Ep 45: Atmospheric Rivers

A conversation with Dr. Katerina Gonzales (EPA Climate Adaptation Advisor) and Dr. Daniel Swain (UCLA) about atmospheric rivers, climate extremes and futures, and climate science communication. Rereleased March 17, 2023 with original recordings from June 30, 2020.

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Mallika Nocco  

Welcome to Water Talk from the University of California Division of Agriculture and Natural Resources. I'm Dr. Mallika Nocco, a cooperative extension specialist in soil plant water relations and irrigation management.

Sam Sandoval  

Hi, I'm Sam Sandoval. I'm a faculty and extension a specialist in water resources.

Faith Kearns  

And I'm Faith Kearns, the academic coordinator for the California Institute for Water Resources.

Mallika Nocco  

Thank you for joining us on Water Talk. In today's episode, we're talking about atmospheric rivers and changing climate extremes with Kat Gonzales and Dr. Daniel Swain. Kat is a doctoral researcher at Stanford University. And Daniel is a climate scientist with the UCLA Institute of Environment and Sustainability as well as a fellow at NCAR (National Center for Atmospheric Research) and The Nature Conservancy. Both of them are, in my opinion, badass climate scientists. And they're also experts at science communication. And we're so excited to have them here today on Water Talk.

Faith Kearns  

We wanted to just jump right into the technical topics with technical people. So we want to talk a little bit about a term that may be new to some people, which is atmospheric rivers. Can you tell us a little bit about atmospheric rivers and their importance and the role they play in California's overall precipitation and weather outlook?

Kat Gonzales  

Yeah, totally. So atmospheric rivers are these plumes of concentrated atmospheric moisture. They look beautiful, so if you haven't seen one in the satellite imagery, go Google that and type in GIF at the end. So there are these features all across the globe, and they're very important, particularly for the west coast of the United States, also the west coast of Europe, and throughout the globe. But as we know, in the west, water is so important and our water resources are so important. And these features provide a huge proportion of our water supply actually in the form of snowpack.

Faith Kearns  

Great. Thanks, Kat. Did you have anything you wanted to add Daniel?

Daniel Swain  

Not much beyond Kat already emphasized other than to say, I think she mentioned atmospheric rivers, they're not a new atmospheric process. They're not a new phenomena. But the term atmospheric river is relatively recent and the more nuanced version of what used to be called the Pineapple Express storms in California -- which are still, by the way, a legitimate subset of atmospheric rivers -- but atmospheric rivers are sort of a broader descriptor for a wider range of events that don't have to originate from the subtropics near Hawaii necessarily. As Kat mentioned, these are super important from a water resource perspective. They're also super important from a flood risk management perspective, because they're simultaneously responsible for most of the water supply and most of the flood risk in a place like California, for example. 

I would just mention that atmospheric rivers, they are a global phenomena, but they're really only important in specific kinds of regions, usually along the west coast of continents in the mid-latitudes. So this is true of the west coast of North America, the west coast of South America, a small portion of both Northwestern and Southwestern Africa, small patches in southern Australia, as well as the Mediterranean itself. California is known for having a "Mediterranean climate" so perhaps that's not too surprising, but these are features that are really important in some regions, not so important in others, and are something we're really interested in, in a warming climate.

Sam Sandoval  

So perhaps elaborating a little bit on that one. Kat mentioned a lot of features, but what are those features? How did they actually look like? What they actually did -- rain or snow or I don't know, any more kind of descriptive details on that?

Kat Gonzales  

Yeah, those are great questions. So colloquially, they've been known as rivers and the sky, which I think is a great descriptor that anyone in the public can understand. They are literally moving water in the sky, it's just the form of water tends to be vapor. And these rivers in the sky can hold more water content than some of the major rivers in the globe. So truly rivers in the sky is an appropriate descriptor. Is it rain or snow? It's both right. 

Here in the Bay Area where I live, I can usually tell the atmospheric rivers happening because it'll just rain for hours and hours and perhaps even days and that's felt by me as rain. But in the high country where the precipitation is cold enough to fall as snow, then they experienced that as snow. And that's really important because we know our snowpack is important. That all has to do with, is it cold enough for it to snow? That was a big motivator for a paper out a year ago that looked at trends in atmospheric river temperatures, because we know that the globe is getting warmer and if atmospheric rivers get warmer then the precipitation is more likely to fall as rain rather than snow.

Sam Sandoval  

And I think those are, I mean, both of you have done these kind of different flavors of atmospheric rivers. So I think part of it is in terms of the temperature, could you elaborate a little bit more Dan or Kat?

Kat Gonzales  

Sure, yeah, I can tee off this concept called flavors of atmospheric rivers that I and others, along with Daniel, are working on currently. This work is in prep, but if you could imagine just an atmospheric river moving, that water vapor moving, that moisture transport, some parts of atmospheric rivers, not parts, but some of them have been described even by meteorologists as more wind-dominated or more moisture-dominated. And so that's what this current study is getting at is just really capturing that characterization, that distinction between these super wet, but perhaps not as windy, atmospheric rivers that perhaps may just stall, and super wind-dominated atmospheric rivers associated with surface winds. That's just one of those flavor continuums that we're describing here and there's so many different other characteristics in the literature. What else would you say about flavors of atmospheric rivers, Daniel? We've already mentioned pineapple flavored atmospheric rivers.

Daniel Swain  

I think would extend the terrestrial river analogy. You already mentioned that some folks sort of analogize these to rivers in the sky, which I think is entirely appropriate because some of them, as you mentioned, a good sized atmospheric river in California is usually bringing a flow of water similar to that of the Mississippi times ten during a particularly big event, and once again, that's all water vapor coming in above your head. 

But in terms of the flavors, I think the analogy might be, you know, there are two ways to get a lot of flow through your traditional river on land, right? You can either have a very wide, very deep, but perhaps slow moving and meandering river like the Mississippi, which is moving a lot of water over time, but maybe not in violent fashion. Or you could have a much smaller, much narrower channel with water that's moving extremely fast through that channel, putting through a similarly large amount of water to the broader, but more lazy, meandering river, essentially. And really that's similar to the kinds of flavors of atmospheric river that we're thinking about, where one is dominated by the really fast flow, the strong kinetic movement. In the atmospheric river case, those are the ones that have a strong wind component to them. 

Then in the other case, the slower meandering river would be more like the ones that have a huge amount of water vapor, but maybe not as much wind pushing them. So, you know, in the river case, obviously, the characteristics of those kinds of terrestrial rivers are very different in terms of the benefits they bring, the harms they can pose. Same thing is true with atmospheric rivers in the sky. You know, the really juicy, moist ones versus the ones that have super strong winds are going to bring different impacts. And they may change differently too in a warming climate. So it is important to be able to differentiate between the kinds of different flavors of atmospheric rivers because it really is consequential for what they mean on the ground in terms of the water from a water management or flood management perspective for sure.

Faith Kearns  

I'm just to ask a follow up question. I guess shifting gears slightly. You, I think, coined the term weather whiplash, and we were wondering a little bit about what you want to convey with that terminology and what it means for those of us living here and in the west in general?

Daniel Swain  

Yeah, well, I'll just say I'm not sure I'm not the one who coined that term originally. I think it was it was floating around out there before I did. But I think its application to California precipitation, specifically, I'll take credit for precipitation whiplash in California. But I think that the basic notion is that California already has a highly variable climate on a bunch of different timescales. Even if you just think about our typical seasonal cycle from winter wet season, well we effectively have a drought every summer. That is not the case in most of the world where there's a really well defined winter cool season, wet season and then you know, a long dry period every single warm season or summer, but that is what it's like in California. So you already have this strong variability in typical annual cycle in California. 

Then between years, you have very wet years in California and very dry years to a much greater degree than is the case in a lot of places. So that inter-annual variability is intrinsically very high. And even within the winter wet season, you get dry spells and wet spells that make it feel, you know, sometimes it can feel like summer in January, and sometimes it feels like January in January. And it is that intrinsic variability, and the physical and climatological reasons that underpin it, that make it so that California's climate is probably going to become even more variable as things get warmer, especially when it comes to precipitation. So we actually don't necessarily expect to see more variability in temperature, it's going to get warmer, and the range and temperature might actually decrease as it gets warmer. 

When it comes to precipitation, the story is really very different. And in California, at least right now, the best evidence does not suggest that we're likely to see huge changes in overall average precipitation, there's a little bit of uncertainty whether it gets drier or wetter on average. Currently, the best evidence leans towards slightly wetter on average. But I think that misses most of what's really going on. Because if you only look at the average, you might not quite understand that the same models that project relatively small changes in mean precipitation also suggest a very large increase in very wet events, and also an increase in very dry events. 

So what you get is a broadening of that precipitation distribution, wetter wets, drier dries and wider swings in between the two, all superimposed on top of temperatures that are warmer all the time, which leads to more evaporation and an even greater contrast when it comes to things like streamflow or hydrology or ecosystem health because of course, the living vegetation mostly knows about the balance between precipitation and evaporation. So both of those terms end up becoming really important. So all that is to say, in a warming climate in California, we're not necessarily going to be drier all the time. In fact, you may see a number of periods where it's actually dramatically wetter than we're used to historically. But we're going to see more variability and wider swings between those extremes.

Sam Sandoval  

And following on that description of what are the potential impacts of climate change in California, Kat, could you also provide some references or description of how will climate change will impact atmospheric rivers?

Kat Gonzales  

Totally. So I think I'm gonna try to focus on California. But yeah, as we were talking before, atmospheric rivers are not only a huge benefit for resources, but they also have this double edged characteristic of being able to enact floods and hazards like mudslides, etc. So if we think about the sort of summer and winter, this wet season, cool season in California, it's all connected, right? We're very concerned about fire in California, wildfires increasing and increasing dryness. With climate change, if the amount of water vapor in the atmosphere increases according to this relationship, or thermodynamic relationship, then in the literature, we're already projecting that atmospheric river moisture transport will increase just because of that one aspect, that thermodynamic aspect. 

That's not even considering where the storm track is going to shift, how large scale variabilities such as El Nino is going to interact with all of these aspects. And in California, we're sort of stuck in between this climate regime. We span so many latitudes too, right? So those are a few of the things we can say for certain that atmospheric rivers are going to do in the future, that they're going to get warmer, and they're going to increase in moisture transport, due to these thermodynamic relations. What's unclear is how much really that matters for the precipitation, because like we were describing earlier, you need both the wind aspect and the moisture aspect to induce precipitation. So projecting how wild our floods are going to be or how low our water supply is going to be is going to be a challenge. 

Sam Sandoval  

Yeah, thanks Kat, and perhaps, I mean for me this is a super useful. Many times I go to have different audiences talked about Water in California 101. And every time I start with an atmospheric river, I've been surprised how many times can I say like, who knows atmospheric river? Now I would say about half to 60% of the people in the audience knows it, and I think for me right now, it's super good to, in this time, get trained by the two of you about it. So atmospheric rivers are rivers in the sky. It can be a 10 times the Mississippi outflow. 

They have different flavors -- wind-dominated and those wind-dominated can be represented as a smaller, narrower, moving fast rivers. We also have the moisture-dominated that can be, the analogy might be a large, wide, slow-moving river bringing all of that water. They have benefits for water supply and mitigating a lot of the needs of water. But also it is a double edged sword. You may have also fire, floods, they may increase in moisture, and they might be warmer, but we're not sure by how much.

Daniel Swain  

Yeah, sounds like a great summary.

Faith Kearns  

All right, so I'm shifting gears again a little bit. We couldn't talk to Daniel without talking about drought...

Daniel Swain  

Not sure if that's a good or a bad thing.

Faith Kearns  

Another term that during the drought -- I remember first hearing this term ridiculously resilient ridge -- which I have to admit I still haven't fully wrapped my mind around despite having typed those words myself many times and so I'm just wondering if you can talk a little bit about that phenomenon and what it means for the lack of precipitation in California.

Daniel Swain  

Sure, yeah. So that was an alliterative term that I originally coined on the Weather West blog right at the start of the last big California drought a few years back -- maybe more than a few years back at this point -- but maybe I'll just work backwards. So essentially, it was a term that was used to describe this really persistent region of atmospheric high pressure that essentially deflected the storm track and prevented California from receiving the precipitation it would normally receive during the winter, over several consecutive years. So ridiculously resilient ridge, the triple R, I'll work backward from ridge. 

A ridge is really just another term for sort of an elongated high pressure system. So a region, not necessarily measured at the surface, but potentially high pressure as measured at some level in the middle of the atmosphere. So just think of ridge equals high pressure, essentially. Resilient, I think that that means it's traditional colloquial meaning, which is just that it's had a great deal of longevity, it seemed to be impervious to disturbance. Every time it seemingly got knocked down, it just came right back again, reappeared in roughly the same spot. And ridiculously, well, you know, that's a very formal scientific term, of course, which we actually did formalized in the form of how many standard deviations. I think once you're out in three, four or five standard deviation territory, I think it's scientifically appropriate to use, you know, ridiculous as a descriptor. Really it was just a very statistically unlikely, unusual, rare event that was persistent and was a high pressure system fundamentally, that's what it was. 

The reason why it matters so much partly relates back to what I mentioned earlier about California's distinct precipitation, seasonality, so it's essentially it's wet in the winter and it's dry in the summer, but only one of those two things is always true. It's always dry in the summer, usually wet in the winter, but it's not always wet in the winter. And that's the problem because we really only have one opportunity every year in California to receive that water, via atmospheric rivers for the most part, that is so important to our water supply for the whole year. And if even for a month or two during that wet season we have a persistent high pressure system that sort of acts as a boulder in the stream and deflects the storms and that storm tracks away from California, we're pretty much out of luck that whole year. So persistent ridging, persistent high pressure, during those critical winter months, can pretty quickly lead to drought because it's very easy to lose the singular opportunity we have in a given year to receive that precipitation. And so if it happens over a couple of consecutive years, then we're an awfully big trouble.

Faith Kearns  

I wanted to ask you both about something that you do quite a bit which is science communication, and you both approach it fairly differently. And so I'm wondering if you could each just kind of talk a little bit about how you think about science communication and what the main issues are that you're working on when you're communicating science.

Kat Gonzales  

Want to go first, Daniel?

Daniel Swain  

Yeah, I can go first. I mean, I think it's an interesting time, well, it's an interesting time to be almost anyone in any context with any identity with any professional or personal background. I think it's these are strange times for everyone to different degrees. But I think from my perspective, as a climate scientist, you think a lot about extremes and sort of what one might call in the business tail events or low probability, high consequence outcomes. I just can't stop thinking about the ongoing pandemic and sort of the lessons that we, well, the lessons that could be learned from it, and that I wish we had really seriously considered before it happened, and applied them not just to climate change, but just sort of extreme events in general and how science can be used as a tool to explore the space of what's possible, in the sense that, you know, we know that some of these things are, it's no mystery to virologists or public health experts that a global pandemic was in the long run inevitable and could occur on relatively short notice and would be really bad when it happened. 

This has, you know, the last three or four months, have played out almost exactly as the fictional science fiction movies about how pandemics played out. I mean, it's remarkable how even Hollywood got the big points correct here. And what's interesting to me on a side note, there's no equivalent movie I feel like for climate change that there was for pandemics or volcanoes or meteor strikes. Which is really interesting because in a lot of ways it's the one that is looming even more than these other things, like we've gotten lucky we haven't had the meteor strike yet. We have the pandemic now. But I mean, it's, I wonder how much of that is a science communication challenge? Because it is, on the one hand, the pandemic, you know, pandemic preparedness was not a global priority until the pandemic hit. And then suddenly, it became a huge priority very quickly because the pandemic moved fast. 

Climate change has been around for a long, long time, we've known about it for decades, we've known about how bad it was likely to get for decades too, constantly learning from these physical scientists since at least the 1970s. And yet, we haven't really had that sort of sustained motivation for action. So for me, the science communication challenge is how do we deal with something that a lot of people interpret as a thing that may or may not exist, but even assuming that it exists, that it's a distant process that's affecting someone else, other people, not me, maybe in the future, not affecting me today or the people I care about today in the present. When the reality is actually very much that it is here today, and it probably is affecting you and other people to varying degrees. It's just harder to recognize than something that's as acute as the pandemic. 

For me, the big question that's on my mind these days is how do you break through that, because it's a slower motion catastrophe, but it is a catastrophe. Because it's not going to go away anytime soon, until we make massive societal, global societal, changes. So for me, you know, and for lots of science communicators out there, it's not enough to know the facts, it's not enough to communicate the facts, but how do you really engage more deeply beyond just regurgitating facts? And so, you know, my approach is sort of an attempt to do to various degrees of success, under various circumstances. And, you know, there are some real great science communicators out there who are sitting incredible examples, I think, these days. But it's hard because it has become, even as the pandemic has become highly politicized, where one's political beliefs strongly predict your views on strongly non-political things like the existence of a viral disease, the existence of the thermodynamics changes in the atmosphere. So I think it's an interesting time to be a climate scientist on top of everything else.

Kat Gonzales  

Yeah, for sure. It's an interesting time to be human. Yeah, I think that is explained, that encapsulated a lot of my thoughts the past few months on disasters and societal change. Me personally, I guess I don't consider myself a science communicator as a calling or as a practice, I'm very, very novice. But in my training, I've really appreciated getting to learn best practices for communicating science, it's always been central to how we do science in our lab. So that's just those techniques of explaining things or creating beautiful graphics, that's my job description, I guess. But we're talking about like, bigger picture things. I guess this is where the past few years of my career have kind of diverged in my thinking. 

I have the hours where I do science, and then I have the hours where I think about what's going to cause the amount of systemic and societal change that we need to be able to survive this catastrophe, for all of us to survive this catastrophe. And for me personally, there's not enough hours in the day to tackle that. As a scientist, there's not enough dispersion I could do that would enact that. So it's just a big question mark. I'm just going to put out that a lot of us are struggling with this. We don't really know the answers. Something I've been wrestling with is if academia is so slow to change, how can we expect a country with multiple millions of people...but we can, so finding those elements of hope and shared values and the path forward essentially is key. But for me, I guess I've spent less time and for those who do this, I admire them, but I've spent less time worrying about how's my science supposed to like get into policy right now, because I am just so worried about all the other things going on. So yeah, again like another all hands on deck thing we need to approach.

Sam Sandoval  

Yeah and I think I’m in the same boat it terms of there are things that can we can control. And some of those is actually these efforts in science communication, and I definitely do want to thank both of you for stepping up. And in that regard, actually, it will be good if you can let us know how can we help your work? How can we support you, what are the things that you want to let know the audience so we can support your work?

Daniel Swain  

For me, it's actually building off of what Kat and you Sam just mentioned, which is that I think one thing has become abundantly clear recently is that everything is connected. You can't address climate change without addressing public health, you can't address public health without addressing racism, none of these things are unconnected from one another. And so they all exist along sort of a continuum of things that are arguably broken and need fixing, and they're all urgent, but they are all happening simultaneously. And we can't ignore any of them, realistically, if we want to make real progress. 

I think having these conversations and making those connections explicitly, I think that's what is sorely needed and would be tremendously helpful. You know, over the next few years, I'm really hoping that there's actually a lot more of those connections made formally in science, and outside of science in the policy world, and it's a big ask, that's a big challenge. Maybe it's an idealistic way of thinking about things. It may be idealistic, but honestly, at this point, I don't really see how we're going to solve any of these things until we really start making these deep connections, sooner rather than later. So I think that having those conversations, talking about these interconnections with people and not treating them as these disparate, completely unrelated topics of interest, but very vitally connected things in global society, I think is probably, for me that's where I'm really hopeful that's a connection that people are making.

Kat Gonzales  

Yeah, totally. Word to that. I've just been telling my friends lately that we have to keep remembering that systemic problems require systemic change, that collective problems, require collective change. So just empowering us and encouraging us to get away from the model of thinking that it's one person who's going to change something, it's one person who's going to fix one thing, we're going to wait for that leader to follow them. We are all leaders, we all should be climate leaders. We all should be racial justice leaders, we all should be in the fight for justice, whatever that intersection is, just get in that fight, you know. Really, we've got to imagine something more collective, or else we'll all just burn out and then the force will also burn out. But it is possible and that is how change happens, right? And so whatever it is, just keep going on that path forward.

Sam Sandoval  

I'm just highlighting what you mentioned, that sometimes it's now not only the multidisciplinary work, but it is also speaking the same language and understanding the different connections among systems and making sure that, yeah, everything is connected, and I mean, each of us has to pull our own weight. And I think that hope and certainty will come through.

Mallika Nocco  

Thank you so much for joining us today. We really appreciate you and this is a fun episode, I learned a lot. We are lucky to have you in our community.

Sam Sandoval  

We would like to thank for all the work that you're doing scientifically, and with the community.

Mallika Nocco  

Thanks for listening and join us next time on Water Talk.