Climate & Environment

Beyond Arrakis: Dune researchers confront real-life perils of shifting sand formations

Daniel William Strain — Mon, 18 Aug 2025 18:50:15 +0000

Beyond Arrakis: Dune researchers confront real-life perils of shifting sand formations Daniel William… Mon, 08/18/2025 - 12:50

Daniel Strain

Elk graze in Great Sand Dunes National Park and Preserve. (Credit: National Park Service)

Last summer, Stephanie McNamara got her first glimpse of Great Sand Dunes National Park and Preserve in southern Colorado. The park is a monument to sand, where dunes stretch across 30 square miles and tower nearly 750 feet high, making them the tallest such formations in North America.

McNamara, a graduate student in geophysics at ɫ��ֱ��, had recently joined a project studying features like these. But it was one thing to read about dunes and another to experience them in person.

“We have what we call saltating grains, which are small sand grains that skip across the surface of the dune. You could feel those on your legs, then, all of a sudden, they’re in your mouth,” McNamara said. “Unless you’re in a dune field, it’s hard to think about everything that’s blowing around.”

The graduate student is part of a research effort led by Nathalie Vriend, associate professor at the Paul M. Rady Department of Mechanical Engineering at ɫ��ֱ��. Among other questions, the lab explores how dunes evolve over time—shifting and surging across the landscape through processes like those that were scraping McNamara’s legs.

The sci-fi classic book Dune, and its recent film adaptations, takes place mostly on the fictional world of Arrakis—a desert planet where sand stretches endlessly in every direction. But dunes abound even on a water world like Earth. Sand dunes occupy an estimated 5% of our planet’s land area. They sit on six continents and come in all shapes and sizes. The most common dunes, barchans, are shaped like crescent moons, while others look like stars or castle walls. Some dunes even sing.

Just like the dunes in the national park, these formations are relentlessly, sometimes stubbornly, alive.

Understanding exactly how dunes move has become an urgent pursuit, Vriend said. The world is growing hotter and dryer, and deserts across the globe are spreading, swallowing homes, farmland and even entire villages.

Vriend’s research group uses a variety of tools, including ground-penetrating radar and computer simulations, to reveal the physics and mathematics that govern dunes. The team ultimately wants to answer a pressing question: Can humans efficiently shift or even halt the flow of the planet’s largest dunes?

“Here in the U.S., we encountered this problem 100 years ago when we had the Dust Bowl, when dust and sand was ravaging through farms and completely destroying harvests,” Vriend said. “We’re still facing this issue today, and, as a result, we need to understand how sediment moves, how it transports.”

Stephanie McNamara at Great Sand Dunes National Park and Preserve. (Credit: Stephanie McNamara)

Desert songs

Vriend had her own moment of discovery early during her time as a doctoral student at the California Institute of Technology in Pasadena. As part of a research trip, the mechanical engineer hiked to the top of one of the Mojave Desert’s famous singing dunes. These dunes create an eerie humming noise that can echo for miles in every direction.

“I remember going down this dune, and this sound started to boom out on the desert floor, and my whole body started to vibrate,” said Vriend, who came to ɫ��ֱ�� in 2022. “Being a tiny part in a big, big landscape like a dune landscape is very humbling.”

Years later, Vriend and her advisor at Caltech, Melany Hunt, helped uncover what makes singing dunes sing—it has to do with how small avalanches of sand vibrate as they slide down the face of a dune.

Vriend and her former graduate student, Karol Bacik, summarized the state of science on the dynamics of dunes in a paper published online ahead of print in the Annual Review of Fluid Mechanics.

She noted that the physics that underlie large dunes is surprisingly complex.

“If [sand] rests on your hand, it forms a little heap, and it’s solid. Then you pour it out, and it acts like a fluid and flows,” Vriend said. “If you throw it up in the air, and the wind is blowing, it flies away like a gas.”

Which all makes tracking the flow of dunes a tricky undertaking. Depending on their size and the prevailing winds, dunes can move anywhere from a few feet to dozens of feet every year.

In a previous experiment, Vriend and her colleagues set out to discover what might happen when the winds blowing on a dune suddenly reverse direction. She led the experiment as a Royal Society University Research Fellow at the University of Cambridge in the United Kingdom.

To simulate the complicated dynamics of a dune field, the team turned to a massive apparatus called a circular flume. The machine is, essentially, a ring of water that measures more than 6 feet across and spins like a turntable. The spinning flume creates underwater currents that wash over piles of sand, not unlike winds blowing in the desert.

The researchers discovered that nearly two-thirds of the dune never moves at all during such a reversal. Instead, only the top layer of sand seems to shift, flowing from one direction to the other—a bit like a baker icing, then re-icing a cake.

Stephanie McNamara works on a dune in Chile where researchers have planted different kinds of obstacles. (Credit: Stephanie McNamara)

Researchers in Chile will explore whether obstacles can shift the path of dunes. (Credit: Stephanie McNamara)

Nathalie Vriend taking samples from a dune. (Credit: Nathalie Vriend)

Grains of sand

Winds blowing over a dune can move grains of sand in three main ways. What path these grains take depends on their size, although the exact size in each category can change from site to site, said Stephanie McNamara, graduate student in geophysics at ɫ��ֱ��.

Credit: Nathalie Vriend

Creep
The largest grains roll and bounce over the face of a dune—a process known as creep.

Saltation
Medium-sized grains undergo a phenomenon called saltation. They jump into the air then land back down, knocking into more grains in the process, somewhat like a game of billiards.

Suspension
Then there are the smallest grains. Winds suspend these particles high in the air like a gas. “They can even leave the dune field,” McNamara said.

Spreading sand

For millions of people around the world, these dynamics aren’t just the stuff of scientific papers or sci-fi blockbusters. Rather, they can become a matter of survival, McNamara said.

In the United States, for example, sand dunes around Lake Michigan engulf houses, roads and other infrastructure. In Mauritania, sand from the Sahara Desert has consumed entire communities and is threatening the nation’s capital of Nouakchott, home to roughly 1.5 million people.

Those trends will likely only get worse in the decades to come, the researchers added.

That’s because, in many regions of the world, deserts are growing and spreading at an alarming rate—the result of a confluence of factors, from warming temperatures due to climate change to human land-use practices like deforestation. According to one study, this rapid “desertification” may have already affected the lives of more than 200 million people.

But can humans efficiently alter the flow of dunes, a process that has continued unabated for countless eons?

Humans have tried various approaches over the years to doing just that, from putting up fences to planting vegetation. But those strategies have limitations, and some can even be counterproductive. McNamara, Vriend and their colleagues want to use their knowledge of dune dynamics to improve the process.

Earlier this year, McNamara traveled to Chile where she joined researchers led by Tomás Trewhela at the Universidad Adolfo Ibañez. They worked on sand dunes around Viña del Mar, a community on the Pacific Ocean. The team planted several large obstacles, including poles with arms made from pool noodles, into the dune. The group is now monitoring the experiment to investigate how various obstacles may aggravate or stall sand transport.

Vriend is currently reinstalling the circular flume in her lab on the ɫ��ֱ�� campus—an infrastructural challenge since the machine weighs 400 pounds.

“Can we actually affect where a dune is going to migrate?” McNamara said. “What happens if we have a dune, and we put rocks in front of it, for example?”

The graduate student saw first-hand why questions like these are so important during a research trip in June to the Indonesian island of Java. There, she met people whose lives had been overturned by geological disasters, including residents who had lost their homes to repeated flooding.

“The human impact is what drives my research,” McNamara said. “It’s really going to stick with me—talking to these families and seeing where they’re living, hearing about the impossible decisions they have to make.”

Across the globe, deserts are spreading, engulfing homes, roads and even entire villages in sand. Engineers at ɫ��ֱ�� are exploring how humans can shift the paths of these towering formations.

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Which tree species are best at cooling down the city?

Megan Maneval — Thu, 14 Aug 2025 20:04:12 +0000

Which tree species are best at cooling down the city? Megan Maneval Thu, 08/14/2025 - 14:04

INSTAAR

INSTAAR doctoral student Advyth Ramachandran is presenting preliminary findings at a conference in Baltimore. His work seeks to understand the cooling effects of various urban tree species in ɫ��ֱ��.

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Human emissions drove the megadrought in the western US

Yvaine Ye — Thu, 14 Aug 2025 15:16:51 +0000

Human emissions drove the megadrought in the western US Yvaine Ye Thu, 08/14/2025 - 09:16

Yvaine Ye

Greenhouse gas and aerosol emissions from human activity have been driving the prolonged drought in the western United States through a complicated connection with the Pacific Ocean, according to a new ɫ��ֱ��-led study.

For more than two decades, an extreme dry spell has drained the Colorado River, devastated local farms, and intensified wildfires across the American Southwest. The new prediction, published Aug. 13 in Nature, could help water managers region develop better water use plans or invest in infrastructure accordingly, with relief potentially still decades away.

“Our results show that the drought and ocean patterns we’re seeing today are not just natural fluctuations—they’re largely driven by human activity,” said Jeremy Klavans, postdoctoral researcher in ɫ��ֱ��’s Department of Atmospheric and Oceanic Sciences and lead author of the study.

Worst drought in 12 centuries

The water level of Lake Mead on the Colorado River dropped to about a third of its total capacity in 2021 and reached the lowest point in the lake’s history in 2023. (Credit: European Union, Copernicus Sentinel-2 Imagery)

The drought hitting the Colorado River Basin states and California is directly linked to a climate pattern of the north Pacific Ocean, known as the Pacific decadal oscillation (PDO).

The PDO is a natural fluctuation of the Pacific that waxes and wanes every two decades or so. In its positive phase, waters in the eastern Pacific Ocean along the U.S. West Coast tend to be warmer, whereas waters near Japan are colder. In its negative phase, the pattern flips, bringing cold water to the eastern Pacific.

Since the 1990s, the PDO has been stuck in a negative phase, an unusually long stretch for a typical cycle, Klavans said.

That has had profound impacts on the United States. The cold air and water along the U.S. West Coast hold less moisture than warm air, causing a reduction in precipitation. This extended cool phase also pushed storms that would have brought water to the region farther north.

As a result, scientists estimated that about 93% of the western United States is experiencing drought, with 70% facing severe dry conditions. Prior studies have shown that the past two decades have been the driest in the American Southwest in at least 1,200 years.

Scientists had long thought that the PDO was entirely determined by natural forces, such as the heat exchanges between the ocean and the air. Even the latest report from the Intergovernmental Panel on Climate Change (IPCC), a body of experts convened by the United Nations, said the PDO is controlled by natural forces with high confidence.

If that theory was correct, the PDO should have flipped from negative to positive in 2015 after a strong El Niño event warmed the Pacific.

Instead, the PDO shifted positive for a short time following the El Niño before reverting to the negative phase again.

New reality

To understand why the PDO has been stuck, Klavans and his team used a large collection of climate simulation programs to predict what would happen in the future.

Using a new suite of over 570 simulations, the team found that between 1870 and 1950, changes in the PDO were almost entirely driven by internal forces. But since the mid-20th century, greenhouse gas and aerosol emissions have accounted for more than half of the variations in the PDO.

The team discovered that existing climate models tend to overestimate the role of internal factors on the PDO while underestimating the influence of external factors, such as emissions. After correcting the imbalance, the team found that emissions, and their impacts on the PDO, have been responsible for nearly all of the precipitation decline in the western United States over the past three decades.

“People have been trying for a long time to find out why this part of the country is so dry, and we have an answer for that finally,” Klavans said.

Because the same imbalance has been shown in other regions, Klavans said the study’s implications could go far beyond the Pacific. For example, the North Atlantic Oscillation, a similar fluctuation over the Atlantic Ocean, is driving drought in places like Spain. He added that improving climate models to capture the role of external forces could help scientists predict future changes in precipitation across the globe.

As for the American Southwest, the outlook is grim. If greenhouse gas emissions continue to rise, the PDO will likely remain in its negative phase, and the drought will persist for at least the next three decades, Klavans said.

“With this information, water planners could set new expectations and make proper investments in water infrastructure now, knowing this drought is here to stay,” Klavans said.

For example, some Californian cities are already building desalination plants to turn seawater into drinking water.

“This study can allow us to better quantify the costs of continued greenhouse gas emissions for Americans,” Klavans said. “That can only help our region plan for a better future.”

New research revealed that changes in the Pacific Ocean are driving the unrelenting dry spell in the American Southwest, and it might not let up for the next three decades.

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The water level of the Reflection Canyon, a section of the Colorado River, was extremely low in 2021. (Credit: Jay Huang/Flickr)

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The water level of the Reflection Canyon, a section of the Colorado River, was extremely low in 2021. (Credit: Jay Huang/Flickr)

New report evaluates how we can use energy better in buildings at a community scale

Megan Maneval — Mon, 11 Aug 2025 14:43:17 +0000

New report evaluates how we can use energy better in buildings at a community scale Megan Maneval Mon, 08/11/2025 - 08:43

RASEI Fellow Gregor Henze is a co-author and co-editor on a new report from the International Energy Agency evaluating approaches aiming to use energy more efficiently in buildings and districts.

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Air pollution and warming are changing Colorado's remote alpine lakes

Megan Maneval — Thu, 07 Aug 2025 15:01:21 +0000

Air pollution and warming are changing Colorado's remote alpine lakes Megan Maneval Thu, 08/07/2025 - 09:01

INSTAAR

The Oleksy lab has taken over a 42-year-old monitoring project in Rocky Mountain National Park. The lab's investigations reveal how remote alpine watersheds are changing in the Anthropocene.

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Historical practices led to pollution disparities in Denver

Megan Maneval — Wed, 30 Jul 2025 19:23:53 +0000

Historical practices led to pollution disparities in Denver Megan Maneval Wed, 07/30/2025 - 13:23

New work, led by former CIRES and ɫ��ֱ�� doctoral student Alex Bradley, shows that modern pollution patterns and the burdens they place on communities in Denver depend heavily on historical changes, including city planning, industry and discriminatory redlining practices.

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Rainy tropics could face unprecedented droughts as an Atlantic current slows

Yvaine Ye — Wed, 30 Jul 2025 15:00:00 +0000

Rainy tropics could face unprecedented droughts as an Atlantic current slows Yvaine Ye Wed, 07/30/2025 - 09:00

Yvaine Ye

Some of the rainiest places on Earth could see their annual precipitation nearly halved if climate change continues to alter the way ocean water moves around the globe.

In a new ɫ��ֱ��-led study published July 30 in Nature, scientists revealed that even a modest slowdown of a major Atlantic Ocean current could dry out rainforests, threaten vulnerable ecosystems and upend livelihoods across the tropics.

“That’s a stunning risk we now understand much better,” said lead author Pedro DiNezio, associate professor in ɫ��ֱ��’s Department of Atmospheric and Oceanic Sciences, adding that parts of the Amazon rainforest could see up to a 40% reduction in annual precipitation.

The AMOC makes up half of the global thermohaline circulation, a large, conveyor belt–like ocean current system driven by temperature and salinity. (Credit: Avsa/Wikimedia)

The ocean conveyor belt

The Atlantic Meridional Overturning Circulation (AMOC) is a massive system of ocean currents that moves water through the Atlantic Ocean, transporting warm, salty water from the tropics to the North Atlantic. The AMOC plays an important role in regulating the climate by redistributing heat from the southern to the northern hemisphere. It also makes sure the tropical rain belt, a narrow band of heavy precipitation near the equator, stays north of it.

As the climate warms, melting polar ice and increasing rainfall will dilute the ocean’s surface waters, making them less dense and potentially slowing down the circulation. The impact of a weakened AMOC on the tropics remains uncertain, because scientists have only been monitoring the system directly for two decades.

As a technician at a National Oceanic and Atmospheric Administration (NOAA) lab in Miami in 2005, DiNezio helped calibrate some of the earliest measurements of AMOC. At the time, he had no idea that he’d be studying that very same system two decades later.

“A few years ago, this monitoring system recorded signs of a decline in the AMOC, but it later rebounded. So we weren’t sure if it was just a fluke. The problem is, we haven’t been measuring the ocean long enough to detect meaningful long-term change,” DiNezio said.

While scientists are uncertain whether the AMOC has already begun to decline, climate models predict the system will eventually weaken because of climate change.

Predicting the future

DiNezio and his team set out to explore how a future slowing of these critical ocean currents could impact global precipitation patterns.

“Changes in rainfall are very difficult to predict, because so many factors are involved in making rain, like moisture, temperature, wind and clouds. Many models struggle to predict how the pattern will change in a warming world,” DiNezio said.

Pedro DiNezio

The team turned to climate records from about 17,000 years ago, when the AMOC last slowed down significantly due to natural causes. Evidence of precipitation preserved in cave formations, as well as lake and ocean sediments revealed how rainfall patterns responded to the slowdown during that period.

Drawing on that data, DiNezio’s team identified the computer models that best captured those ancient rainfall shifts and used them to predict how the patterns could change in the future.

Their best models predict that as the AMOC weakens and cools the northern Atlantic, this temperature drop would spread toward the tropical Atlantic and into the Caribbean. This change, on top of rising global temperatures, will lead to significant reductions in precipitation over Central America, the Amazon, and West Africa.

“This is bad news, because we have these very important ecosystems in the Amazon,” said DiNezio. The Amazon rainforest contains almost two years of global carbon emissions, making it a major carbon sink on Earth. “Drought in this region could release vast amounts of carbon back into the atmosphere, forming a vicious loop that could make climate change worse.”

While DiNezio said the AMOC is unlikely to stop completely, even a small reduction in its strength could lead to changes across the entire tropical region, increasing the risk of reaching a tipping point. But how fast and how much it slows depends on the degree of future climate change.

“We still have time, but we need to rapidly decarbonize the economy and make green technologies widely available to everyone in the world. The best way to get out of a hole is to stop digging,” DiNezio said.

Beyond the story

Our sustainability impact by the numbers:

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New research warns that global rainfall patterns could shift dramatically as a result of climate change.

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The Amazon rainforest along the Urubu River in Amazonas State, Brazil. (Credit: Andre Deak/Flickr)

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The Amazon rainforest along the Urubu River in Amazonas State, Brazil. (Credit: Andre Deak/Flickr)

Report paints grim picture of how nuclear war could impact oceans

Yvaine Ye — Mon, 28 Jul 2025 13:00:00 +0000

Report paints grim picture of how nuclear war could impact oceans Yvaine Ye Mon, 07/28/2025 - 07:00

Yvaine Ye

Recent conflicts in Europe and the Middle East have reignited fears about the use of nuclear weapons. What would a nuclear conflict do to the planet’s environment today?

In a new congressionally mandated report, oceanographer Nicole Lovenduski, who directs ɫ��ֱ��’s Institute of Arctic and Alpine Research (INSTAAR), outlined the dangerous fallout a nuclear war could bring, from firestorms and global cooling to ecosystem collapse and potentially irreversible ocean disruption.

Nicole Lovenduski/ɫ��ֱ��

“The ocean makes up three-quarters of our planet's surface,” said Lovenduski, a professor in the Department of Atmospheric and Oceanic Sciences. “Knowing how the ocean responds to changes in the environment is really important, because it can influence the global climate system.”

To date, the only use of nuclear weapons in conflict occurred in 1945, when the United States dropped two atomic bombs on Japan. At the time, scientists were not tracking the environmental impact.

According to Lovenduski’s previous research, nine nations possess more than 13,000 nuclear weapons in the world, with the United States and Russia controlling the most operational nuclear weapons. The stockpiles in countries including India, Pakistan, China, and North Korea have also increased in the past eight decades.

Compiled by dozens of scientists across the country, the report aims to reevaluate the long-term environmental impacts of nuclear war using the latest scientific evidence.

“What we learned in writing the report was that we need additional scientific research to adequately describe the potential environmental and climate consequences of a nuclear conflict. But we know enough to know that a nuclear war would be a horrific outcome for humanity,” Lovenduski said.

ɫ��ֱ�� Today sat down with Lovenduski to discuss how a nuclear conflict could change the ocean and why those changes are important.

What happens when a nuclear weapon is detonated?

Hypothetically, if there were to be a large-scale nuclear conflict on this planet that starts a lot of fire, there could be a firestorm that releases a lot of soot into the atmosphere. If it makes it all the way up into the stratosphere, where the air flow tends to be more stable, soot can stay there for a really long time and encapsulate the entire planet. That will lead to a dramatic reduction in the amount of sunlight that comes into our planet.

Without sunlight, we cannot have photosynthesis. Photosynthetic organisms, like plants on land and algae in the ocean, form the base of the food web for everything else. Without photosynthesis, we cannot have a source of food.

What would happen to the ocean, specifically?

If a lot of soot gets up into the stratosphere and blocks sunlight, it would cool the planet suddenly and significantly. That's where the concept of nuclear winter first arose many decades ago.

Sea ice could extend all the way down to places in the Pacific and Atlantic that don't currently have ice. That would affect how ocean currents move and whether surface seawater can sink and slow down large-scale circulation.

We may no longer have, for example, the Gulf Stream, bringing warm water northwards into the Atlantic, resulting in dramatic cooling of Northern Europe. Ocean currents are important in making sure many parts of the world are habitable for many.

Would people living far from coastal zones be impacted?

As a result of nuclear winter, crops on land could fail. We might look to the ocean for a source of food. But if the fish don’t have anything to eat, we’re all going to starve. So even if there's a conflict, and it doesn't affect us directly where we live, the global population is at risk of starvation.

How long would it take for the ocean to recover?

The atmosphere moves pretty fast. If the soot above the Middle East enters the stratosphere, it can spread globally within one to two years.

But the ocean moves really slowly. When water sinks in the North Atlantic, it can take hundreds, if not thousands, of years for that water to reemerge. So if you perturb the ocean, it can take a long time to recover. In some of the computer simulations we did, the simulation stopped before we even saw that recovery happen, because we were out of computing time. So we never saw the ocean recover in our simulations, which is scary.

I hope we don't ever go down this road. I hope that the people in charge of deciding whether or not to engage in nuclear conflict can learn from some of the work that we have done. I hope that the report leads to a world where there is no nuclear conflict.

ɫ��ֱ�� Today regularly publishes Q&As with our faculty members weighing in on news topics through the lens of their scholarly expertise and research/creative work. The responses here reflect the knowledge and interpretations of the expert and should not be considered the university position on the issue. All publication content is subject to edits for clarity, brevity and university style guidelines.

A new congressionally mandated report by a CU oceanographer warns that the use of nuclear weapons could collapse ocean ecosystems, trigger global climate disruptions and put billions at risk of starvation.

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Mushroom cloud above Nagasaki after atomic bombing on August 9, 1945. (Credit: Charles Levy/Wikimedia)

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Mushroom cloud above Nagasaki after atomic bombing on August 9, 1945. (Credit: Charles Levy/Wikimedia)

Where does your food come from? First-of-a-kind map tracks journey across thousands of miles

Yvaine Ye — Thu, 24 Jul 2025 16:17:42 +0000

Where does your food come from? First-of-a-kind map tracks journey across thousands of miles Yvaine Ye Thu, 07/24/2025 - 10:17

Yvaine Ye

If extreme rainfall wiped out all food growing in Jalisco, a Pacific coastal state in western Mexico, it would eliminate enough calories to feed 765,000 people in the United States. A widespread drought in the Brazilian state of Paraná could cut enough fat to meet needs of more than 1.7 million people in Egypt. Western Australia’s next major heatwave could knock out enough protein to feed 8 million people in China.

These are some of many insights revealed by a newly launched interactive tool called the Global Food Twin. Developed by ɫ��ֱ�� data scientist Zia Mehrabi and his collaborators at Earth Genome, a non-profit organization, the interactive digital map shows how food moves from farm to table. It offers a first-of-its kind view into the world’s highly connected and increasingly fragile food system.

Explore the global food twin

“This is a landmark effort, because no one’s ever done this at this scale and level of detail,” said Mehrabi, assistant professor of environmental studies and founder of ɫ��ֱ��’s Better Planet Laboratory, which leverages data science to address some of the leading global environmental and human rights issues. “We’re able to represent the complexity of our food system, showing people a window into a world they haven’t seen before.”

As climate change continues to put pressure on global food production and supply chains, the team hopes the data could help countries better anticipate and prepare for disruptions like droughts and floods, ensuring communities maintain food access in the face of hazards.

Food hubs

The team built the map using data on agricultural yields of common foods—including grains, meats and vegetables. They also accounted for consumer demand, trade records, transportation networks, and satellite ship-tracking data from around the world.

With the Global Food Twin, users can look up how common agricultural food groups, from grains to oil to fresh produce, travel from where they’re produced to consumers in more than 3,700 states and provinces across 240 countries. The team also calculated the calories and essential nutrients, such as protein and iron, that flow through the trades.

Zia Mehrabi (Credit: Patrick Campbell/ɫ��ֱ��)

The map is an expansion on Mehrabi’s pioneering project visualizing the U.S. food system. It revealed that just 5.5% of U.S. counties produce half of the nation’s crops.

The global version paints a similar picture. Only 1.2% of sub-national administrative units, such as states, provinces and districts, supply 50% of the world’s grains.

For example, India’s Uttar Pradesh supplies 17 gigatons of grains annually. Together with other food products the state grows, Uttar Pradesh alone provides enough calories for more than 22 million people, including close to half a million in the United States.

“Many people think the U.S. can stand alone when it comes to food supply, and we can call the shots on trade agreement. But this map illustrates that even a powerhouse like the U.S. relies heavily on imports,” Mehrabi said, adding that many food items that Americans enjoy daily almost all come from other countries.

Take bananas. Almost every banana in U.S. grocery stores comes from countries like Guatemala, Ecuador and Mexico. Coffee, aside from a small amount grown in Hawaii, mainly comes from Brazil, Colombia and Vietnam.

“This map shows very clearly how connected we are with each other when it comes to food, something many consumers don’t think about when they’re eating a banana,” Mehrabi said.

Choke points

The map also highlights the growing vulnerability of global food systems to climate change. Many critical trade corridors, such as the Mississippi River and the Rhine River in Europe, have experienced low water levels this summer, stranding ships and disrupting food transportation.

Certain globally traded crops are also under threat. Studies estimate that by 2080, rising temperature, extreme weather and climate-related pests could slash the areas suitable for growing bananas by 60%. Climate change could also reduce coffee yields in the Americas by 70%.

Mehrabi said the Global Food Twin enables researchers and policymakers to model the impact of these climate hazards on the food system.

“If, say a heatwave hit the Midwest and, at the same time, the Mississippi River slowed because of drought, where are the communities that would feel the biggest impact? We haven’t really been able to track how disruptions could ripple through the food system until now. This dataset lets us start asking those questions,” Mehrabi said.

He added that low-income households already facing food insecurity are the most vulnerable to production or supply chain disruptions, because even small shocks in the system can trigger dramatic food price spikes.

When food prices rise, policy-makers can use stimulus payments and other dignity-focused safety nets to improve purchasing power for vulnerable communities, according to Mehrabi.

“This is a critical window into how climate change can collide with trade infrastructure, labor needs and food production. For the first time, we can start visualizing how that plays out on a global scale,” Mehrabi said.

A new interactive tool exposes the fragile, interconnected web of global food trade—and how climate change could disrupt it.

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CUriosity: In the wake of Texas floods, how do emergency alerts work, and where do they fall short?

Daniel William Strain — Tue, 22 Jul 2025 16:37:06 +0000

CUriosity: In the wake of Texas floods, how do emergency alerts work, and where do they fall short? Daniel William… Tue, 07/22/2025 - 10:37

Daniel Strain

In CUriosity, experts across the ɫ��ֱ�� campus answer pressing questions about humans, our planet and the universe beyond.

This week, Carson MacPherson-Krutsky, a research associate at the Natural Hazards Center at the ɫ��ֱ��, answers: “How do emergency alerts work, and where do they fall short?”

Aftermath of the deadly flooding that devastated Central Texas in July 2025. (Credit: CC photo by World Central Kitchen via Flickr)

In the early hours of July 4, flash floods rose through parts of Texas’ Kerr County and surrounding regions, killing more than 130 people, including 27 children and counselors at a local summer camp.

In the wake of the disaster, numerous media reports raised questions about whether residents had enough warning to make it to safety.

Carson MacPherson-Krutsky knows how important timely emergency alerts are for people in the path of natural hazards like floods, wildfires, tornadoes and more. She’s a research associate in the Natural Hazards Center at ɫ��ֱ�� and has investigated emergency alert systems in Colorado. Simply put, she said: They’re all over the place.

Carson MacPherson-Krutsky

“The biggest takeaway is that it’s complicated,” said MacPherson-Krutsky, a geologist and social scientist by training who studies how to communicate risk and help people prepare for natural disasters. “There are multiple systems at work, and they vary from municipality to municipality.”

In a report published in 2024, MacPherson-Krutsky and her colleagues surveyed 222 officials from 57 of Colorado’s 64 counties about their emergency alert systems. The research was funded through a bill passed by the state legislature.

One of the most basic kinds of disaster warnings, she said, are wireless emergency alerts (WEAs). These text messages go directly to the phones of people located in a particular geographic area. Amber Alerts for abducted children use the same system. (You may be familiar with the blaring beeps and vibrations that accompany these messages).

A wide range of government groups, both local and national, can send out WEAs in the event of natural disasters or acts of violence. Personnel need to take a training, and they work through a system administered by the U.S. Federal Emergency Management Agency (FEMA) and its partners.

Before dawn on July 4, for example, the National Weather Service (NWS), which is part of the U.S. National Oceanic and Atmospheric Administration (NOAA), sent out several such text alerts. According to The Texas Tribune, one alert at 4:03 a.m. local time urged recipients to “SEEK HIGHER GROUND NOW!”

Beyond WEAs, alerts get more complicated.

In Colorado, for example, every county tends to have its own alert system, which can be managed by a wide range of groups—from sheriff’s offices to fire departments and 911 call centers. They may send out warnings over text messages, social media, TV and radio, word of mouth or even sirens. In many cases, residents have to sign up or download an app to receive messages.

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“Depending on who's sending the alert, they have different procedures and protocols in place for what triggers an alert, who sends it, what approvals are needed and so on,” MacPherson-Krutsky said.

Those disparities become especially glaring for people with disabilities or who speak languages other than English, MacPherson-Krutsky added. Currently, the WEA technology can only support messages in English and Spanish. The federal government has made moves to expand the languages available, but she noted that a recent executive order from the Trump administration could make those changes harder to enact. In Colorado, more than one-third of the emergency personnel the researchers surveyed didn’t know if their emergency alert systems had the ability to translate to other languages or alert people who are deaf.

“That creates a lot of inequity,” she said. “A deaf person living in one county might receive an alert, but their brother who lives across the border wouldn’t.”

In their report, MacPherson-Krutsky and her colleagues recommended that Colorado adopt a single, state-wide system for sending out emergency alerts. Connecticut, Florida and Oregon have such a system, which counties or other localities can use at no cost to them.

She added that federal and state funding is critical for sending timely alerts in the event of natural disasters. The White House’s proposed budget for 2026 includes a more than 25% cut in funding for NOAA.

“Natural hazards researchers are worried about what these cuts would do to public safety,” MacPherson-Krutsky said. “Our colleagues at NOAA and the National Weather Service are doing such amazing work to make these warnings better. And if some of them aren’t there to advance this research, we’ll all bear the consequences of that.”

When natural disasters strike, people across the United States often depend on timely warnings to get to safety. But in Colorado and many parts of the country, these alerts are a patchwork that vary from county to county.

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