[00:00:00] Bridget Scanlon: Welcome to the Water Resources Podcast. I am Bridget Scanlon. In this podcast, we discuss water challenges with the leading experts, including topics on extreme climate events over exploitation and potential solutions towards more sustainable management. Hi everybody. Delighted to welcome Mike Dettinger to the podcast.
Today we are going to be talking about droughts and floods and atmospheric rivers in the US, particularly in the southwest US. Mike is a Senior Research Scientist at Scripps Institution of Oceanography in the Center for Western Weather and Water Extremes, and I think this is important these days when we are subjected to so many extremes.
He's worked there for the past 25 years. And, looking at Mike's background, his degree has really set him up for this job with a master's in hydrology from MIT and PhD in atmospheric sciences from UCLA. Mike is recognized for his research and received numerous awards and honors, and I think the most recent was being inducted into the National Academy of Engineering.
And the citation for his induction was for “hydroclimate research that significantly enhanced the understanding and management of water resources in the Western US.” And I think that really captures Mike's contribution to hydrology and climate science. And we'll see that throughout the podcast. Mike is also a fellow of AAAS from 2018 and fellow of AGU since 2014.
So thank you so much Mike for your willingness to participate in the podcast. I really appreciate it and I'm a huge fan of your work and so hope we can share that with others. Thanks for having me on. Right. So I mean, everybody is aware of the droughts in the US and particularly in this past year in the Western us, and many regions in extreme and exceptional drought.
And maybe you can let people know what you think of these droughts, precipitation impacts, temperature impacts and those sorts of things.
[00:02:12] Mike Dettinger: Sure. Well, we're entering what may be the fourth year of another drought in California. And California has this wide range of hydroclimates of precipitation, and as in its, has the widest range from year to year in precipitation of virtually anywhere in the US.
And this current drought is another expression of that. It's been pretty dismal in terms of the precipitation totals for the last three years. And so we, we would be in a drought in any event right now. But the most notable thing, I think my bias right now about the current drought is that it's also, this is also, a very warm period.
The whole globe is warming. Well, California's, feeling that too. And right now, this particular drought is particularly warm. And what that does is it increases the What we tend to call the thirstiness of the atmosphere over California to a great extent of it. For every drop of precipitation, it falls from the sky, more of that water tends to get sucked back up into the atmosphere before it shows up in our reservoirs and in our plants and things like that, such that it's been warm enough that, not this, not this past summer, but the summer before, what we call the evaporative demand. That's what I mean by thirstiness of the atmosphere, was the largest it's been in the time period where we've really got records of that.
It's the very thirstiest summer and full water year that we've had back to more or less the beginning of the, the satellite era, which is about 1980. So over the last 40 some odd years. Last, again, summer to summer before was the warmest. This past summer was right up there next to it in terms of how, how thirsty the atmosphere's been.
And this is, well our previous, most recent previous drought was in the 2012 to 2015 period, and that was yet another warm, really warm drought these days, it's hard to find the years when temperatures aren't right up there in the top 10 and historically, and that one was, also a very thirsty drought.
By contrast, if I look back to something like 1987, that the drought in 1987 or the really big, a really big historical drought in California, 1977, we had very little precipitation as little as we're seeing now back in those couple of years. But the thirstiness and temperature, the temperature and thirstiness was way down.
And so we really are seeing droughts that are as bad as we've seen in the whole record back 120 plus years. Now, if you're counting just how much of a precipitation deficit we're experiencing, but added on top of that is this extra evaporative demand that just turns what little precipitation we get during these periods into evaporation, more or less right back up into the atmosphere. So we'll get very little benefit from even the little bit of precipitation that we that we're getting. So I mean,
[00:05:58] Bridget Scanlon: it seems like we always focus on the rainfall amounts and things like that, but really I think more and more now we're starting to recognize the temperature is a big factor in how bad the droughts are.
And and so it seemed like California has hardly gotten a break. I mean 2012 to 20 through, I mean 2016, 2017, it broke and then you only had a couple of years of wet and then you're back in drought again. And, around 2000. Some people are calling these like mega droughts.
I mean, Colorado River Basin, those reservoirs down in the dirt, so it's really widespread and continuous almost since about 2000 right? .
[00:06:41] Mike Dettinger: Right, right. California does have this wide range of precipitation. I mean, it's really not uncommon that all that uncommon to have years where you get almost twice as much as normal precipitation in California.
And we get year, other years where, we get down to 60% of normal and, and that sort of thing. Whereas in most of the rest of the country, virtually the rest of the country, that swing, that range of swings is much smaller. And I mentioned that because what we're looking at here is that in the, as you move further into the interior west in over to the Colorado River Basin, and as you say, they've been more or less in drought with just a couple, you know, a little bit of relief once in a while for the past 22 or more years. And, and that is, I don't think you can, can live and work in that area without really feeling like this is more or less one drought that's lasted 20, 20 plus years in California. As I said earlier, we've got this wide range of precipitation that just happens naturally here in California.
And so in California, I know there are a lot of people who will, who feel that we've been more or less in a drought period since around 2000, but, in California, even our droughts are sort of set on onto this background of really wild highs and lows of precipitation. We have had years, like 2017, that was by some measures the wettest year on record, smack in the middle of the recent droughts.
And so, here it's a little bit harder to say, oh well it's been a continuous drought all that time. But that's just because we do get these occasional years when the storms really line up and just come plowing in one after another. And those are now little, those provide relief to the droughts.
To the long-term drought, but, well, yeah. At this point we're getting by, the only way we're getting by is if we're lucky enough to have one of these major wet years show up in the interior in the Colorado River Basin. They're not even getting that much of that. So they really are tanking.
[00:09:15] Bridget Scanlon: So it's, it's really challenging for water resource managers, I mean, one year of drought they could probably readily accommodate, but multiple years of drought then it becomes more problematic and more difficult for them to manage. And then, the wetter years then, so we either have too much water or no water.
And so really storing water then becomes one of the approaches to manage those temporal disconnects. But one of the things, when we're in the drought, we think we'll never get out of it. And when we're in a wet period, we think we'll never be in a drought again. I think some of that is kind of biased to view that we have, when the soil is dry and we think that the rain is coming from the soil and the impacting the rainfall, but maybe we should be looking at more larger scale things.
I think from your atmospheric knowledge and stuff that we shouldn't be constrained to thinking about basins and aquifers.
[00:10:10] Mike Dettinger: Yeah, especially on the west coast, California, Washington, Oregon, our precipitation comes essentially entirely from storms that form and below in, below, below a shore from over the North Pacific.
It's almost, it's virtually entirely that, and, if it's, if there's enough water around to evaporate back up into the atmosphere and the like, it's number one, have a relatively small addition to that, to these storms that blow off the Pacific. They've had 10,000, yeah, 8,000 miles to get as much water as they would ever want or need as they come across the North Pacific to the US.
But as you move inland, are still carrying most of that water that came from the North Pacific. our estimates are that for, if you look at an individual storm that blows in off the North Pacific, by the time it gets past the Cascade Mountains or to Sierra Nevada mountains, which are sort of where we get a lot of our water rained out or snowed out of these storms, they typically will have extracted the mountains will typically have extracted maybe 25% of the water that was in the storm.
And so now whatever evaporation you might, from California or Oregon and the like, is typically a relatively small addition to that off the Pacific Ocean. And it, you know, continues to get rained out as you go further and further inland. And so the storm, the air and the storms have finally done a lot of drying out about the time that they get to the, Midwest, to the Great Plains and places like that.
And there you start to see places where this feedback or, or, or local recycling of water where evaporation from the land surface and vegetation and the like, actually can start to dictate where and how much precipitation you get. But over here on the west coast, we're really at the mercy of, of what's happening over the, the ocean, over the Pacific Ocean.
[00:12:47] Bridget Scanlon: You have done a lot of work analyzing these droughts and wet and dry climate cycles, and you've written, I really enjoyed your paper in 2013 on drought busters. So maybe you can describe what typically breaks these droughts and, what happens and, how our understanding of those systems has evolved.
[00:13:06] Mike Dettinger: So yeah, so on the West Coast states specifically, we get, well, almost by definition we get, we get as many droughts as, as any place else. And by when I say by definition, I mean, you know, because we define, define a drought in terms of what we expect locally and when, how much less than that you have to get locally before you call it a drought.
So, we get the same number. The paper in 2013, what I did was look at what happens to break the droughts. To bust the droughts. And what I found was that there's a strong tendency for droughts in the west and to basically end relatively suddenly, which is a clue to what's going on.
It turns out that, when I looked across the whole US, this is true across essentially the whole US also, is that our droughts tend to end over the course, historically tend to end over the course of one or two. , you know, you'll go from pretty serious drought to Okay, we're pretty normal or we're even wet, but on the west, well, and, and, and, again, a clue it turns out also, furthermore, that the way that droughts happen, well, the way that droughts start is a much more gradual process.
It takes normally, historically it takes, six months or even more of less than normal precipitation and, and like to gradually go into droughts almost anywhere in the US and what's going on, what all this is pointing at, and what we find when we look is that what's going on is to get into a drought historically, the storms stop coming to precipitation, stops coming for a while or, or comes less than normal for a while and that sort of thing. And we don't, in most of the country, we don't get all of our precipitation, all at once. And so in order to build up a big enough precipitation deficit to declare a drought, it takes months and months of precipitation deficit, a typical sort of situation and again, analyze this in what are called climate divisions all across the country. And this, this was, really very much what happens across the country. This business of droughts ending abruptly is a reflection of the fact that, that, you ca well while your overall precipitation can, it's sort of spread out and, and you have to sustain a lack of precipitation in any given month, typically not enough to throw you into a drought. Then you can get enough precipitation in a single drought, I'm sorry, in a single month or a month or two to really to blow you out of the drought and into a better situation. That's why we, you know, there's a drought onward. We're watching the horizon, hoping for some sort of storm to show up and bail us out in California and on the west coast.
That's particularly true because we do get really whoppers, really huge storms sometimes, and they are enough to turn everything around really quickly.
[00:16:41] Bridget Scanlon: I think I, I think, yeah, I think the biggest example of that that I saw was looking at the time series for the US Drought Monitor for California, and it seemed like in January, 2017, from one day to the next, the drought ended.
That's all, that's all phases of drought, extreme, exceptional, and everything gone. Right. You know, and that was amazing.
[00:17:01] Mike Dettinger: Yeah. The the drought monitor is based on all different kinds of observations and reports of how much precipitation has fallen, how dry the soils are.
So if you go down the list, there's almost anything you can think about in terms of what a drought is. How you would recognize a drought literally gets tossed into the mix because it is, the drought monitor reflects a lot of data, but it also is based on the opinions of a lot of experts in each little part of the country.
There are phone calls going on every week literally of the experts to decide, well, where should we,where should we, how far should we say the drought has extended at this point? And yeah, and a winter, like 2017, well, I mentioned earlier that our previous big drought was in 2012 to 2015.
That was a real nasty drought, real deep in terms of precipitation deficits. And in terms of the surplus is of these evaporative demands that we are both demand side and supply side and the demand side we're trying to, pulling us into drought and, and holding us there. In 2016, we had in California we had a relatively normal precipitation year, but these days, especially when, when you're in a drought, a normal precipitation year just sort of keeps you where you are in the drought.
It really does relatively little to bail you out. And so we entered 2017, it was a dryish fall and so it really was, we were. Well, heck, some of my colleagues and I, you know, hurried up at that point for a variety of reasons and published a little paper about, okay, how are we gonna define what we call snow droughts? Because it's like, okay, we're still in this drought. It's time, when you're in drought research publish about droughts, and it came out in, in like in the January issue of the EOS that the American Geophysical Union publishes. and by the time it came out we had had the first of these major storms that we call Atmospheric Rivers show up the first one in a long time. And as you say, everyone was like, oh, oh wow, the drought's gone. That's always a dangerous thing because it's real easy to fall back into droughts. But yeah, I mean, look at, we're having to deal with the fact that there's an awful lot of water around. Too much water's starting to be the problem.
And then couple weeks later, another major storm blew end in, in early February, and that was when, I mean the central, the Sacramento Valley in Northern California was really pretty much wall to wall water. There was, it was flooding all over the place and everyone was watching their dams and their levies and all that worrying that they were gonna be overtopped or, or broken through.
And that's when there was a major crisis at the Orville Oroville Dam in Northern California where some 180,000 people had to be evacuated from their homes because they were downstream of the Oroville Dam. And things were really, the spillways were just being ripped apart by all the water that was, that was being flowing down them.
And that all happened. And yet the break in the drought was, as you say, it was just, over a weekend. I mean, literally it was over a weekend that the drought broke. And in February it just, we all knew that it was looking scary out there. And then in February, the big storms showed up and it got incredibly more scary in terms of possible and actual flood damages and all.
[00:21:06] Bridget Scanlon: So you, you brought up the term atmospheric rivers, and that term hasn't been around forever. When, when did, you guys start to understand what atmospheric rivers were and, and their impact on droughts and stuff?
[00:21:21] Mike Dettinger: Yeah. Atmospheric Rivers are really, yeah, I'm, I'm biased, but they're, they're one of the most exciting things going on in the arena of of meteorology on virtually a global scale and in many parts of the world in terms of hydrology and what an atmospheric river, well, I should say what an atmospheric river is, is, it turns out that something on the order of 90% of all the water vapor that moves around in the atmosphere outside of the tropics, Something like 90% of that vapor movement occurs in what in narrow, long, narrow bands, a really intense water vapor transport. So basically you want to picture this as a big fire hose in the sky and there are, half a dozen to, well on the, winter side of the equator. Depending on what time of year, what, what the month of the year is.
On the winter side of the equator. Have something on the order of eight to six to eight of these, these fire hoses. Moving water around with relatively little movement of water vapor in between them. And they're sort of distributed around the globe and they're there. Yeah, they're always about six to eight of 'em on the winter side and, more like four-ish on the summer side of the globe.
And they don't stay in the same place. They're always moving around. Basically, they're always sort of moving from west to east around the globe. And they will form, they'll kind of start to form someplace, and then they'll get more intense and more intense, and then they'll start to erode or, break down and they'll get weaker and weaker until they basically stop being something you would consider what we call an atmospheric river.
Atmospheric river, because they really are intense. They, they are rivers of water vapor and they are typically on the order of 500 to a thousand kilometers across. But they're, we don't even consider or don't mean get into, consider them an atmospheric river unless they're at least 2000 to 4,000 kilometers long.
And some of 'em get to be like 10,000 kilometers long. That will hit the, you know, west coast of the US And if you have a 10,000 km long river pointed at the west coast of the US. The, the beginning end of it is clear over, by Japan or something. So they're coming clear across the whole North Pacific to smash into the west Coast.
And so we have these big important in terms of the global water cycle things out there, and you would think that we would've known about 'em forever, but turns out that, nobody was paying that much attention to 'em, or even in some ways knew that they existed until 1998. I mean, there's really , there are a few things in science where you can point at a particular year and say, bam, that's when we figured it out in, in 1998.
Three different really important discoveries basically were made and and they were disconnected. They were not connected. Independent people working in different places discovered different things that when we took 'em all together, came together to our understanding of, oh, these atmospheric rivers are a big deal, and they're what we should be paying attention to.
So what went on in 1998, a couple of researchers at MIT, Zhu and Newell were looking at a long series, long sequence of weather model based forecasts of weather around the world, a global global weather forecasts weather as opposed to climate weather forecast that just accumulated a whole bunch of weather forecasts and, and looked at them to really try to understand among other things what the water cycle, how it kind of worked in this weather forecast model, These forecasts are a major component to the weawther forecasts that you see on, on TV every night, that sort of thing.
But for the most part, people focused on each forecast in isolation, certainly. Okay, what's it telling us? It's gonna happen tomorrow and the next day and so on. But Zhu and Newell got a bunch of 'em, and were looking at them in considerable detail over the long haul and what they've figured out. And yeah, and also at a global scale, they weren't just looking at what's gonna happen in San Francisco tomorrow? And, and so they looked at them and what they noticed, one of the things that they noticed was the business that I mentioned earlier that turns out that, 90% or more, I think they came up with about 95% was their particular number of the water vapor transport, heading generally poleward, so North, the Northern Hemisphere and South and the South Hemisphere. On any given day. On all given days. Put it that way, was concentrated in these funny narrow bands that, and you know, with all the work of getting vapor sort of up and moving it through the atmosphere outside of the tropics was, was for some reason just, concentrated in these bands that, that, as I said earlier, they, they move around. It's not like there's, some particular place where all the vapors has to go, they move around. But on any given day, if you go through and add up where the vapor is moving, it was always concentrated in these very narrow bands, narrow by meteorological standards bands, and long narrow bands, and they call it, they were the ones who coined the term atmospheric rivers as it happens.
(2) That same year, was in some ways a culmination of a process of getting to global coverage of a particular satellite, particularly kind of, satellite imagery of the earth based on microwaves. And you might wanna think in terms of radar, but it it based on measuring microwaves coming out, coming towards this, from the surface up into space.
And one of the things that you can measure with this, is its this microwave imagery is the total amount of water vapor in the atmosphere from space where the satellite is all the way down to the surface. And so they get back a number that is, oh, there's five centimeters of water vapor.
If you took all the water vapor in the atmosphere below this satellite at this moment, condensed it down, you would have, you would fill a cup to about, five centimeters deep of liquid wood water. And what had been going on is that the first of these s so-called SSMI microwave instruments had been put into orbit a few years before.
And, and they kept adding more and more. And by 1998 we finally had coverage such that on, all, every day we had a global coverage of the total mon one wow amount of water vapor in the atmosphere on about a 25 kilometer grid, all, all around the, the globe. And so now we could sort of put together these daily maps of water vapor in the atmosphere from the the satellite system, make movies of 'em and that sort of thing. But what it, maybe not surprisingly at this point, what they, what they showed was all the water vapor was concentrated in these long, narrow bands. And again, by the time we had a few months to a year's worth of it, you, it's like, and they're always out there.
It's not some odd thing that happens once in a while, always out there.
(3) And then the third thing that happened quite independently, just as the first two were, is that 1998 was one of the biggest El Nino's on record. And it was also the best. I think it'd be, I think it's still safe I believe it's still safe to say it was best forecasted one El Nino on record.
By 1997, we had a pretty darn good understanding of what to look for and how to predict whether or not the coming, there was a big one coming. And so by the summer of 1997, it was very clear that there was an Nino coming and that it was, looked like it was gonna be a huge one.
Very strong ao. So you had, you had like a lawn water down the tropics.
[00:30:47] Bridget Scanlon: Yeah. You had like a six month period then a six month forecast. Yeah. That's amazing.
[00:30:53] Mike Dettinger: And we're not used to having that sort of thing, quite frankly. And so one of the things that NOAA, the National Oceanographic and at Atmospheric Administration did was they really got out there to try and get people to understand that this was, this was coming and it was worth knowing about in many part, in the southwest of the US El Ninos are associated with the really wet years.
And so it's like, ah, not only is this, are we pretty darn sure you're looking at a wet year? But when we have in the past had these big El Ninos, they were really wet years, like 1983 was the sort of the case study of that. And so, NOAA was doing a lot to get people and, and water agencies and flood control agencies and all that to take this very seriously.
We're tying you this year. If you wanna get ready for a floody winter, you know you, this is the one you want to prepare for. It's coming. Anyway. Among them, things that they did was that arrangements were made to have scientific aircraft available. For some, for some NOAA researchers to fly out into some of these, some of the storms that imagined there were gonna be, some really big storms this, this coming winter.
And indeed they flew out in winter of 1998 to visit them and make measurements in them. You wanna think of this sort of like the hurricane hunters that we hear about every summer where they fly out and through the storms and make measurements and that helps to really get a handle on what, how bad the storm is and, and you know where it's likely to go and that sort of thing.
Well, they flew on out and just to really see what's going on in these major Pacific storms as they approach the west Coast. And what they ran into, they basically found that, wow, all of the water that's coming in these storms are, is concentrated in a narrow band, and it's a narrow band that they called a low level jet.
And it was, so it was about a mile over mile from the sea surface, kilometer and a half above the sea surface. But it was very much, the water that was ultimately going to make this, the precipitation when these storms arrived, were in these, concentrated, relatively low in the atmosphere.
I mean, consider that, that, when you're flying across this country, you're flying at 10 kilometers above the surface. And so, these things are more like a kilometer and a half. They're way down there though. And the upshot is that they fall through enough of that, of the storm, back and forth, that sort of thing to say, see that, oh wow, there, there's this jet, again, think of our fire hose.
This jet is sitting there, the long narrow jet slash fire hose, and they really, it's like, okay, wow. That's what's making this, these particular storms particularly nasty and wet once they reach the west coast. So all three of these. Very independent efforts. All were suddenly recognizing that, hey, you.
These long, narrow rivers of water vapor in the atmosphere are really important. And it frankly, it took a while to really understand, especially on the flying out and through the storms to become sure that this wasn't a fluke. This, this isn't some weird storm that just happened to have a strange shape, but that this is kind of how the big storms work that, that come off the North Pacific and to the West Coast.
And so it all came together, but as I say, it actually took about five years before, before all the pieces were kind of connected, these independent pieces were connected. And I'll give credit to the folks at, NOAA who really kind of pulled all those together and recognized that this thing that that Zhu and Newell at MIT had called Atmospheric Rivers were really a big deal.
So they had took until about 2000, well, it took until 2006 for us, and by now, I, I had sort of, begun working with the folks as their kind of resident hydrologist and climatologist as opposed to a bunch of meteorologists. And we asked kind of obvious questions in hindsight, but is, you know, how often, what's the relation between these atmospheric things showing up on the west coast and big historical, big floods on the west coast?
And we looked in the Russian River basin, north of San Francisco in California, and that happens to be about the funniest part of the West Coast. And and it turned out that, over the preceding, I don't remember what the numbers are now, but let me say about, well, it would've been 2006, so I don't previous 10 years, right there would've been about, there were seven declared floods, flows in the river that reached a level where they were declared by officially, this is a flood, this is a hazardous situation. And all seven of those sprung, strung out over the past 10 years were when an atmospheric river was coming onshore directly next to this Russian River basin.
And so it's like, oh, oh. It took us a while after that to sort of put together the stories, the time series and the like to be able to go further than just oh, 10 years, so now we can look back, 50 years, well, these days, 70 years. And, and what we find is that about 80%, across much of the west coast and certainly down to San Francisco, well, from Canada down to San Francisco and, and almost to Santa Barbara on the west coast, you're really looking at roughly 70 to 80% of all the floods are associated or, or occur when an atmospheric river arrives. So suddenly we had this one thing, this one storm type that you know contained yours in it. 80% of the flood risk. Story all, on the West coast, it, it's kind of phenomenal situation. We didn't, we don't have them anywhere. Yeah.
[00:37:45] Bridget Scanlon: I mean, that's amazing that all of those things came together. So the MIT folks with the modeling and analyzing the long term and more detailed, and then the satellite data, providing the global coverage of the integrated vapor transport so that you could map and you could see these atmospheric rivers. Right. And then I don't think I'd want to be the pilot on those planes, I mean, if they're only up a couple of kilometers and they're flying in and out of these storms, I mean, I think that must be kind of crazy.
[00:38:13] Mike Dettinger: But, It's a bit crazy. I'll tell you that unlike flying through a hurricane, which pretty much goes up through the troposphere.
Yeah. So you, if you're gonna fly through it, you're gonna fly through it. What? These atmospheric rivers, because they're so low, what they actually do for the most part, is they fly over 'em. Basically at a fairly safe distance to pull them. Right. And drop, drop, measurement, they call 'em drop zones down through them.
Okay. This is folks like Marty Ralph, who was in NOAA running the show for this kind of aircraft stuff. But then, moved over to Scripps where I was, and, and established the center that you mentioned earlier.
[00:38:58] Bridget Scanlon: So I guess you, you call them atmospheric rivers, and I think some people say average, maybe the flow of one of these, through the, one of these atmospheric rivers is similar to the Mississippi, at the mouth of the Mississippi, but then when you have a strong one, it seemed like they could be seven to 15 times the flow in the Mississippi.
[00:39:15] Mike Dettinger: Yeah, it, they are, well they're, they're closer to, sort of your average one is closer to five or 10. And, the big ones, when you've got a really strong one, you're looking at, at 20 and, and, and more times the flow of the Mississippi, five or tens times the amount of water that flows out of the Amazon.
These are, wow. Wow. These are vast amounts of water, especially when you, for us working in the, western US when you consider that we're really kind of living in a, in a relatively dry area, that's a lot of water, right.
[00:39:48] Bridget Scanlon: And so I guess, I guess then they hit the mountains and then, yeah, it, move up and then the water vapor condenses and you get, major, major rainfalls or snowfall or whatever, depending on the situation.
[00:40:00] Mike Dettinger: That's right. Yeah. They get, they, yeah, just like a, like a, again, back to the fire hose, spraying the fire hose. It hits the mountain, the front of the mountains and just gets squirt, gets squirts up, up into, gets lifted up by the mountain range themselves. The mountain ranges themselves and their cools and the water out of the air, and we, you get these really large amounts of, precipitation, like, especially from the big ones, the ones that are carrying the most vapor. Right? Yeah. I should say that, that among the, well among the, so prior to 1998, prior to about 2003 or four for that matter, we were aware that these things existed, that some of these things existed.
It'd be hard to miss something that causes major floods, but basically we knew them as Pineapple Express storms and that Pineapple Express is a cute way of saying that they, they on satellite images and the like, that you see this line of clouds that extends from roughly Hawaii area all the way up and, more classic Pineapple Express is pretty, really a straight line that goes from, over there by Hawaii all the way up and runs into the west coast and, we were aware of that. But the trick was, and, and in fact I, I was studying these pineapple expresses trying to understand a little bit about why, when they, why they happened, when they happened, and that sort of thing. You know, how often they happened. And, but turns out that, that an atmospheric, that a pineapple express is just one version, one particular form of, of these atmospheric rivers, which there are lots, lots more of them out there in all different configurations.
That means coming out of, coming from the north down in some bizarre cases, coming straight across the Pacific and, and wiggling. You know, they, they'll kind of bend as they come in to all different shapes and sizes, right? The pineapple, and. as long as I was looking at the pineapple expresses, I probably wasn't gonna get there because it's like pulling, a particular handful of, of coins out of, out of, a, a jar and, and trying to make sense of the situation when actually the, those coins are just a few out of a hundred in the jar. Once we started looking at the atmospheric rivers, we were looking at the whole range of things that goes on and, and the story starts to fall together. So yes, that's where you get this 80% businesses, right? Somebody started to say, Hey, wait a minute. Right?
[00:42:53] Bridget Scanlon: You know,and, and your analysis of the rainfall in the west coast, you indicate that maybe 30% of the rainfall in the south and then up to 50% or whatever, as you go further north along the coast towards Washington and stuff could be attributed to atmospheric rivers. And then your drought busting paper, you said, you know about similar percentages, right?
Of the droughts were ended with these atmospheric rivers. I mean, so that gives us an idea. I mean this concentrated rainfall over short time periods then accounts for a lot of the rainfall in these areas.
[00:43:28] Mike Dettinger: That's right. And, and the trick is, 30 to 50%, oh, well that, that's nowhere near as impressive as 80%, that sort of thing.
But the trick is that these atmospheric rivers, in California on an average year, we might get a dozen of 'em total, and only four of them, maybe might be four or five of them, might be strong ones that you would really drop a lot of water and have the potential to cause floods and the like.
So, in four or five days, in the year they do all this work of giving us 30% or 50% of the, of the total precipitation. And then, the trick with the droughts was to figure out in which months the droughts broke. When, when did the droughts end? And then go in and, I went in and looked at the daily weather and the daily precipitation and the daily stream flows in that month to figure out when exactly the storm that changed everything showed up, or, flows depending on how you were measuring your drought.
And then you turn around and say, okay, so what was going on on these days here that where the drought turned around and and broke. And that, when you do that, you find, oh crud, you know, 30 to 50% of the time it's way up to like 70 or 80% up, up further north on the west coast. Our droughts end with the arrival of one or two atmospheric rivers in the rapid succession that dump a bunch of precipitation.
And so, with floods we now have. Boy, ma'am, we know exactly what to look at. If we, if we knew what was gonna happen in terms of atmospheric rivers, we would know 80% of the time whether we were facing a drought was, I'm sorry, a flood would arrive. It's not quite that good.
But we now know what to look for in terms of the endings of droughts. And I gotta tell you, when you're in a drought and you're a hydroclimatologist, the question that you hear a billion times, a week is when's this drought gonna end? It's gonna end this year.
We're getting it now, we're, we're in the fourth, we're entering the, what could be the fourth year of this current drought in California? And the question, the question on everyone's lips is, are we gonna get out of the drought this year? Is it gonna turn around this year? At least now we know what to look for. So these atmospheric rivers have been really important to us.
[00:46:02] Bridget Scanlon: So, so I think, your 2013 paper, you said even if it's just 30% of the droughts end with atmospheric rivers, it seemed like all of the major droughts, like 76, 77, 87 to 92, all of these ended with atmospheric movies and strong atmospheric rivers, because that's what you needed to end the drought. That's right. You had to have a strong atmospheric river or family of them to end those big droughts.
[00:46:27] Mike Dettinger: As, as a climate and water scientist, you'll appreciate the fact thatyou would sell your soul for sample size, which is to say you need a lot. A lot of cases to look at, to really begin to understand how important or how reliable something is in, in sort of the earth sciences.
And so with that, that drought buster analysis that I did, I was very relaxed about what I would consider to be a drought, a serious drought. And in order to get my sample size, my number of cases that I was looking at, up to roughly 20, over the past 60 years, so, when you get more strict about it, and say, no, I really, I want things that everyone would've agreed were droughts, that everyone was in a panic over. Then as you say, you know, it really does for us, in California and, and as well as up the whole coast, our droughts, and when with the arrival of Atmospheric Rivers, and, and rarely any other way.
[00:47:43] Bridget Scanlon: And so I think that makes it extremely challenging for water resource managers then. But it seems like you guys are making some headway working with the managers and trying to adapt to these extremes. Either no water or too much water. Can you describe a little bit about this FIRO program forecast informed reservoir operations?
[00:48:05] Mike Dettinger: Sure. The good thing is once you figure out that there's a particular version or a particular storm type that is what you need to concentrate on in order to deal with 80 plus percent of the floods. If flood protection is your goal, it changes the entire, the whole game of forecasting. You know what to look for if you are strictly looking at how much precipitation your weather model pumps out on a given day.
You are at the mercy of the model. You're completely at the mercy of the model. It's, it's difficult because really at the mercy of the model and, and this whole business of as the story of these atmospheric rivers serve, unfolded, and we started to realize just how important they were. It was very natural for the forecast agencies, the weather service, as well as for researchers to start. They knew what to look for. They could look for these, these narrow bands of these atmospheric rivers, and they could learn to recognize them, to recognize the precursors to them and all of that. And so it just sort of focused the attention in ways that proved really, really useful. And it allowed for some serious improvements in the ability to recognize and to generally forecast these major storms that cause our West Coast floods.
And I, my favorite statistic these days interjected everywhere. I got out of one of, as I reviewed one of the reports that the Center for Western Weather Water Extremes was putting out last summer. Is that for, or the Yuba Feather River Basins, which are in the Sierra Nevada a ways, north and certainly east of San Francisco, just to sort of, they're in the Northern Sierra Nevada.
And what was done was that the forecasts over the past, I think it's back to about 1980, I think it was, of the times when major really intense ARs were forecasted to pass over and dump their precipitation over the Yuba Feather River basins historically were looked at, they looked at the forecasts, and then they looked at what actually happened, and the statistics that just blow me away. They explain why these things become, why knowing about these things become so useful is that of all the times when, strong ARs were forecasted to pass over the Yuba Feather River basins at three days ahead of time, 86% of the time it happens. They show up. That's, that's amazing. Yeah.
five days out, it, it only has dropped to 80%. That's still, yeah. Nobody forecasts 80% of the time. Right. So that's just astonishing. And in order to get to the breakeven point, where you know, it's like, okay, they say there's a big one coming. Should I, is it gonna show up? The breakeven point is where, I might, I could flip a coin and do as well. Okay. 50% odds is somewhat a slight around, a little bit over seven days, a full week out. Those three and five day statistics are just astonishing. And what. Well, those of us on the science side of this Atmospheric Rivers business have been working since, 2015 with the Army Corps of Engineers and some local, water agencies like, for the longest time, the Sonoma Water Agency up in, on the Russian River and the state of California and others.
Fisheries people and, and a wide range of people to really try and evaluate whether, I mean, one way of putting it is, whether this kind of forecast ability of AR driven floods and ARs themselves is accurate enough and useful now, you know, actually means enough to allow people to, well, to allow the reservoir operators to base their releases of water from the reservoirs during the wet season on the modern forecasts. And because these atmospheric rivers are so important, to determining whether there's gonna be a drought or a flood or not, and because we can forecast them with such remarkable accuracy once you know what to look for, and it's really a matter of what you know, you need to know to look for.
It turns out that indeed, on the Russian River basin now for Lake Mendocino, we've been oper, we've gotten to a point where we've been operating that reservoir. Actually, the Corps of Engineers has been operating that reservoir for the past several years on the basis. On a basis of modern forecasts, forecasts have been used by operators, by the folks who, turn the switches to allow water in or out of the reservoirs, for a long time.
But they've always more or less had to do it, kind of the down low it was against. In principle, it was virtually against the rules. Flood control reservoirs typically have set a very specific set of rules that's established for all intents and purposes by an Act of Congress. I mean, it's virtually that sort of thing that establishes exactly how they're operated and the traditional the normal way for nearly all flood control reservoirs around the country is called a rule curve, but basically it amounts to during the season when you are at risk of floods in California, it's in the winter wet season because during the summer we don't really get storms, and so typically we don't have floods In the summer, the reservoir operators are required to keep a lot of open space in the reservoir, below the top of the reservoir.
They have to keep a lot of space to catch any floods that happen to come come on down so that it doesn't just blow over the dam and flood people downstream. And so during the winter, once you get to flood control level, any additional water that comes in, you have to let out.
You have to hold it down to there. And so if a big storm shows up, you end up encroaching is the term for it into this, this flood control space. There's water in it now, oftentimes a lot of water, and they have to just let that water go. The catch is that later in the year, you really wish that water was there, that you could have kept that water safely because you're gonna need it for irrigation and for community water supplies and for fisheries and everything else.
And so there's always been this tension between keeping the reservoir water levels down so they can have room to catch flood flows versus keeping them full, So that comes summer. The way you've got the water there when you want it and need it. FIRO, this forecast informed reservoir operations is largely a trick with it, and I hesitates use term trick, but sort of the strategy that way, way down deep underlies it, is that, same imperatives, you still don't really want, you wanna have space to, capture flood flows. So they don't do damage downstream. But, again, becomes that with modern forecasts, weather forecasts and flood forecasts for that matter, we can do well, especially in a place that has atmospheric rivers so far because they allow us to recognize mm-hmm. way out on the other side over by Japan we can see, oh, there's atmospheric river forming time to get nervous.
The gain becomes one of, okay, so if the water, if we get a storm in and the water levels rise above that flood control line, should we, do we let it out? Well, under current management methods, in most reservoirs, there's no question you let it out. But with FIRO, what we're doing, one way of viewing it is that we're, we're saying, wait, before you let it out, let's, if we're at risk in the near term of, of another storm showing up and now overtopping flood flows, overtopping the dam or something like that. And it turns out that it's actually easier, more accurate to forecast when the North Pacific is largely devoid of these atmospheric rivers so that they're not coming your way. And it takes them typically, four or so days or, or up to a week to come across the whole North Pacific.
So you're not seeing anything out there, you know that, ah, you know, we're pretty safe, we're, we're very safe for three to five days to, that sort of number of days ahead of time. And another circumstances. You hold it for a day, you hold that, this extra water and then you look the next day and you are there any risks out there? No. We're holding another day and it comes this game of waiting until there's some risk out there and it's really a very low risk amount, way out there in time. Because the other part of it is that, okay, now we see a storm. Some storms start to form way out there, and they're headed to our way.
[00:58:25] Bridget Scanlon: What you do is you might have used the water. Yeah, yeah.
[00:58:28] Mike Dettinger: Right. You can look the water out. And so the trick, the other half of this trick is to know how many days, heads up, lead time do I need to have, how, how long does it take to get the water out of the reservoir safely? Right. So that I can get that done before that storm shows up. And so the, the Corps of Engineers and others in on the Russian River Basin, you know, have done a bunch of studies to figure out how long do we need? How much lead time do we need? And it turns out that if you've got five days worth of lead time, if five days before that storm's gonna arrive, you have enough time, start doing, letting flow out, then I can do it safely.
And it's not just that it takes five days to dump the water, it actually takes only a couple, two, three days to dump the water. it's more a matter of, you also want to make sure that when you're dumping the water, you're not aggravating some problem downstream. So if there's high flows downstream, that aren't quite flood flows, but are right there at the doorstep, and now I start dumping all my water, I could push those downstream flows into a flood situation, so, need that extra time. And, and it turns out that based on some very long experiments with what we call hindcast, which is using today's weather forecast and flood forecast models to make the forecast that we'd make with today's tools for every day since roughly 1980, and now we can use that and we can figure out that okay with, if we've got the five days, we're good.
And in, and as a matter of fact, what we discovered in these studies on the Russian is that for the Russian today's forecast, you know, the forecasts that are we're capable of making today are adequately accurate to allow this to work safely, even in the biggest storms that we throw at them. Right.
[01:00:38] Bridget Scanlon: Well, it's really a amazing, so I know the Corps of Engineers is working with managed aquifer recharge also, so they could move some of that water off into depleted aquifers nearby and store it there. So we're getting a lot more adept at trying to manage these extremes. And I think that's just an incredible story of how, the understanding of atmospheric rivers developed in the late nineties from the modelers at MIT and the remote sensing data and then the aircraft flights by NOAA and stuff, and bringing all that together and understanding these things and then their forecast, ability to forecast them and then combining that and working with the agencies to translate those advances in science to operations and management.
I mean, that is amazing. Yeah.
[01:01:29] Mike Dettinger: I've been in the game for a long time, literally 40 years, and, worked on a lot of these kind of issues before. But this, this business of the atmospheric rivers and what it's allowed us to do in terms of the science, the discoveries we've been able to make about these atmospheric rivers have fit more neatly and, and tightly with the actual operations, with applications than I, I mean, than any, any other research I have done, research I'm really proud of in the past.
But these atmospheric rivers have just been a total gift. They've changed so much about our understanding, but also about practical applications, resources, and floods are actually managed in the real world. And, and this FIRO business is something that is, kind of going wild right now. That Corps of Engineers is looking at reservoirs all over the country, starting to look at reservoirs all over the country to try and determine whether this sort of thing can be done safely anywhere else. It won't, there will be places where it can't be done, but the question now isn't, can this be done safely anywhere? It's how, how commonly might this be possible.
[01:02:51] Bridget Scanlon: I know they're looking at it in Texas, so we'll be learning from you guys. Well, I really appreciate your time, Mike, and just delightful to learn about these climate and hydrology linkages and how it works and, and of course, droughts and floods are on everybody's mind.
So really appreciate your educating us on these. So our guest today was Mike Dettinger from Strips Institute of Oceanography in the Center for Western Weather and Water Extremes. Thank you so much.
[01:03:21] Mike Dettinger: Thank you. This has been fun.
