It’s not an earthquake. And it’s not the big drought. In fact it is quite the opposite. Mega flood. A new study in Science Advances shows that climate change has already doubled the chances of a catastrophic flood in California over the next four decades. And experts say it would be unlike anything anyone alive today has ever experienced. Daniel Swain, a climate scientist at UCLA and a researcher involved in the study, describes a major flood as “a very severe flooding event over a wide area that has the potential to have devastating effects on society in the affected areas.” He said a major flood is similar to the 1,000-year flood events seen this summer in the St. Louis area and Kentucky, but over a much larger area, such as the entire state of California. These massive floods, which experts say would turn California’s lowlands into a “vast inland sea,” may have previously been a once-in-a-lifetime occurrence in the state. But experts say climate change is increasing the likelihood of these catastrophic disasters, making them more likely to occur every 25 to 50 years. Climate change is adding to heavy rainfall events, causing flooding to occur more regularly, as has occurred several times this summer in Eastern Kentucky, St. Louis, and even California’s Death Valley National Park. California is prone to these atmospheric river floods of course, and major floods from them have happened in the past — but climate change is stepping up and millions of people could be affected. The study said the atmospheric rivers could become continuous for weeks, as shown in this animation. Xingying Huang, one of the authors of the study, made this loop, which depicts water vapor transport and possible precipitation accumulation at selected time segments during the 30-day scenario. The area with the most damage will be California’s Central Valley, including Sacramento, Fresno and Bakersfield, the study authors said. The Central Valley, about the size of Vermont and Massachusetts combined, produces a quarter of the nation’s food supply, according to the US Geological Survey. A flood of the size that fills this valley could be the costliest geophysical disaster to date, costing more than $1 trillion in damages and devastating low-lying areas of the state, including Los Angeles and Orange counties, the study found. That would be more than 5 times the cost of Hurricane Katrina, currently the costliest disaster in US history. “Such a flooding event in modern California would likely exceed the damage from a large-magnitude earthquake by a significant margin,” the study showed. This study is the first phase of a three-part series studying the impacts of a future megaflood event in California. The next two phases are expected to be released in two to three years. “Ultimately, one of our goals is not just to understand these events scientifically, but it’s also to help California prepare for them,” Swain said. “It’s a matter of when, not if (the big flood) will happen.” It’s happened again. It will happen again, but worse, scientists warn More than 150 years ago, a powerful series of atmospheric rivers inundated the Golden State, causing one of the most extraordinary floods in history, following a drought that had left the West parched for decades. Communities were demolished within minutes. It was the winter of 1861-1862, and a historic major flood turned the San Joaquin and Sacramento valleys into a “temporary but vast inland sea,” according to the study. Some areas had up to 30 feet of water for weeks, wiping out infrastructure, farmland and towns. Sacramento, the new state capital at the time, had been under ten feet of water for months. This 1861 photo shows flooding in Sacramento. Sacramento Public Library The disaster began in December 1861, when nearly 15 feet of snow fell in the Sierra Nevada. Recurring atmospheric rivers dropped warm rain for 43 days afterward, pouring water down the mountain slopes and valleys. Four thousand people lost their lives, a third of the state’s property was destroyed, a quarter of California’s cattle population drowned or starved, and one in eight homes was a complete loss to the flood. Additionally, a quarter of California’s economy was wiped out, resulting in statewide bankruptcy. Swain warns that a major flood like this will happen again, but worse and more frequent. “We find that climate change has already increased the risk of a megaflood (1862) scenario in California, but that future climate warming will likely produce even sharper increases in risk,” the study warns. Many of today’s large cities of millions are built right on top of ancient flood deposits, Swain added, putting many more people at risk. About 500,000 people lived in California in 1862. Now, the state’s population is over 39 million. “When this (flood) happens again, the consequences would be very different than they were in the 1860s,” Swain said. Climate change increases the amount of rain the atmosphere can hold and causes more water in the air to fall as rain, which can lead to flash floods. Both are and will continue to happen in California. The new study shows a rapid increase in the likelihood of weekly, recurring strong to extreme atmospheric rivers during the cool season. An atmospheric river is a long, narrow region of heavy moisture in the atmosphere that can transport moisture thousands of miles, like a fire hose across the sky. They typically bring beneficial rainfall to drought-prone areas like California, but could quickly become dangerous with a warming climate. Historically, these winter atmospheric rivers dump snow on the Sierra Nevada, but as the climate warms, more of the snow will fall as rain. Instead of melting slowly over time, everything rushes, accumulates and floods at once. With a neighbor like the Pacific Ocean, California has “an infinite reservoir of offshore water vapor,” Swain added. California’s mountainous terrain and fire hazard make it particularly vulnerable to flooding. Prolonged burn scars from wildfires can create a steep, smooth surface for water and debris to flow. With fires getting bigger and burning more area thanks to climate change, more areas are susceptible to these debris flows. Although models show this major flooding is inevitable, experts say there are ways to mitigate the excess loss. “I think the extent of (megaflooding) losses can be greatly reduced by doing some things to revamp our flood management and water management systems and our disaster preparedness,” Swain said. Huang, a project scientist at the National Center for Atmospheric Research and a researcher involved in the study, said everyone can do a little bit to fight climate change. “If we work together to reduce future emissions, we can also reduce the risk of extreme events,” Huang said. The-CNN-Wire& 2022 Cable News Network, Inc., a WarnerMedia company. All rights reserved.
