Science Friday - Black Holes, California Megaflood. Feb 22, 2019, Part 2

Episode Date: February 22, 2019

When it floods in California, the culprit is usually what’s known as an atmospheric river—a narrow ribbon of ultra-moist air moving in from over the Pacific Ocean. Atmospheric rivers are also essential sources of moisture for western reservoirs and mountain snowpack, but in 1861, a series of particularly intense and prolonged ones led to the worst disaster in state history: a flood that swamped the state. The megaflood turned the Central Valley into an inland sea and washed away an estimated one in eight homes. What would happen if the same weather pattern hit the state again? Los Angeles Times reporter Louis Sahagun and University of California, Los Angeles climate scientist Daniel Swain join Ira to discuss the storms, its potential impact on local infrastructure, and why disastrous flooding events like the one in 1861 are not only becoming more likely as the planet warms, but may have already been a more frequent occurrence than previously thought. Plus: As a grad student in astrophysics at Cambridge University, Priya Natarajan devised a theory that might explain a mysterious relationship between black holes and nearby stars, proposing that as black holes gobble up nearby material, they “burp,” and the resulting winds affect the formation of nearby stars. Now, 20 years later, the experimental evidence has finally come in: Her theory seems correct. This hour, Ira talks with Priya about her theory. And Nergis Mavalvala of MIT joins to talk about why “squeezing light” may be the key to detecting more distant black hole collisions with the gravitational wave detector LIGO. Learn more here. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Ira Flato, coming to you today from KQED in San Francisco. Later in the hour, California's other big one could be a flood of biblical proportions. But first, when Einstein published his general theory of relativity in 1915, he still didn't have any evidence. It was actually true. Yes, the math worked out, and he had a few examples he could point to that seemed to confirm and conformed his way of thinking, for example, the hard-to-explain orbit of Mercury. But it wasn't until the total solar eclipse of May 1919 that Sir Arthur Eddington and his two teams of scientists were able to confirm that during the eclipse, a few stars whose light shot past the sun seemed a little displaced from their usual position, a sign that

the mass of the sun had caused a warp in space-time, sending the starlight on a very slight detour. Einstein was on the front page of newspapers worldwide the next morning. And that's how science works, right? You know, you got an idea, like Richard Feynman says, you get an idea, you prove it, you find the evidence, or at least wait until someone else can find the evidence. My next guest devised a theory that might explain a mysterious relationship between black holes and nearby stars back in grad school, and it wasn't until 20 years later that the experimental evidence came in, the theory seems correct. Priya Natarajan is a professor in the Department of Astronomy and Physics at Yale and New Haven.

Congratulations, Priya, and welcome back. Thank you very much. Happy to be back on Science Friday. So take us back. What had you and other astronomers noticed about black holes that spurred you to develop this theory in the first place? You mean going back 20 years ago? Way back when we're all babies. That's right.

So in 1999, we didn't know a whole lot about black holes. We knew that black holes sat in the center of pretty much every galaxy, and we knew that there were some black holes that were feeding copiously, and we see them as quasars. But in 1998, there was a curious correlation that was published for the first time. So a relationship between the mass of a black hole that is harbored in the heart of a galaxy and the mass of stars right around it. So this was very peculiar because, you know, black holes have a lot of a galaxy.

Because, you know, black holes have intense gravity, but the range of influence for them is really tiny, right? So, for example, if you take the black hole in the center of the Milky Way, which is four million times the mass of the sun, it's like having a penny at the center of the entire Earth compared to sort of that's the scaling in terms of our galaxy and the size of the hole. And so this was peculiar. How does the black hole that have such outsized influence on the stars, which are sort of like the inner core? of the Earth's core, how would the black hole actually influence that distance? It was a mystery. And so in my thesis, I was trying to actually work on the larger question of the connection between black holes and galaxies, whether they grow together and not much was known.

So then I had this bizarre idea, a speculative idea, was a bit of an imaginative leap, that perhaps just as black holes gobble matter, maybe they could push some matter out. they could drive a wind or an outflow. So maybe there's gas that they could actually push out, right? And that's because a lot of energy is released when a black hole is fed. And some of this energy could, you know, the luminosity could give pressure, radiation pressure and drive a wind that would sweep up material that's outside. So I sort of calculated that because, you know,

that allows you then to connect the large scale to the small scale. And then I did this calculation, and we wrote up a paper, and I did this with a postdoc at the time at the Institute of Astronomy in Cambridge where I was doing my PhD, Stein Sigurdson. And realized that there was a very peculiar signature that such a gassy, windy outflow around a black hole would have. And that would be that it would cost a very ghostly shadow on the cosmic microwave background radiation. So this is the relic radiation from the Big Bang that pervades us everywhere in the universe. And those photons, that light would actually be quite cold in the nearby universe. So when we receive it now, it's about 3 degree Kelvin. And this hot outflows from quasars would actually cast a shadow.

And this is called the Sunniayev-Zeldovich effect. And this is known. This was already predicted in the 1970s. But it was believed that you need a huge amount of hot electrons that are at a much higher temperature than this relic radiation to produce a shadow. And the only objects in the universe at the time we thought could do it were clusters of galaxies because they have a hot ball of gas in their centers. And nobody had thought that quasars could actually produce these big gassy bubbles that could

caused a similar shadow. And it turns out that there's not enough gas and quasars, but the Suniaev-Zaldovich effect has another piece. So there's a piece that comes from the gas being hot, and then there's a piece that comes from the gas moving fast. So if you add those two bits for these quasar outflows, then you get a pretty out-sized umphi effect that was potentially detectable, but in 1999 there was no apparatus. There was no radio telescope.

So this would be in radio frequencies, like 130 gigahertz. And there was no instrument operating at that time. So, you know, we did this calculation, and it was kind of cool and interesting. But we knew that radio telescopes were going to come online in the next decade or so, 10, 15 years. You know, I just moved on, and I wrote another paper on the implications of this gas, the fate of this gas, you know, what this burped gas is going to do. It might make globular clusters. It might make little dwarf galaxies with peculiar properties and so on. And then I moved on to working on other aspects of black hole physics.

And then lo and behold, 20 years later, late last year in December, I noticed that there was a first detection of this effect. And so it was pretty cool. Was the detection? Could it be isolated to a spot in the universe where it was all coming from? Yeah. They saw a quasar, and they saw this decrement, the Sunnih Vseldovich decrement, offset from the quasar at roughly the kind of scale. So it's a large scale of flow. This is how it's different from, you know, when stars form in galaxies, you know, you also drive little winds and so on.

But those winds don't reach out to such large extent. So, you know, Mark Lacey and his collaborators at the National Radio Astronomy Observatory did this measurement. And they did a very careful and thorough job, right? So first you have to look to see that indeed there's a quasar that's implicated and that there isn't another sort of hidden cluster of galaxy somewhere, you know, hotball of gas that's actually doing this. So they looked at, you know, multivabilant data, and they looked very carefully, and they were able to isolate

and implicate this one quasar that's sort of driving this wind. and what is kind of really super exciting from the physics point of view is that we had predicted that these kind of bubbles should be fairly long-lived. And that quasars, you know, they blink, right? They have feeding episodes when they're bright and then they turn off. And so these bubbles, these ghostly bubbles should linger. And that seems to have been proven right, too. So estimates of the age suggest that these are kind of long-lived bubbles. So how do you feel about it?

Are you feeling, you know, you're walking around like, hey, see, I was right? Walking a little bit on air, walking a little bit on air, I have to say. I mean, I think this is like the first detection, right? I think what is super exciting about it is that our prediction is that there should be a lot more of these ghostly bubbles and that this might be a new way to find quasars that have kind of turned off, right? They have an on-off switch. And so we might actually start to find very distant quasars with this sort of. a bubble signature. So, you know, I've always been intrigued by the first black holes in the

universe. And, you know, so I think it feels really good. And I think that, you know, when I was younger, I used to take other kinds of risks, skydiving, climbing buildings. And then when I went to grad school, I cleaned up, and I started taking intellectual risks. So this is kind of really nice to see that this is sort of come full circle. Had you, I mean, 20 years is a long time. I mean, not in the History of physics, it isn't. But do you just forget about it for 20 years? Are you always sort of in the back of your mind that maybe this year someone? No, yeah, I wasn't actually watching for it year by year, but I did notice that when Alma went on and I knew that in about three years after Alma was operational, it should become doable.

So, you know, it's kind of watching to see. But, you know, I'm not an observer. So this kind of work would take a big dedicated team. And so I was sort of looking out, but I wouldn't say that, you know, I was desperately waiting or whatever. I knew that it would kind of happen. But, you know, I like this element of surprise and thrill. You know, we talk about physicists here. And most people think physicists are physicists are physicists, but there are the theoretical physicists like you.

And then there are the experimentalists who have to make the device to measure it, right? I mean, so you really had to depend on those folks to come up with something that could find the evidence you were looking for. Right. And so, but I think what's really gratifying, right, is to think that we live at a time, well, I feel lucky to be alive at a time, where you can propose an idea and people will actually take it seriously and go look for it, right? And want to validate it or no validate it. So, I mean, for me, that itself felt like a complete treat. Did you pop any champagne? Anything like that?

Yes. Yes. She was with my family. So I went to India right after I heard about this. I was in India with my family in December. And so we had a nice little celebration. And my parents were really thrilled that, you know, I had moved to intellectual risks from the other risks.

That's great. We're going to take a break. And if you have questions for Priya, our number is 844-724-8255. We're going to talk more about black holes. We're going to get an update on LIGO, the gravitational wave detector, that could allow us to hear the cosmic collisions of black holes. I want to get DePria's take on that. We're also going to bring in another scientist who works with LIGO to talk about it.

And our number, 8444-Sytock, 844724-8255. Freeing, stay around and talk a little bit more with us. Sure. Happy to hang around. I'm sure, because the LIGO stuff, new kinds of LIGO information may be getting everybody's attention. We'll be right back after this. this break. Stay with us. This is Science Friday. I'm Ira Flato. We're talking this hour about the black holes with my guest, Priya Narajan, professor in the Department of Astronomy and Physics

at Yale University in New Haven. And I'd like to bring on another guest now whose work sounds like something superheroes would do, squeezing light. It's a technique that will make the gravitational wave detector LIGO even more sensitive to the rumblings of distant black coal collisions. Nergis Mavavala is a professor of physics at MIT in Cambridge. Welcome to Science Friday. Thank you. We're good to be here. And hi, Priya. I know that you must know each other. Yes. Oh, we do. Yes. How long have you known each other? Probably for decades, right? Nargis, we've known of each other. I was an undergraduate when Nargis was in grad school at MIT. So I was an MIT undergrad, yeah. All right. Well, NERGIS, tell us about that.

Let's talk about, it's old home week. Let's talk about how LIGO works for people who don't know. How does it detect black holes merging? So LIGO has an L in it that stands for laser and an I in it that stands for an diaphragmiter. And those are two words that we can deconstruct. So the way that LIGO works in the simplest way to think about it is to ask what is a gravitational wave from a black hole do here on the earth? And what it does is it actually changes distances between objects. And so if a gravitational wave passed between, say, me and Priya, the distance between us would change.

And the way we measure that is by shining laser light into that space. So if I shown a laser light from myself to Priya and she was a good mirror and reflected it back to me, I could measure the light travel time, It comes back to me. If I have a good clock, I just measure how long it light took. Now, when the gravitational wave comes through, that distance between us would change.

It would get longer and shorter. And the light travel time would change, and my excellent clock would tell me that the distance between us changed, and therefore a gravitational wave is going by. But it turns out that we don't have clocks that are good enough to do this kind of measurement, because these gravitational waves are extremely, extremely faint. And so what we really do in the end is,

instead of having one laser beam reflecting off a mirror and coming back to the laser, we split the laser beam into two parts that go at right angles to each other. They reflect off mirrors that are four kilometers or two and a half miles away, and then they come back and they interfere. And it's that process by which one laser beam

acts as a reference to tell us how long the other laser beam took to come back that allows us to make this measurement. And a thing that's exciting, that's most amazing about this instrument is how accurate it is, right? I mean, it's crazy accurate. So the precision with which you have to make this measurement is that the mirrors of LIGO that are separated by kilometers, by four kilometers, typically move by 1,000 the size of a single proton as the gravitational wave goes by.

So for people who like to think in terms of really small numbers, that's 10 to the minus 18 meters. Wow. Poofed my head. I think this is the most precise measurement human beings have ever made, right, Nurgis? I like to think so. Well, let's move on to the next generation because, Nurgis, you're working on something called squeezed light, which could allow Liga to see even more of the cosmos? Yeah, so me and many of my.

my colleagues and students together, of course. We're working on this technology called squeeze light. And what it is, is essentially it's a somewhat exotic quantum state of light that we engineer in our labs to improve the sensitivity of LIGO. And so to wrap our heads around, you know, what in the world is squeezed light, we, the easiest way to think about it is that life, Light is a quantum mechanical object. We know light is made up of photons,

and therefore, it must be uncertain. Quantum mechanics tells us that measurements are uncertain. And so really what we do is, here's a nice way to think about why, you know, what happens in the LIGO measurement. Imagine, so we use the laser light, and the laser light acts like the tick marks on a ruler for us.

It's essentially the wavelength of the light light, the number of times per second that the wave has a peak or a trough tells us, acts like a tick mark on a ruler. Now imagine I gave you a piece of paper and I told you, and I gave you a ruler and I said, could you measure the length of this piece of paper? He would say, oh, that's easy. You'd put your ruler down, you'd make a measurement and there you go. Now imagine for a moment that the ruler, the tick marks on that ruler jittered about a little.

actually move ever so slightly slush back and forth. Now you try to make a measurement of the length of the piece of paper, and every time you make the measurement, your tick marks have moved a little bit, and you make a slightly different measurement. Which is the correct measurement of the length of the piece of paper? You don't know, because your measuring apparatus is jittering. Now it turns out laser light does that, and it does that because of quantum mechanics, not because we've made a bad laser, it's because quantum mechanics says it must do that.

So squeeze light is a way of getting around that quantum uncertainty. You can never fully make it go away, but what you can do, what quantum mechanics allows you to do is to take some uncertainty in the measurement that you're making and tuck it away into a measurement you're not making. So I'll give you a nice example. Imagine that your laser light was of a wave, and you drew that wave with a very sharp pencil. And now if you look very carefully as you zoom down into that, it will start to look fuzzier and fuzzier.

It won't look so sharp anymore because of quantum mechanics. And what we do when we make, you can imagine, in fact, as you get closer and closer to the piece of paper, that very sharp pencil line starts to look like you drew it with crayon or something thicker. And what squeeze light allows us to do is it allows us to make some parts of that wave that we drew pencil sharp as long as we make other parts of the wave very fuzzy. So if we make the peaks and troughs pencil sharp, then we would make the center of the wave very fuzzy.

And we do that in our labs precisely so that when we make the gravitational wave measurement, we measure the phase of the light, and we make that sharper than quantum mechanics would allow as long as the amplitude of the light becomes fuzzy. So you're doing what, like, like, with video people do, they enhance a photo, you're enhancing the wavelength, the wave picture. Yeah, except that, you know, we have to obey the rules of quantum mechanics. What happens in, you know, the way that the video folks enhance a photo would be the same as if I took my, the pencil that I used to draw my light wave and I just made it sharper

and sharper. Well, quantum mechanics doesn't allow that. Quantum mechanics says if I make some part of the wave sharper, I must make some other part of the wave fuzzier. And so, and that's the difference. Right, there's a trade-off, right, that quantum mechanics imposes a trade-off. Always. So, Priya, what is this greater sensitivity of LIGO going and allow us to see more of, better,

of what, different? I think it appears, right, that the universe is just littered with black holes. And, you know, these are the, these are tinier cousins of the ones that I like, right? So my windy, gassy, powering black holes are super massive. And what LIGO and the enhancement to LIGO will be sensitive to is sort of their lower mass cousin. So black holes that are, you know, from anywhere from 10 times the mass of the sun to 100 plus times the mass of the sun. I think these enhancements, right, this sort of improved precision would allow you to detect, A, these sort of black hole mergers that are happening farther out into the universe. So increases the reach of what we can detect.

But also, am I right, Nurgis, now that the event rate we expect when you're done with your squeezing is about almost one a day. I mean, we should start to see almost like one event on average. That's the expectation, right? For black holes, yeah. For black holes, it could be that much, yeah. Would any of these improvements allow you to actually zoom in on a black hole so you can get closer to the actual event horizon where all the good stuff is happening? You see what's going on. Yeah, so you can, you can, if it were nearby enough, that, you know, we could measure it in our instruments with high enough signal to noise ratio, then you would, what you would expect is that these very subtle effects of what's happening closer to the horizon, horizons of the black holes, would be encoded in the actual signal that we measure.

At the moment, our signal to noise ratios are not high enough for us to look with that kind of fine resolution. But in time, I think that will be very much possible. But I think, you know, Ira, the kind of like mapping, so this would be sort of indirect mapping that you would get out of LIGO, but the kind of direct mapping you want, right, is, of course, going to come soon, right? We've talked about this before, the Event Horizon Telescope that's going to map the sort of the light shadows right around the event horizon of the black hole in the center of the Milky Way. So that experiment, remember, is ongoing. And I think results are expected any time now, right? So that's going to be the closest that we ever get to a black hole.

Because all the LIGO black holes and even the supermassive black holes that are going to merge that we are hoping to detect with, you know, this sort of kind of apparatus L-shaped that NERGIS talked about, it needs to be in space for detecting the gravitational waves from supermassive black holes because they happen at a much lower frequency. And so we need this apparatus in space. And so the Europeans are planning a mission and NASA's part of it, and it's called Lisa, expected to fly in the late 2020s, early 2030s. And I think that, you know, we will be able to actually say something about the populations of black holes and get at some of the fundamental questions, like what masses of the first black holes and how do black holes actually grow. And the exciting thing is that, you know, when black holes actually merge, not only do they set up these transatlanticians.

in space, time that we detect as gravitational waves, oftentimes with supermassive black holes, because there is a lot of gas, they're gassy, you know, in gassy environments, we will see other accompanying electromagnetic signatures, right? So the gas will be churned around, it will glow, and we expect to see, you know, one very heavy-duty feeding episode just when they merge. So a lot of gas going in that should glow in the x-rays and the infrared.

So I think we have a lot of black holes in our future. That's good. Of the good kind, of the good kind, yes. Here's a listener, here's a listener question for you. What is Priya's advice, and I'll also ask Nurgis to chime in on this. What is your advice for women who feel like they're being discouraged from doing astronomy? Well, I think, well, I think you can count me and Nurgis, test cases, right? Just do what you love, and, you know, I think it works out.

Is there a glass ceiling for women, astronomers, and physicists? I don't think it's quite a glass ceiling, but, you know, there are obstacles, to be honest. But I just think that at this point in time, the awareness of all the sort of biases and stuff is really high, and I think the astronomy community is very open-minded. So I'm very, very optimistic. And I encourage every young child, girl, boy, whoever wants to do science and astronomy that just follow your passion. I'll add one other thing. I think I agree with everything Priya said. I think it's also very important.

We're the lucky ones in the sense that we've had a good path into science. I know many young people don't. And so the one thing I would say is to find your mentors and your champions, whether they're within your family or or within your school networks or friendship networks, find some one or a few people who will hold you up and support you as you make your way sometimes upstream and therefore you need these champions to help you through. Right, and I think this is absolutely important

and has to be stressed at. You know, at every stage in the career you need these people. And I think that's sort of what can be challenging. But for a lot of young people, right, There are many sort of enthusiastic teachers, mentors and professors in college who are very supportive. So, yes, find yourself people who will cheer you on and help you build confidence and help you help you to really understand that this is a passion and encourage you to follow it. Amira Fleda, this is Science Friday from WNYC Studios. One last question.

We're running out of time. So many questions people are phoning in. I'll try to summarize one major question people are asking, which is, is your understanding of black holes going to solve the problem of we don't know what 96% of the universe is made out of? Dark energy, dark matter. I mean, it's crazy, isn't it? We don't know 96% of the universe. I know, I know.

This is the paradox of cosmology, right? That we know so much, and yet we know so little. We don't even know what the dark matter particle is, right? which is almost all of matter. So I think that black holes per se, right, are a tiny constituent in terms of the budget, but they're really important in how they shape the universe. So, for example, because of the impact on space time,

we really hope that gravitational wave events can be used as, you know, sort of like standard candles, like standard light bulbs, and can help us map the geometry and the fate of the universe. So I think in directly learning a lot about black holes has the potential to impact a lot of the other open problems in cosmology. But, you know, in and of themselves, I think they're super cool and exciting. There gets. Super cool, exciting? Completely, completely.

And I think one of the things that people sometimes wonder is would LIGO be able to see, you know, dark matter, for example. And the answer is dark matter is very diffuse. It's spread out all through galaxies. It doesn't clump into compact objects like black holes or neutron stars, which is the only things we are sensitive enough to see with these detectors like LIGO and, you know, and Virgo. So that's one of the things we can't do is see dark matter, even though we'd love to be able to. But dark matter must be some kind of particle, right?

Yeah. A particle that we may need new physics? Maybe. I mean, we have some pet candidates. They are not being borne out as possible. These are looking hard, hard and deep for them. But, you know, I think the... I personally believe that a lot of the constraints on dark matter

might come indirectly from astrophysics, right, from the light bending that you mentioned. So although dark matter is lightly smeared everywhere in the universe, it clumps on galaxy scales and much larger scales, and that bends light, and we see that, that's gravitational lensing. And I think going forward with all the big surveys and telescopes, you have W first as a satellite that's going to measure the shapes and distances to thousands and thousands of galaxies, we should be able to say something deeper, more meaningful about dark matter. I'm hopeful that maybe we'll experimentally detect it, right? I don't know. There are many direct detection experiments.

We'll be watching for it and having both of you back to talk about it. Is that a deal? Absolutely. Malva Vala is Professor of Physics at the Massachusetts Institute of Technology in Cambridge. Arrugas, thank you for taking time to be with us today. It was a pleasure. Thank you. And Priya Nada Rajan is a professor in departments of astronomy and physics at Yale University in New Haven. Priya, thank you for taking time to be with us today. Thank you so much, Ira.

You're welcome. We're going to take a break and come back and talk about California's other big one. It could be a flood of biblical proportions, which has already happened once in the last. last 200 years, how climate change is increasing the chance of a repeat. We'll talk about it after the break. Stay with us. This is Science Friday. I'm Ira Plato.

The headline in a recent L.A. Times was worrying at best. Rare L.A. megastorm could overwhelm dam and flood dozens of cities, the article warned. That dam is the Whittier Narrows Dam, which overlooks the town of Pico Rivera, east of Los Angeles. And that megastorm is a hypothetical 1,000-year flood like the 45-day deluge that drowned the state in 1861, the worst disaster that many people have never heard of. A new analysis from the U.S. Army Corps of Engineers found the Whittier Narrows Dam would be unable to handle the 36 inches of rain that fell in 1861, and its upgrade has been made the highest priority of any project in this country. A failure of the dam could affect up to one million people in the region. Here to explain more about, we'll explain more about that, is Lewis Hagen, a staff writer for the L.A. Times. He reported on the story. Welcome, Lewis.

Thank you for having me. You're welcome. And now your story starts with this new analysis from the Army Corps. What exactly are they concerned about in Los Angeles? us? The situation at Whittier Narrows Dam actually underlines how climate change has suddenly become an urgent local safety issue in Southern California. The spillway and the earth and dam were built in 1957 by the Army Corps of Engineers to control flooding and store water along the San Gabriel and Rio Hondo Rivers. By the way, they're about 13 miles south of downtown Los Angeles. Its construction was an urgent need at the time, and it displaced hundreds of people, including those in a farm workers' camp, where my family lived at the time. And I'm actually old enough to remember the commotion caused by the federal government's order for the

Mexican-American families there to leave the area. Today, that dam poses a serious risk to more than a million people who live downstream in 25, mostly working-class cities. Most of the year, that 56-foot-tall, three-mile-long dam contains little water. But the Corps recently classified it as the top safety issue in its system of 700 dams nationwide. That is because. So they're saying the dam needs to be upgraded ASAP, but they need money from Congress, right? Is the core assured of getting funding from Congress for this project? My understanding is that it is, and it needs roughly, well, up to $600 million to make the needed repairs.

That's because its engineers recently found that the dam would fail if water were to flow over its crest or if seepage eroded the sandy soil underneath. Also, unusually heavy rains could trigger a premature opening of the spillway, releasing more than 20 times what the downstream channel could safely contain. Now, in the Army Corps' worst-case scenarios, which are derived from computer modeling, estimating the risk during a 900-year storm event, downstream cities such as Pico Rivera, which has a population of 63,000 people, would be hit with water 20 feet deep, and their current evacuation routes would be turned into rivers. So what's this? Go ahead. No, I'm saying you have outlined the incredible risks. How soon could the, you know, renovation be made?

What are we talking about here? Yes. On Wednesday, Representative Grace Napolitano, whose district concludes many of the downstream cities in question here, urge the Army Corps to make safety repairs at footier narrows its highest budgetary priority. The Corps is expected to get the money it's asking for, the $600 million from Congress, and complete the job by 2026. In the meantime, downstream communities are only just beginning to revise their evacuation plan, revise the evacuation plans. And researchers are suggesting time is running out.

Well, I want to thank you very much for taking time to explain it to us, Lewis. Thank you. Louis Ahigun is a staff writer for the L.A. Times in Los Angeles. I want to continue on to the bigger picture. These major flooding events are more likely to happen as the climate warms. But according to research from my next guest, they were also already more. likely than we thought. And the problem isn't just one for Los Angeles, but the entire state of California. Dr. Daniel Swain is a climate scientist with joint appointments at UCLA, the National Center for Atmospheric Research, and the Nature Conservancy, and he joined us from Boulder, Colorado.

Welcome to Science Friday. Thanks so much for having me. We've been referring to this as the big flood of 1861 and 62. How bad was it, though? Well, it was a big one, and as I think you alluded to in the introduction, it's one of the greatest California disasters that most Californians have never heard of. And that's partly because it happened when California was a relatively new state. The population of the region at the time that this occurred last occurred in 1862 was about 400,000, compare that to 40 million today. So the state was a very different place. And yet even then, this was a massively destructive event. And it wasn't a single storm.

It was actually a sequence of what are known as atmospheric river storms that lasted more than a month and brought wave after wave after wave of rain pretty much to the whole west coast of North America, but focused on California. And what it ended up doing was resulting in catastrophic inundation of almost all of what are now, California's most densely populated areas, the Los Angeles Basin, Orange County, the San Francisco Bay Area, and the Central Valley. The Central Valley in particular was very hard hit and essentially turned into an inland sea, 200 miles long, 30 miles wide, and in some cases 20 feet deep. So this really was a fairly monumental event in California history. And it's been called the 1,000-year flood, but new research says it could happen.

more often than every thousand years? Yeah, this was actually some of the motivation for the study we did last year, where there had previously been this expectation than what happened in 1862 was essentially a vanishingly rare or unlikely sort of freak event. But it turns out that work conducted in the 2000s, especially by UC Berkeley researchers, suggested that the flood deposits in some of California's coastal river, systems suggested that floods equal to or even greater than what happened in 1862 occurred

multiple times per millennium. So really, every 150 to 200 years, so rather than being a thousand-year flood, it was really somewhere more like a 150- or 200-year flood, meaning that it happens five times more frequently than we used to think. And so even if we don't address the climate change question quite yet, these kinds of events are probably more common than we used to think they were. And let's talk about the causes of all this rain. You mentioned something called an atmospheric river.

Tell us what that means and how it forms, where it comes from, where it goes. So an atmospheric river, it's a very evocative term, but it actually evokes essentially the correct sense of what it is. It really is a river in the sky, in a sense. It's a river of concentrated atmospheric water vapor that looks, if you look down on it from space, kind of looks like a sinuous meandering stream, much like you'd have with a stream on land. And this plume of moisture in the atmosphere can sometimes attach itself to a winter storm system. And when that happens, that storm system can squeeze out a very large fraction of that water vapor in the atmosphere as precipitate.

over land, particularly in California's coastal mountains. And the amount of rain that can fall from these storms, these atmospheric river storms, is very much comparable to landfalling hurricanes and the East Coast or the Gulf Coast of the United States. So they can drop easily 10, 20, or even more inches of rain over the course of just a couple of days in the coastal mountains. So they can be massively productive and rainy systems that can produce, very large flood events. In fact, the vast majority of major flood events, not just in California, but along the entire Pacific coast of North America, are the results of atmospheric rivers. So you have this river that sort of, I'm picturing it, actually, in the story that you did, I'm thinking of a river that's actually a certain number of miles wide, certain number of miles deep, it stretches out into the Pacific and then carries all this moisture and just flow. flows into California and drops all that rain there.

That's essentially correct. These atmospheric rivers are usually a couple hundred kilometers wide, but can be a couple thousand kilometers long, and they can carry in the air above your head as much as 20 times the water that's in the Mississippi River at the mouth in the Gulf of Mexico. 20 times? It's a phenomenal amount of water. And it's all in the form of water vapor above your head.

So it's really kind of amazing to think about. And is global warming going to exacerbate this? All available evidence suggests that the answer is yes. And this is one of those cases where there's actually pretty high confidence because model projections are consistent with observations, which is also consistent with pretty basic theory. And that basic theory is simple enough that I'll just take a moment to explain it here. Essentially, as temperatures increase, the amount of water vapor that the atmosphere can hold increases exponentially.

So even as temperature increases relatively slowly, the amount of potential water vapor in the atmosphere increases much faster than temperature. So as you evaporate more water, you allow for the ceiling or the upper limit on the amount of moisture in these atmospheric rivers to increase. And so you don't necessarily increase the amount of precipitation all the time, but you definitely increase the maximum potential precipitation that can fall out of these sorts of systems. I'm Ira Flato, and this is Science Friday from WNYC Studios. Talking with Daniel Swain, climate scientist. You know, here in California, you visit California. I'm in San Francisco where everybody talks about waiting for the big one,

and they mention the big one is going to be an earthquake. But you don't hear many people talking about the big one being a flood that could fill up the Central Valley. Are people beginning to talk about it? Yeah, I think the comparison to the earthquake hazard in California is an apt one. And actually, the contingency planning exercise conducted by the U.S. Geological Survey in the state of California a few years ago, actually referred to a repeat of an 1862-like flood in California as California's quote. quote, other big one, the original big one being a large magnitude earthquake. And the state assessment essentially found that a repeat of the 1862 flood could actually be economically and in terms of the statewide disruption far worse than a large earthquake in Los Angeles or San Francisco and could cause upwards of three quarters of a trillion dollars in damages.

And that's a pretty sobering statistic. And the other really sobering aspect of this is that a lot of these damages would occur in California's most important economic regions, the Central Valley, where there's so much agriculture, the San Francisco Bay Area, where Silicon Valley generates so much economic activity. And, of course, Los Angeles region, home to Hollywood and lots of other industry, all of these places are locations that would be very hard hit. So I think there is increasing interest in recognition in the hazards posed by a really big flood event. But I think in certain circles it's still overshadowed by other risks. Everyone in California knows about earthquakes, and many people prepare seriously for them. Increasingly, people are really aware of the wildfire risk, and that's an awareness, I think, that has grown due to some really tragic events in the last couple years. but we don't have as much recent experience with these really large flood events.

And I think that does mean that it's a little bit more abstract for a lot of people than some of these other risks that we're more familiar with. I think what might make it abstract to people is that we just came out of a huge drought in California, right? And now we're talking about a huge flood in California. Is that the future we go from one extreme to the other? Yeah, it's absolutely the case that California has recently had a lot of drought and a lot of wildfire, so scarcity of water has been more in the news than over abundance. But that is, in fact, what we expect California's future to look like,

where even if we don't see a tremendous change in the average annual precipitation in this part of the world, we do expect to see increasingly dramatic swings from one extreme to the other, from very wet to very dry conditions and then back in the other direction. And that does present some real challenges because it suggests, first of all, we don't want to focus too much just on that average precipitation metric because it's not really telling us much about what's happening a lot of the time with the drought and flood risk. But it also means that managing water scarcity or managing flood risk becomes more challenging because we have to deal with ever greater extremes on opposite ends of the spectrum. And this is essentially the future that we expect to see in California, warmer almost all of the time, but both simultaneously wetter in some years and drier in others. And when you say challenging, that means the M word money, right? How do we prepare for these extremes?

It's certainly an expensive challenge to address, but it is also practically speaking. Even to know in the ideal world where money was no object, exactly what we would want to do. Because some folks say, well, of course, the obvious solution is to build more big dams to store more water in the wet years. But there's a number of issues with that approach, one of which I think is sort of highlighted by the risks we're currently talking about in terms of the risk of catastrophic failure of some of these big, important pieces of infrastructure given a big enough storm. All right, so we'll have to leave it there. We're out of time. Daniel Swain, Dr. Swain, is a climate scientist with the Institute of Environment and Sustainability at UCLA. Thank you for taking time to be with us today.

Thanks so much for having me. You're welcome. BJ Leatherman composed our theme music. Our thanks to audio engineer, Jim Bennett, and all the folks who made our stay very pleasant here at KQED in San Francisco. If you missed any part of this program or would like to hear it again, you can subscribe to our podcasts. Podcasts. You can ask you smart speakers

to play Science Friday. You can hear Science Friday any day you'd like. And, of course, we're always active on Facebook, Twitter, Instagram, all the social communities. Have a great weekend. I'm Ira Flito in San Francisco.