Thursday, September 29, 2022

How do floods in Kentucky and droughts at Lake Mead happen at the same time?

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Shreya Christina
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On Monday, President Joe Biden heeft flew to Eastern Kentucky to visit families affected by historical flood which hit the Midwest in late July and early August, at least 35 dead and hundreds missing. “It will take some time to get through this, but I promise you we won’t leave,” Biden said. “We’ll stay here while it lasts.”

About 2,000 miles away, the water was in Lake Mead – the largest reservoir in the country and a crucial water source for millions of people in the West – at a historic low, exacerbating a drought now in its third year. Part of the country has too much water; another has too little. These two things are related. They were also expected.

“This has been a slow-motion crisis for two decades,” said Michael Crimmins, a climatologist at the University of Arizona. “It’s just coming together right now.”

The short answer to why these seemingly opposite things happen at once is that climate change is making our atmosphere thirstier. Or, in more scientific terms, as the Earth warms, the atmosphere can hold more water vapor. This is happening at an exponential rate: the math behind the napkin is that the atmosphere can store about 7 percent more water per degree Celsius of warming, and we are currently at about 1.2°C above pre-industrial temperatures. The result is an atmosphere that takes longer to become saturated with water, which means fewer downpours, but when they do occur, those storms dump more water at once, resulting in flooding.

Paradoxically, our changing atmosphere is also a perfect recipe for drought. Higher temperatures mean water evaporates faster, and when it falls, it’s less likely to fall like the snow that historically fed many of the rivers and streams of the American West. The rain isn’t very helpful either, as the elimination of a drought requires a combination of snowfall and long, sustained rainy seasons rather than short, extreme eruptions.

“The water infrastructure in the West is built around a layer of snow,” said Noah Diffenbaugh, a climate scientist at Stanford University. “It doesn’t need to be stored in a reservoir if it’s stored in the snowdrift.” Reservoirs have limited capacity, Diffenbaugh noted, so if an extreme rainstorm were to fill a reservoir above capacity, that water — which would otherwise have fallen as snow or over an extended period of time — would have to be released.

Water levels in Lake Mead, shown on July 23, are at their lowest level since the reservoir was first filled in April 1937.
Frederic J. Brown/AFP via Getty Images

Instead, we see a vicious circle: As soil and vegetation dry up in drought-prone regions, they become susceptible to wildfires and have less water retention capacity, so when extreme rainstorms come in, they cause flooding and erosion. The heat dries up the water before it has any effect on the drought, and the erosion allows the soil to hold even less water, making the next flood a little worse. We saw this kind of mid-drought flooding just a week before the Midwestern floods, when monsoon rains swept through Flagstaff, Arizona.

“There’s a really strong negative feedback loop here,” said Bill Gutowski, a professor of meteorology at Iowa State University. “All of a sudden you get these compound effects that come into play.”

As climate change intensifies, we will see more extreme rainfall across the country and the world. We will also see more intense droughts. Basically, Crimmins said, “dry places will tend to get drier, and wet places will tend to get wetter.”

Those places can’t help each other either. The water from the west will not be dumped in the Midwest, and the flooding in the Midwest will not rejuvenate the Colorado River. Instead, the same weather patterns that once made those places attractive to move to — Midwestern precipitation has historically been great for agriculture — are amplified in ways we just weren’t prepared for.

Our built world has historically been designed around a predictable climate, and that era is over. As cafemadrid’s Umair Irfan explained in 2018, once-rare “1,000-year-old” weather events are becoming more common. “The real question is, what does it take to design and build infrastructure that will protect against flooding in a changing climate?” said Diffenbaugh. “Our assumptions are outdated.”

The answer doesn’t just lie in infrastructure. The Earth will outrun us if we don’t reduce the emissions that brought us here to begin with, and wipe out any gains we could make from engineering. On this front, there’s rare good news: The Inflation Reduction Act, passed by the Senate this week, is a monumental step in the right direction. We make our bed instead of setting it on fire. Now we must learn to adapt to it.

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