Where 2 Inches of Rain Can Kill You

The morning after Tropical Storm Hilary brought a deluge of rain to Death Valley National Park, the sun peeked through lingering clouds over a wet, muddy landscape. In photos shared by park officials, flood waters formed new lakes and left sections of main roads crumbling and covered in debris. The storm also caused a temporary loss in electricity and phone service in the park, and it dislodged wastewater and water pipes, compromising four utility systems.

Of course, this stretch of the California desert is no stranger to extremes. The Death Valley National Park website boasts it is the “hottest place on Earth;” just last month, the park reached 128 degrees Fahrenheit. It is also typically the driest place in North America, receiving an annual average of 2.15 inches of rain.

This year, that total will be higher, thanks to Hilary. In just one day, the park saw 2.20 inches of rain, according to one gauge reading in Furnace Creek. It’s now the rainiest day on record for the area — a record that was just reset last August after 1.7 inches of precipitation fell in the park.

Given Death Valley’s steep, low-lying topography, flooding is a well-recognized risk. In advance of the storm, the park was closed to the public. Still, officials told me Thursday an “estimated 400 residents, travelers, and employees” had to shelter in place there following the storm for about 24 hours until an exit lane could be cleared. Officials say they are still assessing the extent of the damage, a process they expect to take weeks in the 3.4 million acre park. For now, Death Valley and all roads within it remain closed indefinitely.

All because of just over two inches of rain.

For those of who do not live in a desert (which is most of the U.S. population, though the desert-dwelling population has spiked in recent years), that might seem like a minuscule amount. Someone living along the Gulf Coast who is no stranger to full-force hurricanes might dismiss two inches of rain from a tropical storm, because where they live, it wouldn’t be considered a danger. But the toll 2.20 inches of rain took on Death Valley offers an important example of how hazards interact with their surroundings to become threats or even disasters — an understanding that’s becoming increasingly important as climate change alters different region’s risk profiles.

Wherever you live, you’ve likely been faced with some type of natural hazard, whether it’s snow storms or heat waves. Depending on how at-risk your area is, there might even be infrastructure dedicated to mitigating the impact that hazard could have, like building code measures designed to withstand earthquake shaking or a siren to warn of tornadoes.

It’s not just the built environment that needs to be prepared, though — it’s also the population. To calculate the National Risk Index, the Federal Emergency Management Agency factors in the area’s infrastructure and industry, as well as the community’s social vulnerability and preparedness. All of those pieces are a part of determining how a community weathers a hazard like Tropical Storm Hilary.

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According to the World Meteorological Organization, preparedness measures like the examples I offered above and improvements in forecasting have helped reduce extreme weather disaster deaths in recent decades, even as these events occur at an increased frequency. However, experts agree that progress could be lost as climate change introduces new and heightened hazards to locales.

For example, 300 miles northwest of Death Valley in San Francisco, city officials have come to define an “extreme heat event” as any day when temperatures surpass 85 degrees. Again, it’s a forecast that might not seem threatening to anyone in the Mojave, but researchers have found that San Francisco sees an increase in the emergency department visits, hospitalizations, and mortality beyond that threshold. With a high population of residents who are unhoused and a low rate of air conditioning ownership, the city is considered particularly vulnerable to rising temperatures.

“We were not built for heat,” Mary Ellen Carroll, the executive director of the San Francisco Department of Emergency Management, said at a conference in July. “People die under those conditions because of our built environment.”

And the city is expecting a lot more of those conditions in the future, with the average number of extreme heat events expected to double in the coming decades.

Even in areas accustomed to high temperatures, climate change is pushing the boundaries of our preparations. Back in Death Valley, officials believe two deaths in the park this summer can be linked to extreme heat exposure. The temperatures on the days in question were both above 110 degrees.

So far, there have been no deaths reported in Southern California from Tropical Storm Hilary, though desert and rural mountain towns are still in the thick of determining the damage left behind. And while experts remain uncertain about the likelihood of tropical storms impacting the region in the future, flooding is expected to be an increasing hazard due to climate change. In some drought-stricken areas, this might be welcome; in others, it will require a reexamination of local infrastructure, warnings, and community preparedness.

A few inches of rainfall might not seem like much, but as Tropical Storm Hilary showed, where it falls can make all the difference.

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