Thirstwaves: The hidden climate threat drying out American farms

As climate change accelerates, most people think of rising temperatures, melting ice caps, and stronger storms. But there’s another silent force growing stronger in the background – one that directly threatens food systems. The air itself is becoming thirstier.

This atmospheric thirst is not about how dry it feels. It’s about how much water the air can pull from the land, even when there’s no drought in sight. Scientists call this “evaporative demand,” and it’s emerging as a powerful driver of crop stress, water loss, and agricultural uncertainty.

Recent research by M. S. Kukal of the University of Idaho and M. Hobbins of the University of Colorado and the National Oceanic and Atmospheric Administration (NOAA) has identified a dangerous pattern.

As global temperatures rise, extreme events of evaporative demand are not only increasing – they’re changing where and how they strike. The authors have given these intense events a name: thirstwaves.

When the air demands too much

A thirstwave isn’t just a hot spell. It’s a multi-day period where the atmosphere pulls moisture from the land with extraordinary force.

Kukal and Hobbins define it precisely: a thirstwave occurs when the standardized short-crop evapotranspiration (ETos) exceeds the 90th percentile for at least three consecutive days.

“A thirstwave is a period of extremely high evaporative demand that, like its cousin the heat wave, can wreak havoc on a growing season.” noted the researchers.

This definition mirrors how meteorologists define heatwaves but centers on a different metric. Instead of just temperature, ETos includes radiation, humidity, and wind – factors that dramatically impact water loss from crops.

That makes thirstwaves a uniquely agricultural stressor, invisible to people but devastating to plants.

Measuring the invisible

ETos is calculated based on how much water would evaporate from a well-watered, short grass surface under local weather conditions. It captures the “potential” for water to move from soil and plant surfaces into the atmosphere.

During a thirstwave, the atmosphere essentially goes into overdrive, demanding more moisture than usual. From 1981 to 2021, thirstwaves across the United States averaged 0.8 millimeters per day above normal, lasted about 4 days, and occurred nearly 3 times per growing season.

Some places saw much worse. One thirstwave stretched to 17 days. Another county experienced 20 thirstwaves in one season. The High Plains recorded the most intense thirstwaves. Longer events appeared frequently across the South, Upper Midwest, Pacific Northwest, and West Coast.

Geography of a growing crisis

One of the most surprising findings in the study is that thirstwaves don’t align with regions that usually have the highest overall evaporative demand. While the Southwest often leads in seasonal ETos, thirstwave intensity and frequency follow different paths.

Places like the Prairie Gateway and Mississippi Portal now lead in thirstwave severity. That shift means farmers in new regions are facing environmental conditions they weren’t prepared for a generation ago.

The High Plains suffer some of the most intense thirstwaves, often exceeding 1 mm per day above the norm. Meanwhile, counties in the South and West Coast report the most frequent events.

This mismatch between long-term averages and extreme conditions shows why thirstwave-specific metrics are essential for future planning.

Thirstwaves are getting worse

Trends over four decades show a clear and concerning trajectory. Nationwide, thirstwave intensity rose by 0.06 mm/day per decade. Duration increased by 0.10 days, and frequency climbed by 0.39 events per decade.

But the worst-affected regions show even sharper increases. Prairie Gateway stands out with the steepest trend in intensity at 0.13 mm/day per decade. It also leads in frequency with 0.60 more events per decade. These changes make it one of the most vulnerable zones for thirstwave impacts.

The Mississippi Portal region saw the longest increases in event duration, rising by 0.17 days per decade. In Southern Seaboard and Fruitful Rim, nearly half the cropland now faces significantly more frequent thirstwaves.

Revisiting an infamous drought

The thirstwave framework gives new insight into one of America’s most infamous droughts. The 2012 drought devastated crops, especially in the Midwest. But now, Kukal and Hobbins show that it also marked the peak of thirstwave severity across much of the nation.

In that year alone, thirstwave intensity across croplands hit 1.32 mm/day – almost twice the long-term average. Events lasted 5.8 days and occurred 8.5 times during the growing season. These values were far above normal, reaching up to 2.8 times the usual frequency in some places.

“2012 demonstrated the most severe thirstwaves observed in CONUS when represented by any of the three characteristics.” added M. S. Kukal and M. Hobbins.

The 2011–2012 period accounted for the worst thirstwaves on record in nearly half of all U.S. cropland, based on at least one characteristic: intensity, duration, or frequency. This reanalysis confirms that what we saw in those years was not just heat – it was extreme atmospheric thirst.

Few places are safe from thirstwaves

Historically, some counties never faced a thirstwave in a given year. That’s no longer the case. In the 1980s, up to 41% of counties went an entire season without one. But by 2021, that number dropped sharply.

The probability of escaping a thirstwave during the growing season has declined by about 4% each decade. Areas like the Northern Plains and Northern Rockies – once rarely affected – now face at least one thirstwave almost every year.

This means more widespread exposure to crop stress, especially for rainfed farming systems that can’t compensate with irrigation.

Why thirstwaves matter more than heatwaves

Heatwaves dominate climate headlines, but they only tell part of the story. Thirstwaves better capture how extreme weather stresses vegetation. That’s because temperature alone doesn’t drive evapotranspiration. Radiation, wind, and humidity all play major roles.

For example, a warm but humid day may feel intense but poses less risk to crops than a breezy, dry, and sunny one. That second scenario can pull water from leaves and soil at alarming rates – especially when it lasts for days.

By using ETos, thirstwaves provide a broader lens. They explain why crops wilt, why irrigation falls short, and why yields drop even when rainfall is average.

Identifying thirstwaves earlier

Kukal and Hobbins argue that farmers, water managers, and policymakers need tools to monitor thirstwaves in real time. Most irrigation systems were designed for past climate norms. They’re not built for long, repeated peaks in atmospheric demand.

“Continuing to measure and track thirstwaves will be crucial for crop and water management in the coming years, especially as the climate continues to warm,” the researchers noted.

Regions with shallow aquifers or restricted surface water rights may struggle the most. Even farmers with irrigation may not keep up if their systems can’t meet daily peak demand.

By identifying thirstwaves early, we can adapt farm practices, improve irrigation scheduling, and plan for more resilient agriculture. It won’t stop the air from getting thirstier – but it may help crops survive the heat.

The study is published in the journal Earth’s Future.

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