A groundbreaking new study has identified a critical upstream driver behind some of the most punishing heat and dryness events in the American Southwest: parched soils in northern Mexico. When the region’s land dries out, the lack of moisture appears to trigger chain reactions that send scorching temperatures and prolonged drought conditions sweeping hundreds of miles north into Arizona, New Mexico, and Texas creating what scientists call “hot droughts.” Published in the journal Geophysical Research Letters, the research emphasizes that these compound events where extreme heat and prolonged dryness overlap should be treated with the same urgency as hurricanes, complete with early warnings, public alerts, and targeted preparedness measures.

When Heat Meets Drought

The study defines a hot drought as a period of at least two weeks of unusually low rainfall combined with three or more consecutive days of abnormally high temperatures. In such events, heat and dryness reinforce each other in a destructive feedback loop. As soil moisture evaporates, it cools the surface and atmosphere. But when the ground is dry, that natural cooling fails. Instead, more solar energy turns directly into heat, raising air temperatures and intensifying the drought.

“The combination of dry soils and persistent heat is a dangerous cycle that can propagate across large regions,” explained Enrique Vivoni, hydrologist at Arizona State University and senior author of the study. “Hot droughts will move beyond borders and impact health, infrastructure, and daily life. We need early alert systems for hot droughts just like we have for hurricanes.”

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The Record-Breaking Heat of 2023

The research team analyzed climate data from the summer of 2023, one of the hottest and driest periods ever recorded in the region. During this time, average daytime temperatures in parts of the Southwest soared 8°C (14°F) above normal, while rainfall plummeted amid a weakened North American monsoon. Using data from weather stations, rain gauges, and a 40-year soil moisture record, the team found that 2023’s hot drought was nearly five times more severe than the average since 1980.

“This kind of event is self-reinforcing,” said Somnath Mondal, a hydroclimatologist at Northeastern University and co-author of the study. “Lack of rainfall increases heat, and that heat in turn dries the soil further, it’s a vicious cycle that feeds on itself.”

Heat Born in Mexico, Carried Northward

One of the study’s most striking findings is the clear cross-border linkage between soil conditions in northern Mexico and extreme weather in the U.S. Southwest. In normal monsoon years, rainfall over Mexico’s mountains and valleys evaporates back into the air, replenishing moisture that eventually forms clouds and rain downwind across the United States. But in 2023, those Mexican soils were too dry to supply moisture. The resulting “moisture shortfall” disrupted the entire regional water cycle. As dry winds moved north, they effectively exported Mexico’s drought into neighboring U.S. states.

“In 2023, Mexico’s dry soils influenced Arizona’s hot drought even more strongly than Arizona’s own soil,” said Mondal. “It’s a powerful reminder that climate systems don’t stop at national borders.” Vivoni added, “We’ve long known that we receive water vapor and rainfall from Mexico. What we didn’t realize until now is that we can also receive a hot drought.”

When the Nights Refuse to Cool

The study also found that 2023’s extreme heat persisted well into the night. Normally, desert regions cool rapidly after sunset as the ground radiates stored heat back into space. But during the hot drought, overnight temperatures stayed unusually high.

“The heat was so intense during the day that the land couldn’t fully cool off at night,” Vivoni said. “That residual warmth built up day after day, keeping temperatures elevated 24 hours a day.”

This nocturnal heat retention, observed even in rural areas, has become increasingly common over the past four decades. The consequences are severe: when nights remain hot, people’s bodies cannot recover from daytime stress, leading to rising rates of heat exhaustion, heat stroke, and mortality especially among outdoor workers, children, and the elderly.

“There isn’t enough public understanding that a hot drought is more dangerous than a typical heat wave,” Vivoni warned. “You need to take more precautions both for people and infrastructure.”

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Toward Forecasts and Early Warnings

The authors argue that their findings should inform new systems for monitoring and forecasting hot droughts. By tracking soil moisture in upwind regions such as northern Mexico, meteorologists could identify early warning signs of extreme conditions likely to hit the U.S. Southwest days or even weeks in advance. Such alerts could enable public health agencies to prepare cooling centers, utilities to manage power demand, fire departments to boost readiness, and employers to limit outdoor work hours during dangerous periods.

“Hot drought alerts wouldn’t replace heat advisories or drought monitors,” Vivoni said. “They would connect the dots showing where heat and dryness overlap, and where the risk of sustained, compounding impacts is highest.”

Modeling the Future of Hot Droughts

Looking ahead, the researchers plan to use atmospheric and land-surface models to better simulate how hot droughts evolve and spread. They aim to determine whether similar “teleconnections” exist in other regions influenced by monsoon systems, such as South Asia or Sub-Saharan Africa.

“As the planet warms, more regions will experience the kind of soil drying that fuels hot droughts,” the authors wrote. “The 2023 event shows how quickly these conditions can cascade across borders and ecosystems.”

Ultimately, the findings underscore a broader truth about climate change: no region exists in isolation. Drought and heat waves that begin in one country can ripple across entire continents through shared airflows and soil-atmosphere feedbacks.

“Climate doesn’t recognize national boundaries,” Vivoni concluded. “We are more interconnected than we thought and that means our solutions must be, too.”

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