was suffering from the worst drought in 1,200 years. According to the U.S. Drought Monitor, 99.8% of the region was in “extreme drought.” Decreasing snowpack in the Rockies had diminished the Rio Grande’s headwaters. Golf courses and condos along its banks, as well as farmers who grow water-intensive crops like pecans, leached the river’s flow. The water that is left is increasingly salty and tainted by nitrogen runoff and other pollutants.
As the heat rose, good water was needed more than ever. But there simply wasn’t enough to go around anymore.
“When you cut the water off, everything changes. Not only nature, but you change people’s way of living, the economy, the biodiversity,” says Estela Padilla, 77, a retired state worker who has lived along the river her entire life. “It is so colossal. It’s like a crime scene.”
The challenge the Valley faced was at once local and global. All over the world, extreme heat is hurting crop harvests and driving hunger. Since 2019, thanks in large part to global warming and the war in Ukraine, the number of people facing acute food insecurity has soared — from 135 million to 345 million. To meet the expected demand for food by midcentury alone, global agricultural output will have to rise by more than 50%. But that output will have to grow as global temperatures rise, threatening crop productivity.
In the Rio Grande Valley, the river that drives agriculture in the region is shifting, becoming more polluted and drying up. Droughts like the one in 2022 have forced farmers to limit watering. Extreme storms, including once-rare major freezes, are damaging crops.
Farmers in the region don’t talk about the impact much — “it usually only happens after several shots of tequila,” said Alexis Racelis, an associate professor of agroecology at the University of Texas Rio Grande Valley. Instead, they practice what amounts to a just-in-time adaptation strategy, shifting to different crops and planting times as conditions change, he said.
But questions linger over what will happen if the heat keeps rising and water keeps becoming more scarce.
Racelis lives in a 1960s suburban-style house with a big mesquite tree and a shaggy vegetable garden in the front yard. When I arrived at 7 a.m. one morning in early 2022, he was up and loading gear into his black Nissan Pathfinder. He’s 46. He was wearing a khaki shirt and well-worn work boots, and if you didn’t know who he was you would guess he was a farmer.
Racelis, the son of Filipino immigrants, grew up in San Diego and, after getting his Ph.D. at the University of California, Santa Cruz, he went to work for the U.S. Department of Agriculture, focusing on invasive species. At UT-RGV, he spends most of his time working with farmers to find ways to grow food with less water and less dependence on Big Ag for seeds and fertilizer.
“We have a long growing season here, which has always been a big advantage,” he told me as we drove out of town in his Pathfinder. “But in the summer, it’s so hot that it’s basically our fallow season.”
Nothing can bear fruit when it gets above 95 degrees, which it does from May to September. And the number of hot days is increasing. Racelis said farmers face a challenge of getting the crops in and out of the ground before it gets too hot in the spring.
“If this heat keeps up,” he said, “broccoli and cauliflower is going to start bolting, which is a big problem.”
Racelis drove 45 minutes across fields of onions and watermelons, as well as giant squares of land waiting to be planted with sorghum and corn, before we arrived at a 700-acre aloe farm. It was a beautiful place, with a row of palm trees on the main road and a big farmhouse nestled in some trees on a small hill. The temperature was a balmy 92 degrees. Not bad — except that it was February.
Out in the field, we met Andy Cruz, a 40-something man in rough, muddy boots who was in charge of growing things on these 700 acres. He had been a farmer in the Valley all his life, he told me, and had grown all kinds of food. Now, those 700 acres were growing exclusively aloe. Aloe is not primarily a food crop (although people do use it to cook, and for flavor in yogurts and desserts). It’s grown mostly for the aloe vera gel that is found in the leaves of the plants, which has been used for thousands of years for skin care and other health reasons.
By all accounts, aloe should be the perfect crop for the Valley. To begin with, it’s a succulent — a plant with thick, fleshy tissue that’s well adapted to water storage. It evolved in the heat of Africa and, like many succulents that emerged in hot places, it has developed a unique capability to in effect hold its breath during the heat of the day and breathe only at night when it’s cooler. During the day, the aloe’s stomata — the small mouthlike structures on the underside of plant leaves and stems — close up tight, minimizing the water loss that would otherwise occur while the plant is inhaling CO2. Then at night, when the temperatures are cooler, the stomata open and the plant breathes.
Aloe has another, even more remarkable heat adaptation: if it gets too hot and dry for too long, the plant can put itself into what amounts to a temporary hibernation, slowing down its metabolism to the point that its water and CO2 needs are minimal. Then when it rains, or sufficiently cools down, the plant wakes up and comes back to life.
Despite these wonders, the 700 acres of aloe have been a world of trouble for Cruz. For one thing, a plant that’s well adapted to heat is not necessarily well adapted to the lack of heat. A cold snap in the Valley in the winter of 2020 killed half his plants. “It was bad,” Cruz told me. “We were out here for two days and nights with burners trying to keep things warm. This climate change thing is making the weather like a Ping-Pong ball — you never know where it is going to bounce.”
But even the cold weather giving Cruz problems might be the result of a warming world. The Arctic is warming four times as fast as the rest of the planet, and as a result, it is pushing the jet stream farther south, allowing the cold arctic air to move down to Texas.
“Up until five years ago, things were fairly predictable,” Cruz told me. “But now, you never know what’s coming. It’s different. Something’s changed.”
In struggling to keep his aloe alive, Cruz had already moved on from growing a crop that might have gone further to address global hunger: corn. The Texas A&M AgriLife Extension lists corn as one of the main field crops grown in the Rio Grande Valley. Farmers were growing it on more than 100,000 acres in the region in 2019. But of all the commercial food crops, corn may be the most vulnerable to heat.
It does have some advantages, however. Most plants use what’s known as C3 photosynthesis to convert sunlight into food (it’s so named because the carbon compounds produced contain three carbon atoms). But C3 photosynthesis is problematic because about 20% of the time, these plants make a mistake and instead of a carbon molecule they grab an oxygen molecule, which is useless to them.
Corn is a C4 plant (others include sorghum and sugarcane, two of the other four main field crops in the Rio Grande Valley), which uses a different process that avoids the mistake of confusing oxygen with carbon. That makes the plant’s metabolism more efficient. Also, similar to aloe and other succulents, it closes up its stomata on hot days, allowing it to conserve water and better tolerate heat (corn moderates its breathing depending on temperature, while aloe breathes only at night, regardless of temperature).
Like aloe and other succulents, corn evolved in a warm place. Its wild ancestor, a grass called teosinte, thrived for 10,000 years in the Balsas River Valley in south-central Mexico, where the temperature is a steady 80 degrees. That means that deep in its ancestral gene pool, it has more tools to handle heat than many plants.
But 80 degrees is very different from, say, 102 degrees. As the world heats up, corn is nearing the limits of its adaptive (or “permissive”) temperature range. To put it another way, it’s already growing in hot places and now those places are getting hotter. Add a modest heat wave to those already hot places and corn has trouble coping. Add an extreme heat wave and it may not recover at all.
Corn is in particular trouble if that heat wave hits during the reproductive cycle. “Heat disrupts the development of the pollen tube, which is deployed from the pollen to deliver the sperm into the female plant’s ovule,” said Donald R. Ort, a plant biologist at the University of Illinois, Urbana-Champaign. “So the plant never fertilizes, there is no ear.”
Corn is also vulnerable because, at least here in the United States, big seed companies like Monsanto and BSF have had their way with the corn genome for years. Growing it requires huge amounts of nitrogen fertilizers, which end up polluting rivers and lakes, causing huge algae blooms. In the right conditions, commercially bred corn is a superstar. But if heat spikes and rains don’t come at the right time, it’s vulnerable. In the highly engineered varieties of corn that most farmers grow, much of its rich genetic diversity has been bred out and what is left is an army of high-yielding inbred hermaphrodites, exquisitely suited for a narrow range of conditions that exist in the Corn Belt. Or that existed there before climate change started making a mess of the weather.
In July 2022, corn growers across Texas began harvesting a couple weeks early because high temperatures caused plants to mature ahead of schedule. John Paul Dineen in Ellis County, near Dallas, said his 700 acres of corn were “pathetic and scraggly.” He’d walk out in the field and peel back an ear and it was dry and hard and only half covered with kernels. There wasn’t much to harvest. The stalks were only 5 feet tall at most, compared with 6 to 7 feet normally. “Yields are 50% of an average year,” he said. “We might get 50 bushels per acre,” which was far below the usual 100 to 110 bushels.
By midsummer, according to the U.S. Department of Agriculture, 42% of Texas corn acreage was in poor or very poor condition. Only 3% was in excellent condition. David Gibson, executive director of Texas Corn Producers, a trade group, said the heat and the drought had been devastating for many farmers even though the market price for corn was high.
“When you’ve got no corn to sell, a good price doesn’t keep you in business,” Gibson said.
So why not just plant corn in cooler places? It’s not so simple.
“If you plant corn in the Central Valley in California and you give it unlimited water, it does amazingly well,” Jeffrey Ross-Ibarra, a corn geneticist at the University of California, Davis, told me. “It’s just not economically feasible. The profit margins are such that you’d rather be growing grapes or almonds or something in California if you’re going to spend a lot of money on water. So I don’t think it’s as simple as saying temperatures are going to push everything north and we’ll be fine, because it is a combination of soils and water and government regulations and agronomic practices and even contract preferences.”
The vulnerability of corn matters because it’s the industrial food stock of American life. Processed foods, from breakfast cereals to ice cream, are saturated in corn syrup. Corn is a prime feedstock for animals, which have themselves been engineered to ingest and digest huge amounts of corn and transform it into animal protein. In this sense, a McDonald’s hamburger is better thought of as a McDonald’s corn burger. Corn fuels your trip to McDonald’s, too. More than half the corn grown in Iowa actually ends up as ethanol, which is mixed with gasoline and is an essential ingredient in fuel.
If corn productivity declines, there will be more pressure to clear land to grow more, which is bad news for places like the Amazon rainforest. It will also raise prices for many food staples, especially meat. How exactly that will play out will be different in different places at different times. But as the Russian invasion of Ukraine demonstrated, higher food prices are inextricably linked with political instability, chaos, and war.
Racelis and I drove out to a 12,000-acre ranch on the western edge of Hidalgo County. He wanted to check in on an experiment he was running that measured the effectiveness of cover crops at keeping moisture in the ground. The temperature had dropped 40 degrees overnight and there was a slight drizzle, which, given the epic drought the region was facing, was a good sign. Racelis talked about how farmers were waiting for one heavy rain before putting crops like cotton and sorghum in the ground.
“Growers have been informed that there is enough water for them to have one good watering this year,” Racelis explained. “Usually they get two or three. So if they can, they want to wait to plant until we get a good rain, so they can save their irrigation water for later in the spring when they really need it.”
“That said, growers here are very resourceful,” Racelis explained. He talked about how farmers practice what amounts to a just‑in‑time adaptation strategy, shifting to different crops and planting times as conditions change. “Things like okra will always grow by the river, as long as the river is flowing,” he added. “But how much okra does the world need?”
After about an hour, we turned down a narrow farm road. In the distance, I saw three or four people out in the field, a few trucks pulled over on the side. We parked beside them, then walked into the field. Racelis introduced me to a few of his students, then to some farmers he was working with. One of them was Avan Guerra, a weathered-looking man who wore his jeans tucked into his boots. He is a former parole officer who got into farming and now has 300 acres. Guerra owns his own tractor and other equipment. He grew up here, and remembers the heat when he was a kid, but it didn’t seem that bad back then.
“Nobody used to need air-conditioning to live around here,” he said. The erratic weather is not just making it tougher for his crops. It’s also making it tougher for him to decide every year what to put in the ground. “I hope to get another decade out of this, and then I’m heading to Vegas,” Guerra told me, smiling.
Genetically modified crops, alternatives to corn like Kernza (harvested from a wheatgrass perennial that continues to grow for a decade or two after it is planted), growing crops in climate-controlled greenhouses — these ideas have all been floated, and are worth investigating, but none of them promises to offer immediate relief.
“People will shift crops around, try new varieties,” Racelis told me as we drove around the Valley one day. “But in the end, there is no getting around the laws of physics and biology. When it gets too hot, things die. That’s just how it works.”
Disclosure: Texas A&M AgriLife has been a financial supporter of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune’s journalism. Find a complete list of them here.
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