female narrator: In November 1861, it started to rain in California and did not stop for 43 days.

The entire Central Valley was under water, along with much of Southern California and many parts of the West Coast.

Southern California's history and environment were forever changed by what experts call the California Super Flood.

It was the largest collective flooding event in California, Arizona, Nevada, Oregon, and Washington in over 300 years.

Authorities warn that even during times of drought, Southern California could face another big winter.

♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ female announcer: This program was made possible in part by a grant from Anne Ray Foundation, a Margaret A. Cargill philanthropy.

Will Cowan: When does the disaster start?

Does the disaster begin when the first raindrops fell?

Does the disaster start, you know, when the clouds are on the horizon?

Or does the disaster start when they decide to build, you know, the capital of the state of California in a seasonal lake bed?

♪♪♪ Dr. Lucy Jones: 1861-'62 is the worst natural disaster to hit California.

It killed 1% of our population and destroyed 1/3 of the taxable land and changed the economy of California.

We were a ranching economy.

Think about your visiting to the missions, right?

It was all ranching, but we wiped out the herds with the flood.

They drowned.

Half a million sheep, 200,000 head of cattle were drowned in that storm, and they had to abandon them and turn to farming because they couldn't afford to restock the herds.

So a really and a true catastrophe changes the economy, changes the society it leaves behind, and that happened in 1861-'62.

female narrator: Abraham Lincoln was president, the country was in the midst of a civil war, and Californians were a few years past the gold rush.

Meanwhile, local farmers were desperate for rain, but no one expected such a big winter.

Will: From November of 1861 to, say, March of 1862, from British Columbia to Baja California was a series of rain storms and blizzards that pretty much overwhelmed every waterway on the West Coast.

There was something like 84 inches of snowfall in a 24-hour period in the Sierra Nevada, which could you imagine, you know, something like 7 to 10 feet of snow overnight, more or less?

Southern California dodges the brunt of most of the big winter until about Christmas Eve about the end of December where the absorption capacity of the soil of Southern California just kind of reaches its max.

And you start getting overflows, and you're also getting effects from melt from the mountains.

And every river system in Southern California basically gets supercharged and overflows.

There's a description of it being a sheet of water, you know, from one set of mountain ranges to the other.

The entire Central Valley of California becomes a 500-mile contiguous lake system from Redding all the way to Bakersfield, more or less.

You could take a steamboat from San Francisco Bay all the way down to what's now Bakersfield and, in fact, they did, to rescue people and to deliver supplies and stuff as the winter wore on.

Coastal California, so the Bay, Salinas, Southern California also tremendously overwhelmed, massive floods in all those regions.

And, of course, in Southern California, kind of the A-frame of that, you know, of 1860s SoCal of San Diego, San Bernardino, and Los Angeles were all inundated, were all devastated by these rains and floods.

San Diego River floods across the entire plain.

I think only one house survives, and it only survives because the people there open up all the doors and windows on the ground floor and allows the water to flow through.

♪♪♪ ♪♪♪ Sharon Kasner: We're standing in front of the Trujillo Adobe in northern Riverside.

This adobe was built after the flood of 1862, which wiped out the initial village that was built when the settlers came in 1842.

This was the first overland route to Los Angeles that you didn't have to go by ocean.

Of the south side of the river was called La Placita de los Trujillos because the elected leader was Lorenzo Trujillo, who happens to be my three times great grandfather.

And he was one of the trail bosses that led the various expeditions coming to California.

Father Borgata, the priest, heard the roar of the water coming, and he ran outside and saw that there was a flash flood coming.

So he rang the bell, warned all the residents, and everyone was able to flee to safety.

No lives were lost.

So in 1866, there was a new parish priest and he said, "We need a new bell."

They melted it down and they cast a new bell in the sand of the Santa Ana River.

And the bell at the Mission Inn contains the bell that saved the community.

Will: So the case of the Agua Mansa reminds us of the vulnerability of certain populations in certain geographies.

Of course, they also tell us about resiliency, which is these folks, even before this flood, had faced so many obstacles.

And yet, it's after this flood that, perhaps, they showed their strongest case of resilience as it's, you know, the Trujillo sons who are out there the very next day, digging new irrigation trenches, planting new crops, getting ready to rebuild the town that they had built, you know, 20 years earlier.

female narrator: The community at Agua Mansa didn't understand why the rain kept coming.

But today, we know about the rivers in the sky.

Alex Tardy: So atmospheric rivers, in general, are wind transporting moisture across the Pacific for us in California.

So every storm that we get off the Pacific has atmospheric moisture, right, but not all of them can be classified as an atmospheric river.

So we look at the magnitude of the wind, say, comparing 10-mile-per-hour wind versus 50 mile per hour, that will transport the 50 mile per hour much more moisture than, say, 10 miles per hour.

So it's a lot like a highway system where you can get so many cars on a highway.

You're not gonna get as many when the moving slow, right?

You're not gonna get as many when they're congested.

But with an atmospheric river with fast-moving wind speeds, which we call jet streams, combine that with tropical moisture, which by definition is abundance of moisture so it's not something like average moisture, it's tropical, it's abundant, it's warm.

In other words, it's the ingredients to making a lot of rain.

Will: Atmospheric rivers are an ancient force, an ancient geologic force, an ancient hydrologic force, that has shaped and reshaped this landscape and therefore, the people on that landscape for thousands of years.

The indigenous peoples of North America described these forces in their stories in their oral histories.

These are powerful forces, powerful beings, that help transform the land and help transform the humans's relationship to the land, people's relationship to the land.

Dr. Sean C. Milanovich: In 1862, there was a lot of rain, and all that rain just came barreling down the canyon and our people had to disperse.

We didn't want to be in its way.

Some people had lost their lives.

And because of all that rain, some of the people went to Malki to Morongo Reservation and others went to Zeke into the Palm Springs area.

There's actually several examples, anecdotal examples, of native peoples predicting that the storms were coming, right.

So one in particular is with Sam Clemens in Nevada.

You know, he comes across this camp of Paiute peoples, and they're gathering their camp and they're moving up to higher ground.

They're warning everybody there's a storm coming.

And Clemens, of course, chuckles at these people thinking that they're foolish.

Clemens kind of looks up and shrugs his shoulders.

It's a blue sky, you know?

Moves on with his day, and it's that night that the storms come.

And Clemens almost doesn't survive that winter.

And because the big winter of 1862, there's almost no Mark Twain.

What's weird, though, is it's also because of '62 that there is a Mark Twain because that's his first big book is "Roughing It."

And what's fascinating about this particular event in "Roughing It" is it's kind of under told, right?

It's told as this kind of quirky story where he gets trapped on an island in the desert waiting for the floodwaters to reside.

There's something odd but the great teller of American tall tales undersells the biggest winter in the American West.

female narrator: And another big winter is possible.

In fact, the United States government considers another West Coast super flood to be such a threat that it ran a large scale simulation in 2010 to determine what kind of damage similar storms might do today.

Dr. Jones: At the US Geological Survey, I was asked to head a project called the Multi-Hazards Demonstration Project to demonstrate how hazard science can improve the community's resilience to natural disasters.

We started with a model of the San Andreas Earthquake.

That's what our--the people here wanted from us.

They wanted from the science.

"I'm getting ready for an earthquake, what am I getting ready for?"

And then we went to turn to flooding.

We actually partnered with the Art Center College of Design and tried to think about, how can we talk about this?

How do we recognize that, in fact, these storms are deadly, that they have a lot of consequences?

And who's afraid of the rain, right?

It's hard to get people to plan for this.

They came back and said, "We want to call it Kill Storm."

And we went, mm, yeah, that's not really the way we want to talk about it.

Yes, we want people to take it seriously, but we don't want to be terrifying them.

And one of our scientists said, "Well, why not just make it Atmospheric River 1000, and then it becomes an ark?"

And it gave the right idea.

Will: So the ARK Storm, it stands for AR as in Atmospheric River, and the K stands for 1,000 because they consider 1,000-year storm.

And, of course, that doesn't necessarily mean that this is a storm that will happen every 1,000 years, but that there's a 1 in 1,000 chance of this storm happening any given year.

So when you think about it that way, it's like, oh, it could actually be this year or it could actually be next year.

Dr. Jones: It isn't, in fact, a statement that this is a 1 in 1,000 year event, right?

In fact, when we look back in the history of California, we can see like in deposits off of rivers, where there have been sediment dropped in big storms that happen every few hundred years, and we don't see 1861-'62 in that record.

So it does imply that those storms are bigger than the one we had in 1861-'62.

So the type of storm that can really devastate California looks to happen every couple hundred years or so.

Will: For the Qui people in our oral stories, it's been passed down that the sea has come and gone multiple, multiple times.

And sometimes the water has come just gushing in real quick.

Other times, the water has come in slowly.

And so, for our oral stories, we've been told it's been--occurred four times.

Dr. Jones: In fact, the Ark Storm, as we modeled it, is smaller than the flood of 1861-'62, but it still is capable of flooding 24% of the properties in California, ends up costing about four times as much as the San Andreas Shakeout Earthquake would and the reason being is that it's a statewide event.

So it goes on to many more people.

Instead of ten million near the San Andreas, we now have the 40 million over the whole state.

Katrina was a shock to the United States with 1800 dead.

How could we be killing people from flooding?

Why couldn't we get them out?

And, of course, there's a lot of reasons behind that, but we didn't plan for the real storm.

We modeled what the worst would be and planned for what the best would be, and we weren't ready to handle it.

Will: So it's often these parts of a town that suffer the brunt of these environmental catastrophes because they're often at lower levels, lower elevations.

You know, and so it's the poorest people of color who suffer the brunt of these storms.

Think Katrina.

♪♪♪ Will: But perhaps one of the most egregious examples of environmental justice and social justice and racial justice tied to 1862 is the case of Chinese Californians, particularly Chinese Californians in the Central Valley.

When these storms come, these Chinese miners had built these kind of not just mining camps, but there was full-fledged towns.

In fact, there this one on the Yuba River that I've kind of playfully called the Chinese temple town because there's, in fact, a temple they built there that they had dug down into this island on the river with a drawbridge and a wall and a moat.

You know, like, it sounds like something out of some medieval fiction, but this is something the Chinese in Yuba did to defend themselves, likely, from white miners and other violence that was occurring against them.

So it actually ends up being their detriment because when this flood comes, all these Chinese miners, they run into their palisade, kind of, and the water eventually goes up over the walls and into the town and drowns the town out.

And there was accounts of it hundreds, perhaps even a thousand, perhaps several thousand of Chinese Californians who are lost, who are killed, who died in these floods.

And perhaps the biggest tragedy is during a winter that had so many examples of true bravery of selfless heroism, it seems that very few, if anybody, stepped in to help any of these Chinese miners in the moment or in the aftermath.

Will: There's a lot of different types of stories.

And so, there's these stories of pure heroism where, you know, where a single guy goes out and collects, you know, dozens, if not a hundred people himself on his little boat or on his steamer.

One of my favorites, this is told from Central Valley, California, where a recent immigrant, he's running away as the water's kind of coming in towards his new farm.

And he climbs up a tree, and he gets up there in like the crotch of a branch.

And he's sitting there and catching his breath.

And he looks down, and it's carved into the branch it says, "1850," implying that someone else had to find refuge there when the big flood of 1850 hit Sacramento, right?

So again, the reminder that these floods are not necessarily, you know, new or exceptional but for that person, there was this kind of funny irony in, like, here he is again, you know?

Probably some of the stories I really enjoy the most are the kind of jovial, almost party-like atmosphere, particularly around Sacramento.

There's all of this suffering going on, and there's something probably about gallows humor here and when times are hard, people will find ways to party harder maybe.

There's brass bands in boats floating down, you know, downtown Sacramento, which is basically now, you know, California's Venice where people are, you know, singing and drinking and partying and living it up.

While at the same time, there's people on the outskirts who are freezing and shivering and starving with no dry wood for fuel, for fires, and no, you know, dry bedding or dry clothing.

female narrator: Fortunately, modern-day scientists and researchers have the ability to warn communities about future mega storms.

Alex: With today's technology, including satellites, weather forecasts, modeling, we have notification systems that can let someone know seven to ten days in advance that not just a little bit, but a lot of rain is coming into your area and that you are at a high risk and now is the time to start taking action.

Dr. Jones: ARK Storm has given us the chance to do a better job of planning, to talk about it, to recognize that floods are a real danger.

And with the right coordination, we're gonna handle it and we're gonna have big economic losses, but I don't think we'll be having a death toll.

One example is the community around Lake Tahoe.

One of the things we saw was that a big enough storm could disrupt all of the roads leading into Lake Tahoe.

Because of all that, they were able to change the way in which they planned the response, making sure they have local abilities.

And when those huge storms came a few years ago, we actually did see all of the roads into Lake Tahoe blocked off, but they were able to deal with it.

They didn't have the problems that might very well have happened if we didn't do that planning.

So what we see is people can use this information to both prevent losses, but also plan for the response in a way that really reduces the impact on all of us.

female narrator: With the help of satellites, meteorologists would be able to give Southern Californians advance notice of a potential super flood scenario.

But there are factors on the ground that also determine how destructive these storms will be.

Alex: So atmospheric rivers in California are critical vital to our water supply.

So it rains, it comes down as runoff, it fills up our reservoirs.

Sometimes it comes down as snow, and that's even better because we can manage that into our water supply.

But the bottom line is up to 60% of that rain and that runoff and that water supply comes from atmospheric rivers annually.

And each year, about three to five of those hit Southern California, as much as 15 to 20 of them on an average year will hit Northern California.

So the average storm for Southern California will bring 1 to 2 inches of rain.

An atmospheric river, especially a strong one, will bring upwards of 20 to 30 inches of rain to our mountains and all that water will flush down into the valleys and coasts.

So standing here in the Santa Ana Mountains of Southern California and Silverado Canyon, we're a perfect example of a catastrophic rainstorm and what that can do.

And the reason being is these beautiful mountains behind us act as a catch, like a catcher's mitt.

They catch all that atmospheric river transport, all that heavy rain, and they bring it all down into a narrow corridor and cause devastating flooding.

Will: So North American West is a bricolage of all things past, a combination of plate tectonics and hydrologies that have created this very young and dynamic landscape, and that's really key to understanding how water works.

So west of the Continental Divide, west of the Rocky Mountains, is actually geologically and hydrologically different than east of the Rocky Mountains.

The slope is greater, it's more dramatic, so therefore, water moves faster on this landscape and, of course, it forces other things on the landscape to also move faster.

Dr. Jones: When a flood happens, the water can move up and the water can move down.

When the water moves up into your house, it's called a flood.

When the water moves down, flows down into your house, it's called a debris flow.

When the debris flow happens, the water's flowing over the hill, and it picks things up along the way.

And the faster it's moving, the bigger the material it can pick up.

And we have plenty of reports and evidence of huge boulders, boulders larger than houses, coming down the mountain having been carried in these debris flows.

Historically, they are some of the most dangerous phenomena in California.

We have killed more Southern Californians in floods and debris flows than we have in earthquakes.

And, of course, the financial and economic damage that they can do is extreme as well.

Alex: But there's two types of mud and debris flows that occur.

One of them is a landslide.

Too much rain on a mountain slope, it gives way, trees, rocks, everything can come down.

It can result in catastrophic damage and even fatalities, not predictable.

On the other hand, there's a debris and mud flow that's specifically related to a post wildfire burn scar.

The main difference is we can predict those post wildfire debris flows.

female narrator: Wildfires make California's terrain especially vulnerable to the effects of heavy rain.

Alex: In an area where you had a recent wildfire or burn scar across this terrain, that's what makes it more susceptible today because up to five times as much water will come rushing down in the same type of storm into these canyons, into the rivers, into the creeks.

Now, we had fires, you know, back in 1862, but the frequency is increasing now and now we have more people living in these areas.

And we didn't really understand, even back in 1980, what a burn scar could add to the same type of rainstorm.

So here's some clear evidence of recent force, high force of water flow coming down the canyon.

These sandbags were put in place upstream to protect the road and protect people's property, and here they are down in the middle of the creek, along with, you know, burned wood and all this rock likely deposited this past year.

And then finally, because of all that water, fresh weeds growing on top of it.

Will: The winter of '61-'62 was a big impetus in the desire to transform the landscape.

We've rebuilt our water infrastructure to flush out the storm water as quickly as possible so that there's not the danger of floods because, again, Southern California is a flood basin.

Like, this entire geography, with the exception of the few little hills that pop out like islands, is historically a place that flooded.

However, the flood-control infrastructure is not really designed for a flood of this magnitude.

What I want my students to take away is to really pay attention to where you live.

Are you in a floodplain?

Are you in a 100-year floodplain?

Are you in a 200-year floodplain?

Are you in a 500-year floodplain?

And most of us don't know that, and I think that we should.

Dr. Jones: So because insurance wasn't actually designed, it just evolved by what people were willing to cover or not, we end up with a situation where most of the natural hazards are covered, not included in general insurance, and you have to specify that you're adding them.

So earthquake or flood or wind, and all of these are done separately.

And it becomes a place for the insurance companies to argue they don't cover that one.

I think if we were doing this rationally and we actually wanted our society to be able to recover after a disaster, we would sell natural hazard insurance that actually reflected the costs.

We would be encouraging development in the appropriate places, and we would not be facing the situation where we would lead into depression after a big disaster because we didn't have the funds and the resources to recover.

Alex: In your neighborhood, in a community like this, you have to be aware of your surrounding of your threat.

Is there a recent burn scar?

Is there or not?

Where is the history of flooding?

Just building a wall by your house is not gonna solve the problem.

What will happen in those situations is the water will go into your neighbor, or you'll block the water and the flood will be twice as bad.

And be aware of your entire surrounding, your entire neighborhood, about where can we basically send the water to?

An atmospheric river, a heavy rain event, is predictable.

You can have a plan to either put out the sandbags, a plan to evacuate, a plan to notify your neighbors, or a plan to be notified by the authorities locally that "Okay, it's too much, you need to get out" type of thing.

And you could also have a long-term plan where you work in your neighborhood to allow that water or that runoff or that debris flow to more naturally go where it needs to go instead of your backyard or your immediate neighborhood.

female narrator: Like the first peoples and early settlers, modern Californians must understand the potential dangers of living in this area.

Further coordination between the state and local officials, developers, and insurance companies can help to keep property and residents prepared.

Dr. Milanovich: For a lot of people, we had multiple homes.

There was usually a summer home so when it was hot, you would go into the mountains where it was cooler to the heat to the wind when there was too much water, when there was not enough water.

We were adapted to the natural environment.

Sharon: As I was growing up, my grandfather, from the time I was probably ten years old, it was drilled into me that you never live west of Orange Street.

It flooded once, it can flood again.

So in 2012, there was a metal sculpture dedicated to Lorenzo Trujillo at the Agua Mansa Cemetery, but most of us have miniature necklaces made of that sculpture that keeps us in touch with our family.

These were tremendously resilient people.

We are still here.

Our families came 180 years ago from New Mexico.

And today, 180 years later, we are still fighting for this land and for this building.

♪♪♪ ♪♪♪ ♪♪♪ female announcer: This program was made possible in part by a grant from Anne Ray Foundation, a Margaret A. Cargill philanthropy.

...