In Bolivia, farmers wait anxiously for rains. Meanwhile, Bolivian consumers buy beef and soy from Brazilian suppliers whose operations are clearing the very Amazonian forests that generate Bolivia's rainfall. The atmospheric connection is real but the economic feedback loop is invisible. If Bolivian businesses and policymakers could see this connection as clearly as they see a map of trade routes, would they make different choices about whom to buy from? Would Brazil negotiate differently if it understood that the forests it's clearing don't just affect its own climate, but control a neighboring country's water supply, a country that happens to supply a significant percentage of Brazil's natural gas?
These are the questions that the work of Patrick Keys, a professor at Boston University, raises. He is taking the work of moisture recycling (aka the small water cycle, aka precipitation recycling) in exciting and pioneering directions. He is making the geographical sinks and sources of rain clearer, and then transforming moisture recycling from atmospheric physics into something socio-politico-economic: maps that show which upwind regions supply a location's rainfall, and frameworks for understanding how economic decisions in those distant regions create invisible dependencies. He's building the conceptual infrastructure for embedding atmospheric connections into the social and economic systems that actually shape land use.
Working with Ruud van der Ent (interviewed here previously), he developed the precipitationshed framework, which maps how much rain falling in a particular location comes from which upwind regions. A city might receive portions of its rainfall from countries A, B, and C, or provinces D, E, and F. By making these connections spatially explicit, the framework transforms vague atmospheric dependencies into actionable geographic information.
This required inventing new vocabulary - terms like precipitationshed and evaporationshed had to be coined to discuss atmospheric source regions, linguistic innovations necessary for thinking clearly about phenomena that previous frameworks couldn’t adequately describe. From their paper, precipitationshed is ‘defined as the upwind atmosphere and surface that contributes evaporation to a specific location’s precipitation (e.g. rainfall). We apply the precipitationshed as a tool for better understanding the vulnerability of rainfall dependent regions (e.g. dryland rainfed agriculture).” [Keys 2012]. The precipitationshed gave moisture recycling the same kind of geographical grounding that watersheds gave to rivers.
Keys then applied this framework to map mega-cities worldwide, identifying which might be most vulnerable to land-use change in their precipitationsheds. His 2018 paper combined precipitationshed boundaries, rates of land-use change in source regions, reliance on terrestrial versus oceanic moisture, and robustness of municipal water infrastructure to create a vulnerability index. It was the beginnings of a translation exercise of sorts: how to convert land and atmospheric physics into the kind of comparative risk analysis that could sit alongside assessments of aging pipes or aquifer depletion in a city planning document.
The mapping of atmospheric vulnerabilities built the platform for his next stage of work. Together with Lan Wang-Erlandsson (also interviewed here previously), Keys pushed the framework into new territory: moisture recycling as an ecosystem service embedded in social and economic systems. Places downwind buy from businesses upwind that affect the land. Economic behavior affects how businesses treat the land, which then affects the rain downwind. It’s a feedback loop where economic behavior is integrated into the hydrometeorological flow.
In their 2017 paper “On the social dynamics of moisture recycling,” they propose a new field: socio-meteorology. And they write: “this paper provides insights for resource managers, particularly land and water managers, who are searching for new leverage points within their dynamic social–ecological systems. Understanding where key feedbacks, bottlenecks, and potential cascades are located within a system can provide managers with better information about the consequences of direct or indirect intervention within their systems.”
Keys and Wang-Erlandsson analyzed three countries with different social-ecological configurations. Mongolia recycles 13% of its own moisture and receives 29% from Russia. Its precipitationshed is geographically vast but socially isolated - the moisture comes from remote Siberian forests and Kazakh steppes with little economic or political connection to Mongolia. Niger generates only 9% of its own rain, depending on moisture from Nigeria, Chad, Sudan, and across the Sahel. Here, multiple neighboring countries with active trade relationships, migration flows, and shared resources all influence each other’s rainfall through land-use change, creating a regionally interconnected system.
Bolivia recycles 18% of its own moisture and receives 28% from Brazil. Brazil’s soy and beef production drives Amazonian deforestation, reducing moisture available to Bolivia. Yet Bolivia supplies a signficant percentage of Brazil’s natural gas imports, creating economic interdependence. Global commodity markets, international conservation programs and distant financial actors all influence land-use decisions in Bolivia’s precipitationshed - what Keys calls a tele-coupled system, where spatially disconnected actors drive local change while experiencing no feedback from the atmospheric consequences.
Through these case studies, Keys and Wang-Erlandsson mapped the complex networks of interactions, categorizing different network topologies as isolated, regional, or tele-coupled, and showing how each creates distinct governance challenges. Their work sits at the intersection of economic geography, which examines how location shapes economics; spatial economics, which studies the role of distance and place in economic systems; and ecological economics, which constrains economic analysis by biophysical realities.
The rain falling on your city isn’t just a weather event. It’s the downstream consequence of land-use decisions made by people you’ve never met, influenced by market forces you don’t control, mediated by institutions that don’t know you exist. And your economic choices -where you buy your food, what you consume - are propagating back through that same system, affecting rainfall patterns elsewhere in ways you can’t see.
Economic activity in one location, such as deforestation for cattle ranching, reduces moisture available to another location through reduced rainfall for agriculture, creating invisible water transfers mediated by the atmosphere rather than by shipping containers. Every economic transaction that changes land use is simultaneously shifting hydrometeorological patterns - a causal chain that conventional economics typically ignores.
Keys describes his vision for a coupled model that could simulate these systems dynamically - tracking not just moisture flows but also economic networks, political institutions, social dynamics, and climate change, all interacting in real time. “If you think it’s actually a social ecological system, some sort of complex adaptive system with feedbacks, then you have to be able to do that,” he explains. “You have to be able to kind of have the other part of that connection. Otherwise, it’s like only it’s like half of a simulator, right?” Building such a model would require bringing together network scientists, economists, political scientists, and climate modelers together to connect the dots.
Here is an abridged, edited version of our interview into the exciting fields of precipitationsheds and the socio-economic-political dimensions of rain
Pat: I’m an assistant professor in the Department of Earth and Environment at Boston University and I have been doing moisture recycling research since 2010. My background is kind of a real mixed bag. I have an undergraduate degree in biology from Willamette University. I have a master’s of science and civil engineering from the University of Washington with a focus on kind of water resources and climate change. Then I started an environmental consulting company called Keys Consulting Incorporated, super creative name, and we focused on climate change, impacts, adaptation, resilience with clients all over the place, with projects all over the world. Then I realized I was still really curious about the world and I had a chance to go back to get my PhD and so I took it and I got my PhD in sustainability science at Stockholm University. I was a research scientist at Colorado State and then I moved into an assistant professor role. Then I recently moved to Boston University. That’s like a real quick snap.
Alpha: Cool. Moisture recycling also goes by other names, precipitation recycling and small water cycle. You want to just say briefly what it is?
Pat: My research is quite a bit broader than moisture recycling but I spend a lot of time in that world. For me, the idea of moisture recycling is just a atmospheric water cycle. It’s thinking about the sources of water on the surface of the earth. That’s evaporation, transpiration. It can be either from an ocean or a land surface. The moisture recycling part is understanding where it arises, where it travels through the atmosphere and then where it falls out later as precipitation of some sort. I know some people define moisture recycling on a much more local scale or a regional scale or only on land or all sorts of things. For me though, I take a pretty broad view and it’s just this idea if you’re tracking and understanding the sources and sinks of atmospheric moisture, you are probably thinking about moisture recycling in my mind.
Alpha: Okay, cool. Did you get first get interested in this when you were doing your PhD at Stockholm?
Pat: I went out to the Stockholm Resilience Center and worked with a whole bunch of different people thinking about surface water. I upgraded a surface watershed model for that fellowship. Right at the very end, Line Gordon and I started talking about this other project idea, which was instigated by a conversation Line had had with a colleague of hers, Huberts Savenije in the Netherlands. Line said, hey, I know this guy and he has a master’s student that had just come out with this really cool paper on moisture recycling.
And so we had this big plan to try and build a research team with me and the Stockholm group and with Hubert Savnije and Ruud van der Ent in the Netherlands. So I’ve known Ruud since 2010. I know you had him on your show.
The first paper we sort of cooked up was this idea of precipitationsheds, essentian analogy to surface watersheds - how can we think about sort of airborne sources of moisture, sources and sinks.
I actually still have a notebook somewhere where at the time Ruud and I were trying to talk about what would be the best name for this sort of unit, names like skyshed and rainshed. The other day I found this notebook and I saw all these names crossed out.
Alpha: That’s cool. I like hearing stories about how words came into being because basically you’re defining a lexicon for a new kind of field. I have heard people talking about the precipitation shed.
Pat: Well honestly its I think the most important thing in looking back at that body of work the idea of this unit. Let’s work with this unit in a spatial sense, because it permits talking more specifically about an area on the surface of the earth that might be connected to some other place downwind.
The purpose was to try and see whether or not that was a reasonable thing to do. Like, and that’s actually what my PhD was really all about was like, how reasonable is this approach? How useful is this idea? That’s what my PhD ended up being on.
Alpha: And the ‘shed’ part is to make you think about the watershed to kind of analogize that idea.
Pat: Sort of that. And also that it’s shedding, it’s shedding moisture.
And so we want to understand what was the kind of upwind area, the upwind catchment, so to speak, that supported precipitation in a particular location. I am interested in are people using the source and sink idea more now? And I think they are.
Alpha: So the precipitationshed tells you the source of where you’re waiting for comes from. There’s also one a word for where it goes
Pat: That is something that Ruud coined in a paper that he wrote, I think in 2013 which was the evaporationshed. So that’s where does a region’s evaporation go?
Let’s take Colorado, for example. So you can think of all the places that contribute moisture to Colorado. So that sort of set if you drew a circle around it, that would be its precipitationshed, the place that supplies Colorado precipitation.
The tricky question is how do you draw a line? Or how do you weigh the importance of regions that are contributing moisture? Because ultimately, a lot of regions could be contributing tiny, small fractions of moisture. So at some point, you want to say, Well, we’re not really talking about those places.
So which places are we talking about? That gets to be pretty tricky. And I think that’s also where this very hydrology oriented subject sort of butts right into sustainability science, which is a very problem oriented thing. We’re talking about land use change, we want to understand the consequences of land use change in this particular place. Well, then maybe whatever lines that you draw in terms of upwind and downwind source and sink regions might have to correspond in some way to that would that would matter to this problem that you’re focusing on.
Alpha: So for Colorado, what would you say the precipitationshed for Colorado and what is the evaporationshed for Colorado?
Pat: My master’s student that just graduated just did that. So, so what her work shows, her name is Katherine Humphries. She just finished her master’s degree at Colorado State. And what she found is that the sources of moisture for Colorado, for Eastern Colorado, and especially the northeastern part of Colorado - lot of it actually comes from kind of regional sources. When I say regional, I mean, within Colorado, and adjacent states, there’s a pretty substantial contribution from the Gulf of Mexico, the Pacific Ocean, also from the Gulf of Baja California, so that body of water. There’s also substantial continental sources as well. And how much? I would actually like cite the paper, but she’s submitting the paper sort of like this week, so I can’t cite it yet.
Alpha: How much does California contribute to Colorado’s rain?
Pat: A little bit, some. And I should say again, this is, I’m really speaking primarily about northeastern Colorado right now. But California would some, if only by virtue of the fact that it’s evaporating and it’s sort of, if the Pacific Ocean is making its way to Colorado, California is sort of in the way. And there was a cool study that was done years ago - they looked at the Colorado River and how the moisture that arises from much of the irrigation and the lower watershed of the Colorado River, which is sort of this mass of canals and irrigation. A lot of that moisture then transports, or some of it, transports back up to the headwaters of the Colorado River. So there’s this circularity in the water cycle for the Colorado River to a certain degree, not completely by any means, but to a certain degree.
Alpha: And what about Utah? Is there a lot of evaporation from Utah that ends up in Colorado
Pat: But Utah is a pretty dry place, as you know. So there’s some evaporation from some of the bodies of water and also from some of the higher altitude mountainous areas with forests and so forth. And that’s true of the entire sort of quote unquote, desert southwest. Is there are still lots of mountains, lots of forests at higher altitudes, and those end up kind of showing up pretty clearly as sources of moisture. They’re not dominant by any means, but they do represent sources of moisture. When tracing moisture cycling remember that for a given location, in Northeastern Colorado, Boston, wherever, Oregon, you could draw a line of where this is the moisture coming from, but all those places are also contributing elsewhere.
So it’s not a one to one relationship. You have some moisture is arising in Boston, and it’s going to travel elsewhere. Some fraction will go to a particular place, and maybe you care about that place, but we can’t forget that it’s also contributing to lots of places. So the diffuse character of this quantity makes it a little bit trickier in some ways than say a watershed where there is a more of a one to one relationship.
There was some fantastic work that really dug into the archetypes of landscapes and how they partition evaporation precipitation and runoff as a way to sort of way to understand that water challenges are going to manifest in wildly different ways depending on the kind of which archetype you’re in. If you are in a system where actually you’re dominated by runoff versus evaporation, you’re going to have a different set of challenges for the most part than a place that’s dominated by evaporation with very little runoff.
There was a really cool paper that was based on CESM isotope-based water tracking, a series of papers, Harrington et al. I want to say, that used the isotope-enabled version of the Community Earth System Model that’s developed primarily out of NCAR and Boulder, the National Center for Atmospheric Research. And this isotope-enabled version allows essentially online water tracking while the model is running. They can sort of track the moisture in different ways. And so there was some cool work that looked at North America and parceled it off into these different segments and looked at sort of the exchange of moisture among those segments, as well as disaggregating it from evaporation, interception, and transpiration to really tease out, well, what flux part of the evaporative flux is actually connected, connecting these two places that are transpiration dominated, which tells you something about the importance of land use.
Alpha: There’s seven states in the US that depend on the Colorado river water for their water.It’s a huge problem because it looks like we’re draining the Colorado River, and there won’t be enough water in two decades or three decades. And it’s, officials are at a loss of what to do. So, my question is like, can we restore some more of the rain in the precipitation shed to kind of increase the Colorado River?
Pat: This is such a tricky question. I would say that that level of intervention would presume a way better understanding of the system than we actually have. And by that, I mean, you know, we’re just starting to, I feel like we’re just starting to get a handle on a sense of the variability, etc., associated with some of these kind of the flows of moisture. Atmospheric rivers as a research topic is not that old. Now, I mean, to some people, you’d be like, oh, it’s been around for decades.
And it’s like, that’s still not that old. And that’s a critical component for understanding the major sort of sources, the major events that inject moisture into parts of the Colorado River basin, if not, you know, parts of basins around the world. And so that’s one part. Another part is the fact that a major part is that we now have a moving target with climate change. So almost all of the phenomena that we’re talking about from an atmospheric science perspective that are going to matter for moisture cycling, changes in humidity, changes in prevailing wind pattern, storm tracks, etc., changes in temperature gradients, the fact that the land is drying out more quickly in the ocean, all this stuff is happening and matters for understanding moisture cycling. And depending on the decisions that society makes around its carbon, we could either be a lot warmer or a little warmer. And I would say we’re just now starting to get good comprehensive studies on climate change, the way that different climate change scenarios will have different types of moisture recycling.
Alpha: You have looked at mega cities and how much they can restore their water systems and rain.
Pat: That was something I did during my PhD. In a paper we tried to figure out, is there a way to talk about, in a way like the way we talk about the vulnerability of municipal water supplies, for these mega cities that could arise from the rate of land use change, the amount of land use change in their sort of upwind source areas and their precipitation sheds.
Some cities are pretty resistant to upwind effects in part because they’re coming from the ocean for the most part. Their sources are coming from the ocean. So like humans can only really affect that through global climate change for the most part.
But some places are intensely reliant on terrestrial sources of moisture wehre those terrestrial sources are experiencing pretty dramatic types of land use change. So there are places on the world that could be ppretty vulnerable. There are mega cities whose domestic water, municipal water supply are pretty exposed to upwind change. If I was in one of those highly vulnerable cities, and I was in charge of water, I would probably say, oh gosh, I should make sure I’m aware of this and thinking about this and maybe do our own studies, right?
Alpha: So this is where the land use in the surrounding area upwind, like if you cut down the trees, will affect the rain in that city downwind.
Pat: The amount of how much it affects, how it affects is all, it’s so variable in the sense that it depends on where you are on the planet. It depends on when you get your precipitation. It depends on what is your municipal water storage system.
So that’s something we actually considered in that mega city paper was on a city by city basis, we sort of looked into, well, how robust is their kind of municipal infrastructure for storing, transporting the water for their city? Is it a run of pipe that they’re just sticking a pipe in the river? And it’s like, if the river’s low, they’re low? Or do they have the good work of reservoirs?
Alpha: So which were the major cities you found that the rain did depend on the surrounding area the most?
Pat: The four cities were Karachi, Shanghai, Wuhan, and ChongQing. And so those four cities stood out as being particularly vulnerable across all of the different metrics.
It’s not a surprise to me in part because there is a lot of land use change across Asia. And part that’s part of the analysis is what’s the rate of land use change in some of these places. On that side of the Eurasian continent, the terrestrial sources are very high.
On governance
The FAO, the UN Food Agricultural Orginizaton has a strong interest in this, they’re producing a report as we speak about the benefits of forests to agriculture, and a chapter on that in that report is looking at the kind of say the climate side and a big part of that is thinking about moisture cycling.
That’s a really good example of a pretty high level governance institution that is interested in this topic. I should mention that the one of the funders for Kat’s (Katherine Humphries) work I mentioned earlier. She had done this moisture cycling analysis for northeastern Colorado, for a very extreme year in 2023 where we had the record breaking precipitation events. And so the Colorado Water Conservation Board, a state level agency wanted to understand more about that that extreme year and partially funded Kat’s thesis. And so one of the deliverables for that thesis was essentially, you know, where did that extreme rain come from. How can we understand that extreme rain in the context of, and it was all rain I should say or it was, you know, rain and hail.
So that’s another example of an institution that I think became aware of the possibility to ask this kind of question, in part because one of the faculty in the Department of Atmospheric Science at Colorado State. His name is Russ Schumacher. He’s also the state climatologist. So he is having very much on the ground discussions with producers or like agricultural producers in Colorado about Colorado’s climate. And he’s engaged with policymakers at the state level, talking about Colorado’s climate, not just climate change but you know climate, you know variability, etc.
Agriculture is a huge part of Colorado’s economy, especially some local economies. And so putting that so this is something that he I think he shared this with that agency and they said, oh wow, should be interesting to understand. So I think you’re right that there’s a certain amount of if you can share this, the fact that there is this kind of scientific possibility to understand this phenomena a little bit more broadly.
Ecosystem service
Alpha: You’ve been doing work to frame vegetation generating rain as an ecosystem service.
Pat: One of the papers in my PhD was asking this question, sort of can we frame moisture cycling as an ecosystem service and if so what does that look like what would that mean how would we do that. And it’s good you mentioned Lan Wang-Erlandsson because as part of her PhD she had developed this evaporation model that simulated evaporation partitioning at the land surface. So evaporation is moisture turning from liquid phase to gas phase, but there’s lots of different ways that can happen. If it water can fall on say a leaf that’s called interception and if it re evaporates from the surface of that leaf that’s been intercepted and then re evaporated. If water falls to the soil and gets taken up by the tissues of the plant and then evaporated up a still motto that’s called transpiration. It functions differently you can sort of so you can simulate that so you can if you have land use data soil data precipitation climate data, etc.
I think it was really useful providing kind of a first order estimate, a conservative estimate for the effect of vegetation on moisture recycling. If you wanted to get more detailed you’d use a dynamic model like an earth system model with different land surfaces. Then you could get at a lot more of the dynamic processes, you know, changes in that diurnal cycle changes in seasonality.
And so another scientist, Becky Chaplin Kramer, who has led a ton of ecosystem service work, she invited me to contribute sort of this data and a little bit more analysis to some work where she was trying to combine multiple index of critical natural assets around the planet with moisture cycling being one of those sort of critical natural assets ecosystem services. And so that idea has gotten a little bit more traction and is still sort of ricocheting around. It’s probably what has motivated the FAO to be more interested.
Social-economics of rain
Alpha: Cool. Yeah, I think ecosystem services framework helps certain organizations, and governmental groups too… And then you and Lan also did some work on social ecological modeling?
Pat: We wanted to try and do this idea of how land use can affect precipitation in a different place, and Lan and I wanted to see if there’s a back loop. Is there anything that connects the place that’s receiving precipitation back to that upwind source region? To really investigate that we wanted to think about sort of social dynamics, economic dynamics, political dynamics. And when you start using that language in the context of an ecosystem service, you bump right into this concept of social ecological systems, SES, which are a way to study coupled human and natural environments. It draws a lot from the complexity science community, thinking about how there are feedbacks that exist within these systems that lead to emergent phenomena, all sorts of stuff. If we think about moisture cycling in the context of a social ecological system, then the moisture cycling side is sort of part of the kind of ecological connection, a main feedback in some ways that ecosystems upwind are connected to the ecosystems downwind via the atmospheric water cycle.
We did a deep dive into a couple of case studies like in Bolivia, Niger and Mongolia.
What we tried to do is we said let’s map the precipitationsheds for these locations. And that gives us the boundary in which to sort of consider the spatial scope of these social connections, economic connections, policy connections. And this was really an exploratory paper in some ways that was an attempt to sort of open up this conversation that was already, there were already other kind of spokes into the conversation, but from different communities. So there’s a couple other communities, one’s called sociohydrology and one’s called hydrosociology (they sound the same, but they’re different).
I’d say there’s still a ton to do there. Lan has a PhD student who’s working on this still that’s really starting to dig into some of these social dynamics. I’ve got a couple of grant proposals that have been submitted to try and dig into this phenomenon more in part because if there are, if some places do have much stronger social kind of back loops to their upwind areas. Those are levers of change, right. So those that those are ways that those places are potentially tied into affecting their own precipitation, albeit through totally different mechanisms, policy mechanisms, economic mechanisms, trade mechanisms. I’m really excited about that work. I think there’s a ton left to do so many questions and almost all of them rely on, aside from funding, but rely on really deep interdisciplinary work to understand those systems, which me sort of waiting into initially is good for generating an initial question or set of questions, but beyond that, you really have to start working with experts in their respective disciplines.
Alpha: Could you give an example what you mean by the social back loop?
Pat: Let’s say there is a patch of land upwind that is a mosaic of forest and range lands and croplands. It evaporates water, which falls down, downwind to a city, let’s say Montevideo, in Uruguay. Well does Uruguay buy product from that area upwind? Is its economy locally dependent in any way on the products generated upwind? Is its economic activity would be promoting or discouraging certain land use decisions which are then affecting it.
Alpha: Oh, wow.
Pat: Trying to disentangle that question is complex. A lot of different ways of thinking about the connectivity. There’s network science from there. There’s economics in there. There’s policy sciences in there. Institutional science is even like history involves. And so that’s why it’s a really it’s not an easy question to ask in some ways.
The biological side is simple by comparison, right? We take this grid-ed climate data. We ask this question. We answer it. We write a paper. But then we want to talk about what are the connections that are poorly documented, which do not fit any sort of grid structure. They don’t follow physical laws. How do we study that question to then connect it back?
A dream scenario would be to build a cool simulator to say this is how we could simulate change in an upwind area and its effects downwind. But if you think it’s actually a social ecological system, some sort of complex adaptive system with feedbacks, then you have to be able to do that. You have to be able to have the other part of that connection. Otherwise, it’s like only it’s like half of a simulator, right? Like you’re only simulating half of the system, not simulating all of the other stuff. And if there are some really important slow or fast feedbacks, reinforcing feedbacks, especially you could get some really surprising outcomes.
Alpha: Yeah, that’s good. So yeah, so it’s kind of cool how you’re bridging the people part with the ecological part. Usually people decide to study one or the other, right?
Economists, they treat nature almost as a separate physical process, but economics really is a subset of nature because people are subset of nature.
Pat: You’re going to need a whole other podcast series for that one.
Alpha: It’s interesting that you’re using a complexity theory lens to write so a system and right and you actually have a fondness for looking at things from a systems perspective, right?
Pat: I don’t do a ton of work through that lens but I think actually most of my work is implicitly through a systems lens.
I got my PhD at the Stockholm Resilience Center resilience. And that institute has a deep connection to something called systems ecology, which really came out of systems thinking complexity, complexity science. And so a lot of my academic training, especially my formative PhD training was infused with that sort of lens that systems thinking lens. I actually taught a class on systems thinking, sort of a one shot systems thinking course at CSU, which was a ton of fun to teach. It was such a cool class to teach really asking questions, asking these undergrads to think deeply about sort of the systems that were embedded in what kinds of leverage points exist, etc. We use a book called thinking and systems that was written by Donella Meadows.
Alpha: In economics you have emergence like the invisible hand. So it’s interesting when you’re trying to tie ecosystems with the sociology and then seeing what emergent things arise, and seeing what complexity arises. You change the rules a little bit and you get really different emergences. Maybe you just change a little bit how the ecosystem connects to the sociology. You get very different behavior, maybe more favorable behavior.
Pat: I think almost all the ingredients are out there scattered or different disciplines. I think a really strong big opportunity is some of the advances in, I would say, like complex network science is probably a really good entry point for starting to wrap our heads around some of the social processes. So you could think about networks, social networks, political networks, economic networks, and from those networks, you can actually distill almost rules or kind of governing principles that make that network work, mathematical rules, I should say. And that’s what would permit you to start to develop something like a simulator is if you had, you could translate what you observe in the data in the networks that you find into something that can be represented in numbers. And that’s how then you can really connect that into some sort of simulation. And so there’s a ton of work on complex networks. I mean, that’s a whole massive field with sub fields. And there’s even been some work on complex networks related to moisture cycling to distill the moisture tracking findings into a complex network and then use that network to then ask and answer questions. And then the people have done similar things for people and it’s really just a matter of like, which networks do we need to develop and understand and sort of glue together to make the sort of representation of something that we can simulate and explore change and. So I mean, it’s not for I don’t think it’s for a lack of data per se. It’s a lack of essentially finding the right people to work together to connect the dots that are already there.
Alpha: Yeah, that’s really interesting. The social system is a network and the moisture recycling is a network. You can think about each tree as a node in the water network where the tree decides whether to transpire water up or not, whether to bring water from the groundwater. Basically you’re moving water between these nodes.
Pat: The other thing that I’m really interested in is exploring how ecosystem stress, say from drought can propagate through moisture recycling to affect other places.
So if you’re in Gabon in in Africa, it gets a lot of moisture from the ocean, but also from East and Central Africa, from Kenya and from the Congo Basin. If you’re in Gabon, your precipitation sensitive to the evaporative stress in East Africa. Are you seeing a signal in your variability or seasonality, the actual magnitude of the amount of water that you’re getting? Are you seeing any sort of signature signal of evaporative stress or changes in evaporative stress as a result of that being transmitted through moisture cycling? And the reason I’m interested in that is in part it’s getting at a different aspect of sort of the kind of the complex and the kind of network connectivity of these ecosystems to one another.
I want to understand the teleconnected aspect over land mediated by the ecosystems in multiple ways. This is motivated in part because then it permits talking about the dependence of one place on the governance of another, where you can say this place is actually dependent in some ways on the way this place over here chooses to govern its land. I’ve done a little bit of work on governance of moisture cycling, and this is another way to sort of continue deepening that work through a slightly different lens, not just saying hey these places exchange moisture with one another which is interesting in itself, but saying this place is actually somewhat dependent or sensitive to exposed to the policy decisions in this place in this specific measurable way.
Alpha: Right, yeah. So the ecological stress in one location affects another location, then you would be interested in perhaps helping that other place have less ecological stress.
Pat: In my opinion it’s honestly a route to cooperation right. It’s also something that would lend itself more to sort of trans boundary connections trans boundary cooperation. It’s rare that you would just have two countries next to each other. Canada and the United States are an exception of two giant countries that are next to each other with few other countries sort of involved in their moisture cycling. Most countries at the total mess. And so as a result you have to think about these sort of like consortiums of countries with transboundary relationships.
Alpha: And this opens the door to bring in negotiation and game theory.
Pat: All sorts of other dimensions for sure.
Tipping points and planetary boundaries
Pat: Tipping points is an idea that’s been around for ages. And that idea has been incorporated into the planetary boundaries framing. The planetary boundaries framing is this suggestion that there are specific thresholds within the Earth system that to cross those thresholds would begin the transition to a new Earth system system.
Alpha: Moisture recycling could play into the planetary boundary.
Pat: In the initial framing of the planetary boundaries it was based on surface water and thresholds in surface water related to environmental flows - the flows that are necessary for the ecosystems in a particular river to be sustained and to last and be resistant to change. That was adjusted in the last decade to include quote unquote green water, to look at the evaporative side, the atmospheric side of water, thinking about all the landscapes that are not really where runoff is pretty marginal and where it’s much more about precipitation and the evaporation and really that exchange. So there is now a green water planetary boundary, essentially that other half of the water cycle dominated by precipitation evaporation versus precipitation runoff. And that green water boundary has attempted to fold moisture recycling. I’m a co-author on a green water planetary boundary paper. I will say that the planetary boundaries are still a really evolving concept and I think even the people that are in on the inside would acknowledge that that, you know, every year, there’s new insight about what the details of this or that planetary boundary are.
Alpha: Did you have any final thing you might want to say?
Pat: I think one thing that has guided my research, for moisture cycling especially but I would say it’s true across the board, and is to find the questions that are really interesting to me personally. And then in some ways chasing them even if some of the people that are around me are less excited. I think if I can leave you with one thing something that would be valuable in my view is if you’re excited about chasing something keep chasing it you know because I think that there’s so many more questions out there than we realize to even that we haven’t even realized we should be asking them. I think we have the sense that we’ve discovered everything right that every rock has been turned over scraped clean that there’s nothing left to do and that’s like hilariously not true. Especially in this thorny challenging area of thinking about the intersection of anything physical natural earth system ecosystem hydrologically related and people we still think that we’ve scraped the rock clean we haven’t.
If you’re interested and curious and excited about something keep chasing it even if you have to put it on like not even the back burner like the warming section of your of your stove top that’s like barely keeping it warm. Don’t lose it, right. I’ve had to do that multiple times in my career where I have to set something aside to work on something else for whatever reason but don’t forget that that’s there because that could be the biggest thing that you contribute to like our understanding of the world.
References
Keys, Patrick W., R. J. Van der Ent, Line J. Gordon, Holger Hoff, R. Nikoli, and H. H. G. Savenije. "Analyzing precipitationsheds to understand the vulnerability of rainfall dependent regions." Biogeosciences 9, no. 2 (2012): 733-746.
Keys, Patrick W., and Lan Wang-Erlandsson. "On the social dynamics of moisture recycling." Earth System Dynamics 9, no. 2 (2018): 829-847.
Keys, Patrick W., E. A. Barnes, R. J. Van Der Ent, and Line J. Gordon. "Variability of moisture recycling using a precipitationshed framework." Hydrology and Earth System Sciences 18, no. 10 (2014): 3937-3950.
Wang-Erlandsson, Lan, Ruud van der Ent, Arie Staal, Miina Porkka, Arne Tobian, Sofie te Wierik, Ingo Fetzer et al. Towards a green water planetary boundary. No. EGU21-13583. Copernicus Meetings, 2021.
