Megaflood: California’s disaster in waiting | Go in-depth with our 4-part series
New research indicates 'megafloods' are twice as likely in the future due to our changing climate.
When you think of California's climate, drought probably comes to mind first, but California has a long history of floods. Some floods were so punishing and relentless they crippled the state.
New research indicates these "megafloods" are twice as likely in the future with a changing climate. It's a future we can't avoid, but we can learn from the past and prepare.
ABC10's team of meteorologists investigated the topic, answering questions like: What exactly is a megaflood? Can our infrastructure withstand it? What would an emergency response during a flood look like? How can you prepare your property for a flood?
Part 1: What is a 'megaflood'?
Imagine the biggest storm you have been through — cold, hard rain for a few days. Ponding on roads and creeks. Rivers running high.
Well, what if the rain didn't stop, the creeks rose higher, and the rivers became an inland salt-less sea spanning hundreds of miles? The water once seen as our friend would become our biggest enemy.
"When it started raining in November, people started to notice that winter's coming early," said Old Sac Underground tour guide, Shawn Turner. "Then right before Christmas, the storms really hit."
For folks living in California in 1861 and 1862, this wasn't a bad dream, it was a nightmare. Their livelihoods were washed away.
"There proceeded to be continual rain for 43 to 45 days. The storm was started with a heavy cold snow, followed immediately by a very warm rain that washed down all that snow," said Turner.
Turner takes visitors in Old Sacramento back to this time and place of the great flood. To do this, you must go down to the underground where the city was originally built.
"Because of that heavy amount of water and debris coming down out of the hillsides, that levee was no match for the American River, breached the levee approximately where businesses are now," said Turner. "The water then came in and flowed behind the city."
Sacramento was inundated and annihilated by the biggest flood ever recorded by the new settlers.
"As the story goes, life must go on and in the middle of the great flood, we had to swear in a new governor," said Turner. "His name was Leland Standford and he lived right here in downtown Sacramento. He had to take a rowboat to the capitol to be sworn in. The water would remain here for the next three months. The great flood created an unbroken body of water for 250-300 miles. It also flooded Southern California as well. This one-two punch bankrupted the state, and propelled Sacramento to look forward, and lift everything up.
We're standing next to the foundations for the Hastings building, Benjamin Franklin Hastings and company building, this building has been lifted up. Up to the current level, this was a 500-ton brick building. That was one of the hundreds of buildings that were lifted over a 13-year span to lift the central business district up out of the floodwaters."
Since the great flood of California and the lifting of Sacramento, we haven't seen the water that high... but we know there will be another time.
As chaotic as California weather can be, it's also consistent. History tells us well before we could document it that these floods happen every 100 years or so, and more are coming.
The confidence of catastrophe casting lies in our understanding of the main ingredient of these floods: atmospheric rivers — or ARs.
"An atmospheric river is literally a river in the sky," said Marty Ralph, an expert on atmospheric rivers. "It's just a river of water vapor moved by the wind rather than a terrestrial river in which liquid is moved by gravity."
Ralph says calling these ribbons of moisture a river isn't an exaggeration. In fact, it might be understating California's primary source of water.
"So, an average atmospheric river transports the equivalent to like 25 Mississippi Rivers worth of water. Its vapors, when that hits shore or hits the mountains, it's forced upward and some of that can condense into clouds and rain and snow in vast quantities," said Ralph.
40-60% of California's water comes from ARs. If you get less than you expect, you are in a drought. If you get more, you flood. Much of the research lately is focused on forecasting atmospheric rivers, especially the super high-end ones capable of breaking the flood banks.
The great flood was the blueprint for a megaflood scenario called the "Arkstorm Project" back in 2011, a collaboration of more than 100 scientists and officials. At the time, it was the best understanding of the worst-case scenario.
The report was sobering, to say the least. A cycle of major atmospheric rivers would "overwhelm the state's flood protection system," prompt evacuations for more than a million people, and cause nearly $1 trillion in damage — 3x the damage as a massive California earthquake we've also feared.
In short, a flood of this magnitude is California's biggest threat. Just like that earthquake, we know it's coming, except the future megafloods will likely be worse.
"The most extreme precipitation events, which in California almost always means the most intense atmospheric river storms, are likely to become significantly more intense," said Dr. Daniel Swain, a climate scientist at UCLA.
Swain, co-author of Arkstorm 2.0, is researching what a megaflood could look like in our warming climate. He found these storms are now twice as likely to happen in any given year.
Right now, and in the future, we can expect 2-4x more runoff and flooding potential than we have historically observed.
"This ends up being a really critical aspect in the Sierra Nevada in particular, because not only are you seeing atmospheric rivers that bring more water, but more of that water is falling as liquid rain rather than frozen snow," said Swain.
The report has brought our history with megafloods back to the future and understands California's other big one is coming, and we need to be ready.
We realize this report and expert analysis is concerning, to say the least, but other experts and policymakers are aware of this new megadrought probability and are reimagining and rebuilding California's flood protection system.
Part 2: Can our infrastructure withstand a 'megaflood'?
From drought to flood, it’s the vicious cycle of weather extremes in California.
It may be hard to imagine more than seven million Californians are at risk of flooding as we enter our fourth year of drought. In fact, in the past 20 years, every California county has received a flood-related emergency.
In the second part of our "megaflood" series, we’re looking at why our system of river levees, dams, and reservoirs put the Sacramento and San Joaquin Valleys at one of the top spots in the country for flood risk.
"We're already in a world where the likelihood of a catastrophic flood has doubled in any given year," said Brian Johnson with the Central Valley Flood Protection Board. "That's the kind of thing that keeps people like us up at night."
The mission of the Central Valley Flood Protection Board is to update the state’s plan to keep us all safe from catastrophic flooding.
"People talk about how we may be overdue for the 'big one' for an earthquake in Northern California," said Johnson. "That's probably true for the big flood as well."
It would be a flood event dwarfing the record-breaking water year of 2017, when the Oroville Reservoir couldn’t hold the amount of water coming in from the rain and Sierra snowmelt.
"In February of that year, we had a series of storms coming into the lake. We were operating the lake like we normally do to hold back some of the water and then release it gradually into the Feather River when we found the damage in the spillway," said Ted Craddock with the California Department of Water Resources.
The damage made it nearly impossible to release enough water from the rapidly rising lake, putting pressure on the country’s tallest dam -- standing over 70 stories high -- and its spillways.
The risk of massive flooding grew by the hour for people living in the valley below.
"As a mom, the first thing I thought [of] was my family," said Mariana Rodriguez, who evacuated in 2017. "You know, it was very scary at that moment."
With one set of parents down the street and the other 20 minutes away, Mariana and David had to move quickly.
"It was mayhem for a while. People were going crazy here in Oroville," said David Rodriguez.
A life they worked so hard to build was hanging in the balance.
"Friends here, our house where I was born at," said David. "We built this ourselves here. We put the trailer here, we put the porch here, things we worked on [put our], blood, sweat and tears into it. I mean, imagine all that going down."
"You work so much," said Mariana. "You just felt like somebody just took it away from you."
The Rodriguez's remember the night they and nearly 200,000 others got the call for immediate evacuation.
The state responded to reduce the risk of a repeat.
"13 million pounds of reinforcing steel was put in place here," said Rodriguez. "Then additionally at the emergency spillway over to the left here. We placed 750,000 cubic yards of concrete to help protect the hillside."
ABC10's Monica Woods visited the country’s tallest dam, holding back over 3.5-million-acre-feet of water. If the whole facility were to fail, it would send all the water rushing downstream; flooding places like Oroville, Marysville, and even into Sacramento. Some places would end up under 100 feet of water.
The valley is a natural floodplain sitting thousands of feet lower than our highest peaks, snowmelt and runoff move downhill filling reservoirs. When water is released, it keeps moving downstream to rivers, a dangerous place for accumulating water.
"The Sacramento River as a whole is called a perched river, which means the bottom, the flow line, the bottom of the river, in many cases is higher than the land that's on each side of it," said Todd Bernardy with the California Department of Water Resources. "The river is actually higher than the surrounding land."
The only thing holding back the water is the levees.
"In the Sacramento region alone, there's over 514,000 people that are protected by these levees," said Bernardy.
One break in the system can cause deadly and massive destruction like the levee breaks in Yuba County in 1986 and 1997.
"The communities that would most likely be affected would be in the low-lying areas of the valley," said Bernardy. "They were effectively wetlands and now they're being protected by levees."
Natomas, West Sacramento, the city of Sacramento, Stockton, Lathrop, and Manteca are home to large growing community developments, and that’s why close to $8.3 billion is being spent on levee improvements through a federal civil works program.
"By the funds that have been allocated, we've improved about 140 miles of the 300 miles with about another 160 miles more to go," said Bernardy.
It will offer protection to about 1.1 million people and over $100 billion worth of assets.
Near where the Sacramento and American Rivers meet, another big project is underway to move water away from high-risk areas in Sacramento and Yolo counties.
"This is the lower Elkhorn Basin Setback project," said David Pesavento with the California Department of Water Resources. "We’re setting back the existing Sacramento Bypass levee by approximately 1,500 feet and the Yolo Bypass levee by approximately 1,500 feet."
This will help alleviate downstream water flows by allowing more water to flow into beneficial areas for agriculture and the environment.
"This project is being implemented in close coordination with another project coming shortly, the Sacramento Weir widening project," said Pesavento.
Together they will reduce the water surface elevation in the Sacramento River by as much as a foot, adding another layer of protection during big flood events.
But these structural changes can only do so much in the face of climate change with research showing California’s risk of a MegaStorm doubling due to warming.
"It will be a challenge, for sure," said Joe Forbis with the U.S. Army Corps of Engineers. "Because the infrastructure that was constructed back in the 30s, 40s, and 50s, like the dams and levees, and the hydrology information that was available at the time at which those structures were designed is pre-all of this."
Forbis says this is a time of renaissance with improving forecasts giving water managers like the U.S. Army Corps of Engineers new flexibility in a program called FIRO.
"It's FIRO, or Forecast Informed Reservoir Operations," said Forbis. "It's this idea that if you understand forecasted events better, if you can get better forecasts, then you can make better water management decisions."
Like knowing when to keep water in, and when to let water out.
"We’ve made significant progress, but that progress isn’t happening on a pace and scale we know is needed and with climate change, winning slowly is losing," said Johnson.
Todd Bernardy from DWR put it plainly -- it’s like getting into a car without a seatbelt. You hope you don’t get into an accident, but if you do, the seatbelt can save your life.
If the flooding weather events come, we’ll be glad these protections are in place. And it’s not just building new infrastructure, the state is looking at ways to restore what was naturally here.
A great example of this is the Dos Rios Ranch project near Modesto. Through a collaboration with a group called River Partners, this would be the first state park in 13 years and the largest floodplain restoration project in state history, reducing the risk of flooding and providing more equitable access to water.
Part 3: Emergency response during a flood
Atmospheric rivers, which are intensified by climate change, account for more than 90% of flood damages in California. These storms present the biggest threat to our low-lying areas sitting below levees.
Liz Bryson is the Manager of Flood Operations at the California Department of Water Resources. Bryson and the DWR lead the state’s flood response. When activated, people pack a relatively small and unassuming room in Sacramento.
"One big part of what we do during high water is facilitated discussions between reservoir operators because those releases into the rivers could have major impacts downstream," said Bryson. "So, we want to make sure that all the appropriate agencies are in the conversation so they're not just making decisions in silos. Emergencies begin and end at the local level, so when a local agency runs out of resources, they move up to the county, and the county runs out of resources, they come up to the state level. The flood operation center coordinates and supports that response.”
The Flood Ops Center was activated in 2019 for four days. In comparison, the center was active for 151 days in 2017 -- the year of the Oroville Dam Crisis.
Nearly 200,000 people living downstream from the dam were told to leave their homes. It was a crisis Butte County Sheriff Kory Honea remembers well.
"There's been an ongoing effort to try to get people to understand that we don't issue these warnings lightly," said Honea. "They're based on the best information we have at the time. They're based on our experience with these kinds of events and asked that they heed those warnings and move to an area where they're much safer. One of the things that we found or learned is that the most effective way to get somebody to evacuate is for a uniform law enforcement officer to go to their house, knock on their door, tell them of the emergency and tell them what they need to do. Sometimes you don't have the time for that and certainly (the) spillway incident was one of those instances where we did not have time."
In 2017, Sheriff Honea personally called David and Mariana Rodriguez to tell them to leave their home.
“I said, 'Alright, well, we're going to try to get out of here fast as I can and I know a bunch of backroads,'" said David Rodriguez. “It was able to get me pretty fast to the Knights Landing area. Everybody was trying to go out to either Woodland, Colusa, different areas. Once I hit Knights Landing to Woodland, it took me about two hours to get into Woodland, which should be only about a 20-minute drive.”
They opted to take the backroads instead of the major thoroughfares, something not recommended if there's flooding.
“There absolutely are designated flood emergency routes from every community in Sacramento County in San Joaquin County and up and down the valley,” said John Cain with River Partners.
Cain works to restore natural floodplains and bolster defenses protecting flat, low-lying cities in the Sacramento and Central valleys.
“What building in the floodplains does -- behind a levee or below a dam -- is puts a whole bunch of people in harm's way and enriches some developers that put houses in the floodplain," said Cain. "They're not paying for the dam. They're delivering a check, almost certainly not a check... a bill, almost certainly to future generations to have to pay for that foolish development.”
Following the Hurricane Katrina disaster in Louisiana, officials put a building moratorium on Sacramento’s Natomas neighborhood until 2015 over concerns the levees were not strong enough.
Currently, the levee system in place is still being upgraded to better withstand heavy storms.
"What's really important is everybody understands what the evacuation route is," said Cain. "It's particularly important for residents to know where to go and where not to go. Sometimes people think all I got to do is get out of town. Well, you could be driving right into the flood."
Renderings from Sacramento County show the evacuation route should a levee fail in South Natomas. Large portions of the area would be underwater in hours.
If a levee broke in the area around Old Sacramento, most of downtown and the Pocket would be under 16 feet of water within a day.
As we live and continue to build in flat, low-lying cities in the valley, it’s important to know your way out should disaster hit. Your best defense against flooding is to be prepared.
- City of Sacramento flood evacuation map
- Sacramento County flood evacuation maps
- San Joaquin County flood evacuation maps
- Butte County flood evacuation maps
- Placer County flood information site
- City of Roseville flood simulation map
- Solano County flood information
- Stanislaus County flood information site
- Sutter County flood evacuation maps
- Yolo County flood evacuation maps
- Yuba County flood information site
Part 4: Preparing your property for a flood
What ends a drought instantly? Meteorologists will say enough water to recharge the soil moisture, water wells, and lakes... but what happens when storm after storm inundates a drought-stricken area?
The megaflood has been discussed — a series of atmospheric rivers being pulled in by storm after storm, bringing relentless rainfall with little recovery for cities between storms.
"There's a new model out and it's predicting that the mega storm is probably much more (a) reality than we know," said Frank Mansell with FEMA public affairs. "One of the things that we say at FEMA is that all droughts are followed by floods."
He says catastrophic events like floods are rehearsed all the time, and still with warnings to residents, many find themselves left wondering what to do.
"I don't know how many disasters I've been at where people had no idea what insurance policies they had. Bank account numbers, all that stuff that you take for granted as having, you will likely have destroyed in a disaster," said Mansell.
So, this begs the question: Are we really prepared?
Mansell works closely with flood insurance specialists with the National Flood Insurance Program. He says many people think they’re covered with home insurance and find out the hard way.
“Flooding can happen anywhere it rains because you can get street flooding," he said. "Levees are constantly under pressure, there's always water flowing past them, eroding at the base of the levee, and levees do overtop. It's a nice system, but it's not foolproof, and it doesn't offer 100% protection."
According to FEMA, over 90% of flood insurance policies are covered by the NFIP. Those interested can buy flood insurance through their current insurance company and participate in a “write your own” policy. The NFIP allows the insurance company to write and service government flood insurance using its own brand name.
Premiums are assessed through flood maps.
"After a community gets its flood maps, it also comes with a set of building standards for that community," said Mansell. "We assume that you as a homeowner building after the flood maps… after the flood maps are out, you are going to build to that new standard. You pay what are called actuarial rates. Those are rates that really reflect the risk."
The National Flood Insurance Program has paid $72 billion in claims to about two million policyholders, according to a statement by David Maurstad, a senior executive of the National Flood Insurance Program.
"The largest caveat is that FEMA will not duplicate benefits," said Mansell. "So, if my home is damaged significantly from a flood, for instance, if I've got flood insurance, FEMA won't pay you, we will pay you for everything your flood insurance doesn't cover up to a total of above $35-40,000."
Private flood insurance is beginning to gain ground in sales as more tools and forecasts for flood zones become available. Often private insurance can cost a bit more but can cover homes that are at a high value.
"The private insurance companies never got into the game really, until later," said Mansell. "Predominantly, they're usually higher, but not necessarily. So, you can shop around and compare prices, and you can also use private insurance to augment your national flood insurance program. So, if you thought your structure was worth more than $250,000, you may want to look at a private insurer to cover the balance."
The biggest misconception about flood insurance in California is that you don’t need it.
"Sacramento is at the confluence of two rivers," said Carlos Eliason with the city of Sacramento. "Some studies suggest that Sacramento is actually one of the top 10 in the nation, most at-risk for flooding due to rivers."
Flood maps around the Sacramento metro area show the regions near rivers, lakes, dams, levees, and canals are at risk.
Take Natomas, the Pocket, and south Eugene, each surrounded by major water sources. Still, it doesn’t mean outlying areas are safe.
"40% of our flood claims that we pay are for structures that are not in a flood zone," said Mansell.
John Cain with River Partners continues to advocate for public education when it comes to our water channels.
"Make sure you get flood insurance, even if you're protected by a levee because that levee could fail. Having a community of not just a few homeowners, but the whole community of people having flood insurance really helps the community build back from floods," said Cain.
While it’s important to protect your property, it’s even more important to protect your family. In an event of a megaflood, as seen in hurricane situations, it may take days to see flooding occur, and not just during the storm itself.
"Lot of folks need to just kind of take stock of their family situation, their housing situation, make sure that they know the evacuation routes that might work best for them, understanding that the evacuation routes that they think might be available may not be so making sure there's primary backup type routes available. What they drive to work every day during a major disaster might not be a route that's open," said Daniel Bowers, the EMA director for the city of Sacramento.
Those emergency to-go bags constantly mentioned in earthquake scenarios can also be used in floods.
"Having a kit that's fully inclusive of everything that they may need, including personal medications, pet supplies, things like that, that can accommodate everybody within their family," said Bowers.
In the event levees or drainage canals are inundated with water in a megaflood, you and your family will need to evacuate at a moment's notice.
Here are some additional items you’ll need in those emergency kits:
- Three days' worth of nonperishable food
- Can opener
- Flashlight and batteries
- Phone chargers
- First aid kits
- A whistle
- Important documents
- Clothing and blankets
- Cash on hand in case of power outages