Many Californians fear the “Big One,” but it might not be what you think.
It’s not an earthquake. And it isn’t the mega drought. It’s actually the exact opposite.
A megaflood.
A new study by Science Advances shows climate change has already doubled the chances of a disastrous flood happening in California in the next four decades. And experts say it would be unlike anything anyone alive today has ever experienced.
Daniel Swain, a climate scientist with UCLA and a researcher involved in the study, describes a megaflood as, “a very severe flood event across a broad region that has the potential to bring catastrophic impacts to society in the areas affected.” He said a megaflood is similar to the 1,000-year flash flood events seen this summer in the St. Louis area and Kentucky, but across a much wider area, such as the entire state of California.
These massive floods, which experts say would turn California’s lowlands into a “vast inland sea,” might have previously happened once in a lifetime in the state. But experts say climate change is increasing the likelihood of these catastrophic disasters, causing them to occur more like every 25 to 50 years.
National Park Service/AP
In this photo provided by the National Park Service, Mud Canyon Road is closed due to flash flooding in Death Valley, California.
Climate change supercharges heavy rain events, making flash floods occur more regularly, as has been noted several times this summer in Eastern Kentucky, St. Louis, and even in California’s Death Valley National Park.
California is prone to these floods from atmospheric rivers naturally, and major floods from them have happened before — but climate change is upping the ante, and millions of people could be impacted.
The study said atmospheric rivers could become consecutive for weeks on end, like seen in this animation. Xingying Huang, one of the authors of the study, made this loop, which illustrates the water vapor transportation and potential precipitation accumulation at selected time slices during the 30-day scenario.
Citizen of the Planet/UCG/Universal Images Group/Getty Images
California's Central Valley, which produces one-fourth of the nation's food, will be ravaged by a megaflood.
The area with the most destruction would be the Central Valley of California, including Sacramento, Fresno and Bakersfield, the study’s authors project. The Central Valley, roughly the size of Vermont and Massachusetts combined, produces a quarter of the nation’s food supply, according to the US Geological Survey.
A flood with the size to fill this valley has the potential to be the most expensive geophysical disaster to date, costing upwards of $1 trillion in losses and devastating the state’s lowland areas, including Los Angeles and Orange counties, according to the study.
That would be more 5 times the cost of Hurricane Katrina, the current costliest disaster in US history.
Mario Tama/Getty Images
Los Angeles and Orange counties could be devastated by a megaflood within the century.
“Such a flood event in modern California would likely exceed the damages from a large magnitude earthquake by a considerable margin,” the study showed.
This study is the first phase of a three-part series studying the effects 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 question of when rather than if (the megaflood) occurs.”
It’s happened before. It will happen again, but worse, warns scientists
Over 150 years ago, a strong series of atmospheric rivers drenched the Golden State, causing one of the most exceptional floods in history following a dry spell that had left the West parched for decades.
Communities were demolished in minutes.
It was the winter of 1861-1862 and a historic megaflood transformed 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, obliterating infrastructure, farmland, and towns.
Sacramento Public Library
This 1861 photograph shows flooding in Sacramento.
Sacramento, the new state capital at the time, was under ten feet of debris-filled water for months.
The catastrophe began in December 1861, when nearly 15 feet of snow fell in the Sierra Nevada. Repetitive atmospheric rivers dropped warm rain for 43 days thereafter, dumping water down the mountainous slopes and into the valleys.
Four thousand people lost their lives, one-third of the state’s property was destroyed, a quarter of California’s cattle population drowned or starved, and one in eight homes were a complete loss by floodwaters.
In addition, one-fourth of California’s economy was obliterated, resulting in a state-wide bankruptcy.
Swain warns a megaflood like this will happen again, but worse and more frequent.
Melina Mara/The Washington Post/Getty Images
Downtown Sacramento today, which was raised 10-15 feet after the historic floods.
“We find that climate change has already increased the risk of a (1862) megaflood scenario in California, but that future climate warming will likely bring about even sharper risk increases,” the study warns.
Many of today’s major cities with millions of residents are built directly on top of the ancient flood deposits, Swain added, putting far more people in harm’s way.
About 500,000 people lived in California in 1862. Now, the state’s population is over 39 million.
“When this (flood) occurs again, the consequences would be wildly different than they were back 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 immediate flooding. Both are and will continue to occur in California.
The new study shows a rapid increase in the likelihood of week-long, 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 in the sky. They usually bring beneficial rainfall to drought-prone regions like California but could quickly become hazardous with a warming climate.
Historically these winter atmospheric rivers dump feet of snow in the Sierra Nevada, but as climate warms, more of the snow will fall as rain. Instead of melting slowly over time, it all runs off, piles up, and floods immediately.
With a neighbor like the Pacific Ocean, California has “an infinite reservoir of water vapor offshore,” Swain added.
California’s mountainous terrain and wildfire risk make it especially vulnerable to flooding. Lingering burn scars from wildfires can create a steep, slick surface for water and debris to flow off. With wildfires becoming larger and burning more area thanks to climate change, more areas are susceptible to these debris flows.
Although models show this megaflood is inevitable, experts say there are ways to mitigate excessive loss.
“I think the extent of (megaflood) losses can be significantly reduced by doing certain sorts of things to revamp our flood management and our 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 make a small effort in combating climate change.
“If we work together to decrease future emissions, we can also reduce the risk of extreme events,” Huang said.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
ccpixx photography // Shutterstock
Climate scientists continue to prove the link between climate change and extreme weather events, from hurricanes to droughts to floods. With each new weather event comes the potential for damage to people’s homes and possessions. This is not just emotionally damaging and physically dangerous, but also comes with a steep associated financial cost.
To discover how climate-resilient construction can help to mitigate natural disasters, Stacker first determined the economic damage within the United States caused by eight types of natural disasters between 2010 and 2020, based on data compiled by Our World In Data. Economic damage data spanning 2010–20, provided by EM-DAT, is expressed as a portion of U.S. gross domestic product (GDP), provided by the World Bank.
Fortunately, some of these costs can be avoided with climate-resilient construction to mitigate natural disasters. In order to understand how different natural disasters can be better anticipated and mitigated through building strategy, we outlined various climate-resilient construction and projects being used to minimize the effects of those disasters using data from the U.S. government, design firms, and media outlets. Choosing the building location carefully and with advice from experts, universally, can help mitigate many of these natural disasters.
You may also like: Space discoveries that will blow your mind
ccpixx photography // Shutterstock
Climate scientists continue to prove the link between climate change and extreme weather events, from hurricanes to droughts to floods. With each new weather event comes the potential for damage to people’s homes and possessions. This is not just emotionally damaging and physically dangerous, but also comes with a steep associated financial cost.
To discover how climate-resilient construction can help to mitigate natural disasters, Stacker first determined the economic damage within the United States caused by eight types of natural disasters between 2010 and 2020, based on data compiled by Our World In Data. Economic damage data spanning 2010–20, provided by EM-DAT, is expressed as a portion of U.S. gross domestic product (GDP), provided by the World Bank.
Fortunately, some of these costs can be avoided with climate-resilient construction to mitigate natural disasters. In order to understand how different natural disasters can be better anticipated and mitigated through building strategy, we outlined various climate-resilient construction and projects being used to minimize the effects of those disasters using data from the U.S. government, design firms, and media outlets. Choosing the building location carefully and with advice from experts, universally, can help mitigate many of these natural disasters.
You may also like: Space discoveries that will blow your mind
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
Deni_Sugandi // Shutterstock
- Economic damages between 2010–20: 0.0002% of GDP
If you live near an active volcano, evacuating remains the most important safety measure when warned of a potential eruption. However, there are ways to construct a building to make it more resilient in the face of a volcanic eruption. As eruptions can whip up fierce winds, mostly flat roofs with a slight, 15-degree slope will be less likely to be hit by the wind. The slope will allow ash to slide off the roof. Triple roof support and using smooth materials for roofing will also help ash slide away.
Similarly, concrete structures’ natural wind resistance fares better than timber-framed buildings. Lastly, designing simpler architectural structures will leave less room for ash to settle, creating a safer environment.
Deni_Sugandi // Shutterstock
- Economic damages between 2010–20: 0.0002% of GDP
If you live near an active volcano, evacuating remains the most important safety measure when warned of a potential eruption. However, there are ways to construct a building to make it more resilient in the face of a volcanic eruption. As eruptions can whip up fierce winds, mostly flat roofs with a slight, 15-degree slope will be less likely to be hit by the wind. The slope will allow ash to slide off the roof. Triple roof support and using smooth materials for roofing will also help ash slide away.
Similarly, concrete structures’ natural wind resistance fares better than timber-framed buildings. Lastly, designing simpler architectural structures will leave less room for ash to settle, creating a safer environment.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
Canva
- Economic damages between 2010–20: 0.0004% of GDP
Following proper land-use procedures will help mitigate the impacts of landslides on your property. These procedures include avoiding building near steep slopes, close to the edges of mountains, along natural erosion valleys, and near drainage ways. The use of sandbags and retaining walls are techniques that can protect buildings from floodwaters and mud caused by landslides. In areas prone to mud and debris flow, build channels or deflection walls to redirect the flow of debris around the structure—but be sure not to direct it into someone else’s building.
In 2005, a landslide destroyed 19 homes and forced the evacuation of more than 300 homes in Bluebird Canyon in Laguna Beach, California, leading to a 2.5-year reconstruction project using clever building strategies. Beyond smarter architecture, drainage systems were installed and edges along the land were stabilized to protect against another disaster. Consulting with a geotechnical professional before building will help mitigate further damage as well.
Canva
- Economic damages between 2010–20: 0.0004% of GDP
Following proper land-use procedures will help mitigate the impacts of landslides on your property. These procedures include avoiding building near steep slopes, close to the edges of mountains, along natural erosion valleys, and near drainage ways. The use of sandbags and retaining walls are techniques that can protect buildings from floodwaters and mud caused by landslides. In areas prone to mud and debris flow, build channels or deflection walls to redirect the flow of debris around the structure—but be sure not to direct it into someone else’s building.
In 2005, a landslide destroyed 19 homes and forced the evacuation of more than 300 homes in Bluebird Canyon in Laguna Beach, California, leading to a 2.5-year reconstruction project using clever building strategies. Beyond smarter architecture, drainage systems were installed and edges along the land were stabilized to protect against another disaster. Consulting with a geotechnical professional before building will help mitigate further damage as well.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
Kurniawan Rizqi // Shutterstock
- Economic damages between 2010–20: 0.0005% of GDP
When working on a building resilient to earthquake damage, be sure to include base isolators. Conventional buildings will shake with the ground during an earthquake, and when they shake too much, structural elements can sustain heavy damage, sometimes to the point of destruction.
Base isolators act as shock absorbers between the building and the moving ground. This lets the building slide back and forth instead of shaking during an earthquake, so it will still remain upright. Layers of steel and rubber with a lead core built between the floor and the foundation will also help to isolate the building from ground motion. Steel plate wall systems can mitigate earthquake damage as well.
The Ritz-Carlton/JW Marriott hotel building in Los Angeles is the first to use an advanced steel plate shear wall system to resist earthquakes. At 54 stories tall, the hotel must be able to withstand earthquakes.
Kurniawan Rizqi // Shutterstock
- Economic damages between 2010–20: 0.0005% of GDP
When working on a building resilient to earthquake damage, be sure to include base isolators. Conventional buildings will shake with the ground during an earthquake, and when they shake too much, structural elements can sustain heavy damage, sometimes to the point of destruction.
Base isolators act as shock absorbers between the building and the moving ground. This lets the building slide back and forth instead of shaking during an earthquake, so it will still remain upright. Layers of steel and rubber with a lead core built between the floor and the foundation will also help to isolate the building from ground motion. Steel plate wall systems can mitigate earthquake damage as well.
The Ritz-Carlton/JW Marriott hotel building in Los Angeles is the first to use an advanced steel plate shear wall system to resist earthquakes. At 54 stories tall, the hotel must be able to withstand earthquakes.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
G B Hart // Shutterstock
- Economic damages between 2010–20: 0.0015% of GDP
There are a number of ways to make your home more resilient to extreme heat caused by climate change. In order to keep heat out, cover windows with drapes or shades and weather-strip windows and doors. Insulation will help keep the heat out, and window reflectors can help by reflecting heat back outside.
When possible, install window air conditioners to cool the house or building and insulate around them, so the cool air doesn’t escape and the hot air doesn’t come in. For those unable to afford the costs associated with adding these climate-resilient measures, the Low Income Home Energy Assistance Program (LIHEAP) can provide financial support.
For new constructions, passive houses may be the solution to beat increasing global temperatures. A type of housing that dates back centuries, passive houses rely on building walls, roofs, and windows with more insulation and seals, including triple-paned windows, highly insulated wall systems, and energy-efficient heat pumps. Implementing these architectural elements leads to a nearly air-tight building, reducing the amount of hot air that can enter.
G B Hart // Shutterstock
- Economic damages between 2010–20: 0.0015% of GDP
There are a number of ways to make your home more resilient to extreme heat caused by climate change. In order to keep heat out, cover windows with drapes or shades and weather-strip windows and doors. Insulation will help keep the heat out, and window reflectors can help by reflecting heat back outside.
When possible, install window air conditioners to cool the house or building and insulate around them, so the cool air doesn’t escape and the hot air doesn’t come in. For those unable to afford the costs associated with adding these climate-resilient measures, the Low Income Home Energy Assistance Program (LIHEAP) can provide financial support.
For new constructions, passive houses may be the solution to beat increasing global temperatures. A type of housing that dates back centuries, passive houses rely on building walls, roofs, and windows with more insulation and seals, including triple-paned windows, highly insulated wall systems, and energy-efficient heat pumps. Implementing these architectural elements leads to a nearly air-tight building, reducing the amount of hot air that can enter.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
Piyawat Nandeenopparit // Shutterstock
- Economic damages between 2010–20: 0.0225% of GDP
To prevent or reduce damage from flooding, there are a few elements that must be taken into account when designing a building or home. Preventing water ingress will ensure a safer structure. Constructing the building with concrete or steel with concrete protects against water entering—as both of these materials are more impervious to flooding than other materials.
Installing raised windows, doors with materials to prevent water damage, and floor guards can also protect the structure. Finally, it’s important to have a drainage system in place in case water does get in, which could be sub-floor drainage, sump pumps, and non-return valves.
You may also like: How communities are dealing with invasive species across the U.S.
Piyawat Nandeenopparit // Shutterstock
- Economic damages between 2010–20: 0.0225% of GDP
To prevent or reduce damage from flooding, there are a few elements that must be taken into account when designing a building or home. Preventing water ingress will ensure a safer structure. Constructing the building with concrete or steel with concrete protects against water entering—as both of these materials are more impervious to flooding than other materials.
Installing raised windows, doors with materials to prevent water damage, and floor guards can also protect the structure. Finally, it’s important to have a drainage system in place in case water does get in, which could be sub-floor drainage, sump pumps, and non-return valves.
You may also like: How communities are dealing with invasive species across the U.S.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
Christian Roberts-Olsen // Shutterstock
- Economic damages between 2010–20: 0.0233% of GDP
When constructing buildings and homes to avoid wildfires, choosing the right location is crucial. Ideally, construction wouldn’t take place in any danger zones, but that’s not always possible. It’s important to consider the climate, wind patterns, vegetation, and escape routes when choosing where to build.
Consider the structure itself—for example, patios are more resilient than decks. Typically, patios are made from non-flammable materials whereas decks are made from wood and can trap vegetation beneath them, which act as fuel. For similar reasons, slab-on-grade and full basement foundations provide more protection as opposed to pier foundations or crawl spaces, where vegetation and other flammable debris can accumulate. Building a house from concrete and other masonry materials provide the greatest protection from fire, and insulated windows contribute even more to architectural resilience.
Christian Roberts-Olsen // Shutterstock
- Economic damages between 2010–20: 0.0233% of GDP
When constructing buildings and homes to avoid wildfires, choosing the right location is crucial. Ideally, construction wouldn’t take place in any danger zones, but that’s not always possible. It’s important to consider the climate, wind patterns, vegetation, and escape routes when choosing where to build.
Consider the structure itself—for example, patios are more resilient than decks. Typically, patios are made from non-flammable materials whereas decks are made from wood and can trap vegetation beneath them, which act as fuel. For similar reasons, slab-on-grade and full basement foundations provide more protection as opposed to pier foundations or crawl spaces, where vegetation and other flammable debris can accumulate. Building a house from concrete and other masonry materials provide the greatest protection from fire, and insulated windows contribute even more to architectural resilience.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
nvelichko // Shutterstock
- Economic damages between 2010–20: 0.024% of GDP
Buildings must be designed as a source of water to be resilient to drought. The type of water that can be produced or collected from a building include graywater, blackwater, rainwater, stormwater, or foundation drainage.
Graywater is the leftover water collected from showers, washing machines, and bathroom sinks, and it’s the cleanest kind of water that could be collected from a building. While it is not potable water, graywater can be used for irrigation, laundry, and for flushing toilets. This makes it so potable water does not have to be used for those purposes. In San Francisco, the capture and reuse of this non-potable water is mandated for new buildings.
nvelichko // Shutterstock
- Economic damages between 2010–20: 0.024% of GDP
Buildings must be designed as a source of water to be resilient to drought. The type of water that can be produced or collected from a building include graywater, blackwater, rainwater, stormwater, or foundation drainage.
Graywater is the leftover water collected from showers, washing machines, and bathroom sinks, and it’s the cleanest kind of water that could be collected from a building. While it is not potable water, graywater can be used for irrigation, laundry, and for flushing toilets. This makes it so potable water does not have to be used for those purposes. In San Francisco, the capture and reuse of this non-potable water is mandated for new buildings.
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A disastrous megaflood is coming to California, experts say, and it could be the most expensive natural disaster in history
FotoKina // Shutterstock
- Economic damages between 2010–20: 0.2313% of GDP
Residences continue to be built and bought close to oceans, in spite of the rising sea levels and increasing storms caused by climate change. To make these homes more resilient in the face of storms, there are a number of techniques that builders and designers can use.
For example, when homes are round they are more aerodynamic, deflecting airflow around the structure instead of absorbing the force. These round buildings get 30% less pressure building around them than a conventionally shaped home. The use of high-quality materials plays a big role as well—materials such as plywood and metal—and roofs should be anchored well so they don’t fly off. The elevation is important, too: Deltec Homes, a company that builds storm-resilient homes, recommends building at least 2 feet above flood surge.
While all these tips are important, when storms are bad enough and evacuation orders go into effect, the most important thing is still to listen to that guidance and evacuate.
FotoKina // Shutterstock
- Economic damages between 2010–20: 0.2313% of GDP
Residences continue to be built and bought close to oceans, in spite of the rising sea levels and increasing storms caused by climate change. To make these homes more resilient in the face of storms, there are a number of techniques that builders and designers can use.
For example, when homes are round they are more aerodynamic, deflecting airflow around the structure instead of absorbing the force. These round buildings get 30% less pressure building around them than a conventionally shaped home. The use of high-quality materials plays a big role as well—materials such as plywood and metal—and roofs should be anchored well so they don’t fly off. The elevation is important, too: Deltec Homes, a company that builds storm-resilient homes, recommends building at least 2 feet above flood surge.
While all these tips are important, when storms are bad enough and evacuation orders go into effect, the most important thing is still to listen to that guidance and evacuate.
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