Lan Wang-Erlandsson is a researcher studying moisture recycling. She focuses on the large-scale interactions between land, water, and climate, and their implications for social-ecological and Earth system resilience. She has conducted work on the planetary boundaries of green water, where green water is defined as water that vegetation uses, or more formally as ‘freshwater from precipitation that is stored in the soil and used by plants through transpiration’. She helped society understand moisture recycling as an ecosystem service, and collaborated with the FAO (Food and Agriculture Organization of the United Nations) on reports examining how moisture recycling intersects with the future of agriculture.
Her work has emerged from two scientific lineages. Science often evolves through such lineages. Hubert Savenije was working in the Sahel region of Africa when he wondered why rainfall did not keep decreasing further inland, as it should if the air rained out water closer to the coast. He concluded that there had to be moisture recycling, where moisture evaporated back into the air and then fell again as rain. (Other lineages have called this moisture recycling phenomenon by the names precipitation recycling, or the small water cycle.)
Two decades later, Ruud van der Ent (who appeared here on the Climate Water Project podcast), a graduate student of Savenije’s, built on his work to create a map of global moisture recycling. Lan Wang-Erlandsson would eventually collaborate with van der Ent, as would Patrick Keys, who would work on hydrosocial aspects of moisture recycling (he will appear in a future podcast).
Lan Wang-Erlandsson completed her graduate work at the Stockholm Resilience Centre, which brought its own scientific lineage. The Stockholm Resilience Centre (SRC) was founded in 2007 by Johan Rockström and Carl Folke as part of Stockholm University. Its intellectual roots reach back over half a century, drawing on ecological economics, systems thinking, resilience science, Earth system science, and work on sustainability, tipping points, and the interplay between society, economy, and the biosphere.
From this foundation, the planetary boundaries framework emerged. In 2009, Johan Rockström, then director of the Stockholm Resilience Centre, led a group of 28 scientists to formulate the concept of planetary boundaries in the paper “A Safe Operating Space for Humanity.” The idea was to identify critical Earth-system processes (such as climate change, biodiversity loss, nutrient cycles, land-use change, and freshwater use) that regulate the stability and resilience of the planet, and to estimate thresholds or “boundaries” for those systems that should not be crossed if humanity is to avoid large-scale, abrupt, or irreversible environmental changes.
Here’s an abridged, lightly edited version of our interview:
Lan: I’m a researcher and team leader of the Anthropocene Dynamics theme at the Stockholm Resilience Center.
Alpha: And when you say Anthropocene, that is the era where people are affecting the Earth. You’re studying how people are affecting the water, and how that then affects the whole Earth.
Lan: Yes, exactly. You know, the human impact on the water cycle is really very severe and widespread now.
You could say that in the past 12,000 years during the Holocene, it’s the only time in history that we know for sure that has supported modern civilization and agriculture the way as we know it, right? The Earth system has several tipping points. So the transition could be non-linear. And so whether we exit this, what we call the safe operating space, of the Holocene-like conditions, if we depart from these conditions, it could be in an abrupt way, or it could be in a more gradual way. The boundaries are a set of guardrails. So you could imagine that you’re standing at the cliff, you don’t want to stand precisely at the cliff, but a few meters away, right? So the boundaries are the guardrails. So now we are somewhere between the guardrails and the cliff, and it’s an uncomfortable zone we want to get out of.
Alpha: And then one of the nine planetary boundaries is the water, right? And so that’s what your working on.
Lan: Yes, so the planetary boundaries identify nine Earth system processes or components that are vital for the system resilience to function, for the Holocene-like conditions to continue, to support humanity. Freshwater is one of them. And of course, you could say that some other boundaries also relate very much to water, such as biogeochemical flow that deals with phosphorus and nitrogen pollution, for example. And eutrophication is a big problem. You have the novel entities about chemical pollution, and you know, microplastics in river systems is a big issue. And then the same goes with land system change, biosphere integrity, that also includes life in aquatic systems. We know are much threatened. And then climate change, obviously, that is the main culprit behind the water extremes that we see. So they’re very much interconnected, I would say. But yes, my work so far focused on the freshwater change boundary that was previously called freshwater use.
Alpha: How did you get into the whole water field?
Lan: I’ve always been interested in environmental issues. I remember when I came to Sweden, it’s like 1990. It was a huge transition. So at the time in China, the water, the environment was very polluted. And the only place that was green, I grew up in the city of Guiyang, the only place that was green was the park. So when I came to Sweden, I realized everything is so green, like the whole country is a park. So I think that’s sort of where it started. Oh, you can have it this clean. Is that possible? So I think that ignited my interest for environmental issues.
So it wasn’t necessarily water, but I was very interested in sustainability, sort of how we can make the environment more livable. And also just seeing that it is possible. But then the more I thought about it, I find myself kind of obsessed with the thought somehow that we live on this unique planet Earth in this universe. And we are kind of the only conscious ensemble of molecules and atoms. And that somehow it comes somehow with a responsibility or like just so precious that we live, right? And water somehow is tied to everything that is alive. It was the basic element that made life possible. If you go on Mars looking for life, you would look for water. And water is connected to climate, it’s connected to pollution. It’s very much connected to everything on Earth. So it suited me well to work with water as a person who is very interested in our living conditions as a whole.
My master’s was in civil engineering. Then I did my PhD with water in Delft University with Hubert Savenije and Ruud van der Ent.
Alpha: So you and Ruud were together in graduate school?
Lan: Yes, and Patrick Keys. So we were kind of a trio working very closely together on moisture recycling-related issues.
Alpha: What was the issue that you worked on?
Lan: The aim of my PhD was to figure out sort of how land is quantified, how land-use change affects rainfall. So Ruud has a really cool model that could track moisture, but it didn’t necessarily tell us a story of how land-use change affected rainfall. So my PhD started a couple of years after his. And so the question then was what does this mean in the time when humans, if we look at historically, humans have affected, well, affected basically all land systems on Earth, but transformed around half of the land surfaces, turned it into pasture or agricultural land and with massive irrigation. So how does that change this water cycle? This was my thing I was dealing with.
Alpha: And were you looking at for that social-ecological as opposed to the purely ecological aspects, or you were looking at both?
Lan: Yes, I guess when I started, it was very biophysical in the sense of just looking at the quantitative water flows. And of course, conceptually, Pat and I, we worked a little bit more into sort of conceptual thinking, how can we conceptualize this as a social-ecological system because you can imagine that you might have some sociological feedback that we ever say we haven’t really tested out quantitatively, but you can imagine that, you know, if you deforest Amazon, you reduce evapotranspiration, the moisture input to the atmosphere, decreases the moisture transport in the atmosphere and decreases rainfall. That part we know from the modeling. And so that decreases again, the rainfall not only over the forest itself, but also over the cropland that in the first place caused the deforestation. And the question is how do the people then on the ground want to manage land given the feedback loop or and/or given the knowledge that this is happening? Right. So will they try to reduce deforestation and restore the moisture flow? Or will they sort of have less water and the crop yields are negatively impacted. We should deforest more to have more land, right? So there are sociological interactions and feedback that, that should come out of this, but it’s more like a question mark, I think, than precise answers to that. I have a PhD student now looking into that, but she’s focusing more in the African continent.
The Congo rainforest is actually a very important moisture recycling region. So if you look at the Amazon internally, the moisture recycling ratio annually is around 25, 30, that’s on different estimates. And for Congo, it’s almost a double. But the Congo region is also more interesting because it’s also precisely where the Intertropical Convergence Zone moves around. So you would say that from different seasons, the moisture contribution either goes from the Congo towards the north or to the south. So there are different countries benefitting in different times over the year, very different, yeah, seasonality.
Alpha: Which are the main countries that benefit from the Congo rainforest rain, or getting rain from the Congo rainforest?
Lan: That’s a good question. The three recipient countries that receive most precipitation from the Congo forest are Congo, Gabon, and Equatorial Guinea on a mean annual basis. They receive around 30% of the precipitation from Congo, and during the dry season, so June, July, August, Congo and Gabon receive 50% of the precipitation from the Congo forest. So it’s really substantial.
Alpha: So you’re framing this as an ecosystem service, right? So land use is providing rain?
Lan: Yes. So that was together with Patrick Keys. And so as I mentioned before, even if you just look at the moisture, like the moisture flows themselves, it doesn’t mean that the entire flow is there because of the vegetation. Even if you remove the vegetation, some evaporation will happen. And the other thing is that it depends on which type of vegetation you have. So if you have a forest with a very deep root, they will be able to provide moisture also during the dry season and dry spells. So there’s a seasonality to it as well. But you would see that like the short vegetation like grassland, they wouldn’t transpire as much or at all in the dry seasons. So in that way, you can regard it as an ecosystem service that certain types of especially wooded vegetation are providing to support rainfall. And of course, in the ecosystem service framework, you’ve been talking about regulating services and support. So conceptually, it’s kind of there. But I think what we did together with the co-author leading that work, what we did there was to quantify it. It’s a first attempt to quantify how much of the, if you would have two scenarios, one with vegetation as we have today and one without like barren land, what would the difference be? And that difference we termed ecosystem service.
It’s a simplification, of course, because we know that when you remove vegetation, more things will happen than just that the evaporation will not be there. You will change the wind, you will change the temperature. So a lot more things are going on. But yes, from a water balance perspective, you could call that quantification the ecosystem service of the moisture-supplying service from vegetation. And of course, you can combine it with other system models, runs and all that, compare the difference between barren and vegetated land.
Alpha: Okay, cool. And so did you look at other places apart from the Amazon and the Congo rainforests, other continents like the ecosystem services providing rain for? Like have you also studied by like, say, in Europe, how land use is providing ecosystem service of rain?
Lan: Yes. So one thing with the ecosystem services, it’s not just the amount over the year, but it’s also sort of when you want to look at the ecosystem properly, you actually also need to look at in what way it’s resulting in actual benefits. Right. So actually, you might want to know to what extent is it mitigating droughts or heat waves in the downwind area. And so we had a paper with Agnes Pranindita who looked at it. And so in her paper, she analyzed heat waves in Europe and found that forests tended to have a disproportionate influence on moisture supply during those times, which is very aligned with our understanding of how forests operate that they are able to be this buffer, they can store the water and then release it also when it’s dry, which helps mitigate not only locally, we know that from previous studies that forests have this cooling effect locally, but also remotely by providing moisture.
Alpha: So how does this all connect? So you’ve been doing work on this tipping point, right, on all the planetary boundaries? So how does the ecosystem services of the atmospheric water play into the planetary boundary?
Lan: So there are several parts to this. If you look at the planetary boundaries in terms of tipping elements, for example, the Amazon forest or the tropical rainforest, they are massive land carbon sinks, right? So they are helping us currently, they are doing this as a service of absorbing CO2 emissions from fossil fuels. And but when they die, they will instead be releasing carbon to the atmosphere. So instead of helping us, they will make our efforts to come down to the 1.5 degrees, Paris Agreement more difficult.
So the moisture cycle of course plays a role in stabilizing those important carbon sinks. There are estimates. If you look at the carbon sink strength of the Amazon, and if you continue to extrapolate that, there are estimates that say that this switch might happen already over the next decade, depending on deforestation rates, not only on moisture recycling, but moisture recycling kind of amplifies that effect, right? So if you cut down the forest, you not only cut down the forest, but also remove the extra moisture supply that comes with the forest. So it certainly plays a huge role there.
And you also have the irrigation effect. You have the massive irrigation in India that is depleting groundwater to start with, but also modifying. So you could say that you have the important monsoons in the Asian continent there that is supporting agriculture. So you have the dry period and then you wait for the monsoon for the crop to grow. So it’s very important. But there are also research that has shown that if you pump that much water into the atmosphere, by irrigating the crop lands, you are decreasing the temperature over land, right? So there is then less difference between the land and ocean temperature. So the monsoon is drawn into the land because of the temperature gradient, but it’s warmer over land and cooler over ocean. And the warm air over land is rising and therefore sort of driving the monsoon into the Asian continent. But if you reduce the temperature gradient, you might have an effect on the monsoon. So some research has pointed out that it’s actually delaying the monsoon onset, for example, which is a continental to planetary scale change.
These are two examples where this kind of land-atmosphere interaction come into the planetary boundaries framework. And of course, the planetary boundary framework, the way we represent it, we only looked at the percentage of land areas that experience a departure in either stream flow or soil moisture, root-zone soil moisture. So it’s a simplification, but you could say that we looked closely into many, many more. So under the hood, the planetary boundaries conceptually is trying to account for all these things that are happening. And then we provide a simple metric as percentage of land, they’re waiting for those. But the understanding is that all those things are connected.
Alpha: Right. It’s a very complex non-linear process that you’re trying to simplify enough so it’s a useful governance thing. So like in the Amazon, if the forest is providing rain, but that rain is needed to grow the trees to sequester the carbon. And so if there’s that feedback loop that if you get past, you’ve crossed the rain cycle, you’ve crossed the carbon sequestration, and then it has all these ripple effects throughout the whole. And the whole Indian continent, if you shift the temperature gradient by what are we doing with the water, then that shifts the whole way that rain cycle gets driven.
Lan: Yeah, so these are large-scale processes. And we don’t know all the answers. And there’s quite some uncertainty, which is partly where the planetary boundaries are coming to also just not knowing the large risk or risk in itself.
Alpha: And then you also, in this whole planetary boundary framework, you’re looking at green water, right? Can you explain the green water framework for water?
Lan: Professor Malin Falkenmark was the one who coined, or colored the water cycle. So she termed the blue water and green water decades ago in an effort to help policy makers to understand the issues particularly related to green water. Because I think maybe still, but particularly decades ago, a lot of the focus on water resources management was on so-called blue water. So the liquid water, visible water in rivers, lakes, and groundwater and much less attention is put into the green water. So the water in soil and that contributes to transpiration. The water that is actually used in most photosynthesis processes by both ecosystem and grown crops.
So her point was like, look, we have blue water resources, everyone seems to understand that. We have infrastructure, all the water resource management is looking into that. But how about green water, which is actually over 80, 90 percent in many places. Thinking in South America, Africa, it is still over 90 percent of the agriculture that relies on green water only. So only rain-fed, using very little, our known irrigation water, right? So, yeah, so that’s the difference between green and blue water. So this was actually originally coming from there. And before I worked with the green water of the planetary boundaries framework, the planetary boundary for water was called freshwater use. So also focusing on blue water. The interesting thing is that if you look into the supplementary material of the 2009 paper by Rockström et al., there’s a whole page on green water, on the green water’s role for monsoon system, for Amazon, for tipping elements, for sustainability. So everything is there, but it was under the hood. So somehow it didn’t communicate. And there was lots of misunderstanding on if we just look at freshwater use, how much we use, that it doesn’t really reflect the planetary risk we are facing.
What is the Earth system impact of using, you know, a little bit more water in total over the globe? So different kinds of critique. That was one. In other words, that, well, if you lump it into a volume of water that you can use globally, what happens if you use a lot of water in India and none in Europe or US? Is it still safe or not? And of course, what we see is that water changes. The impact on Earth system are much more widespread. It’s not just about water use. It’s not just about how much water you withdraw from rivers. That matters. And it’s there. It’s all there in the 2009 paper, but they just didn’t come out clearly. And by not presenting it clearly, a lot of those things were sort of lost in the margin. So what we did was to say, you know, we’re not interested in maybe freshwater use per se from an Earth system perspective, but we’re interested in freshwater change. And we want to have a sub-boundary for blue water and a sub-boundary for green water. Yes, it was years of discussions with many colleagues. Yeah, as you can imagine, this kind of work really needs interdisciplinary and collaborative work. It was fun.
Alpha: The freshwater is made up of both blue and green water, right?
Lan: There are two sub-boundaries to the freshwater change boundary now. One on blue water, which is represented by the percentage of land that experiences local deviations from baseline of stream flow, and one for green water that has a similar but measures root-zone soil moisture.
Alpha: Right. And so traditionally hydrology in the 20th century was focused on blue water because that’s aqueducts and piping water and everything. But so now you’re saying, the green water, which is the water that’s accessible through the soil, the plants, is actually really key. And you’re also saying this is through teleconnections, right? Like teleconnections being like the water in one area impacts, you know, somewhere else. Continents, right? Because you have the water being transpired and it affects large-scale atmospheric circulation of water and through the atmosphere.
Lan: Yes. So water is so much more than just river water, right? So it is, yes, it is the transport of nutrients or pollutants. It is the habitat of life or biodiversity and it is climate. It is the cloud. It is the, you know, and the cloud decides how much of the, it regulates how much of the sun’s radiation reaches the Earth. So it is albedo. So, yeah, I started with like water is so much of the identity of the Earth system. It’s a water planet.
Alpha: And the whole atmospheric transport system, we kind of forget about it, right? But like it is actually how water is getting to different places.
So have you been trying to work to try and get this into governance and try to get this into the political system to awareness of the importance of all this atmospheric water transport?
Lan: Well, there are many efforts on that front. And we see a lot of interest from the UN agricultural extension FAO (Food and Agricultural Organization of the United Nations). With David Ellison, Pat Keys, and others, we wrote an article for the FAO journal clearly describing the water cycle, also including the atmospheric one.
And the thing is that when you reach out to policy makers, one thing that is important is also that it’s not that simple. So I think when we have an article showing this is the ecosystem service of the moisture supply of forest. Scientists will understand that this is one of many processes and mechanisms. And when you reach policy makers, you have to sort of put it in the context. It might not be the best idea to plant a monoculture plantation in a dry area, as we know. So context is everything. So it’s very important to, when we reach out to policy makers to do it together with others and both sort of accounting for the multifaceted sort of when is forest benefiting the water cycle as a whole, both allowing local rivers to not dry out, and also, at the same time, promoting biodiversity.
That a monoculture is often not particularly resilient and it’s not just about the amount of water in a particular time, but also how sustainable is it? And especially under climate change, the water cycle is changing. So that’s one of my other research projects where we look at the resilience of forest-based climate mitigation measures. There’s a lot of effort and political will, which is nice, to restore forest systems. But how resilient is it? Where should we do it? And also without harming local communities. Whenever you want to do something on land, there is something on that land already. So it’s not so simple.
Alpha: So the FAO, that’s one of the leading agricultural global entities, right? It’s a big deal that they’re actually recognizing this.
Lan: Yes, I do see that. And also in conferences, more organizations are talking about it. Johan Rockström is the co-chair of the Earth Commission and the Global Commission on the Economics of Water. And they had a couple of reports now quantifying the moisture exchange between countries and frame it in the way that policy makers understand. So if you frame it in terms of the economics of water, if you frame it in terms of a trans-boundary issue. I think it’s really being taken up by people who are understanding it. I’m not sure if it’s been taken up in policy but I see it coming.
Alpha: Okay, so it’s being recognized, but there’s not necessarily policy passed to restore land use to increase the rain.
Lan: Not that I know of. Okay. Not like particular policies. I don’t know if it’s good or bad because, you know, you don’t want it to be misused. I really hope it’s taken up in a good way and used in the right way.
Alpha: In the whole hydrology or climate movement, is it just a very small section of scientists talking with governance people, or is there more. Is it growing?
Lan: Sophie te Wierik’s finished a PhD now a couple of years ago. And so she was really focusing on the governance of atmospheric moisture. She’s at Potsdam Institute. I also just generally see more governance people being interested, which is always good because we can only do as much as with our more biophysical background. We can try to reach out, but ultimately you need to work together with governance scholars. We had a collaboration with a number of people who worked on implementing moisture recycling in life cycle assessment. That was one example of trying to implement it in actual thing that are being used by companies. And we have another project working on the Earth System Impact Score, led by Steve Lade in Australia. Who is trying to create a score of planetary boundaries interactions, and we’re not there yet, but eventually we will hope to integrate moisture recycling considerations also in this metric, which is something that can be used by companies and investors to assess not only their local impact, but the normal metric will do the job for, but also how their operations affect a large-scale kind of planetary scale. And it’s a continent or the planetary scale impact.
Alpha: Do you personally talk to people at FAO?
Lan: I talk to them. We just had put together a a report with FAO together. So I think this organization also is really happy to work together with researchers. And of course, the majority of my time goes to research, but I do try to make a good chunk of time to contribute to reports and policy briefs to the extent that they also reach the policy makers and I think that’s a part of me fearing that our concepts will not be used in the right ways. I can’t keep my fingers away from at least reviewing those reports. Okay, yes, it’s formulated in a nuanced way. But I don’t know if policy makers like that. I think they kind of prefer maybe the simplest straightforward recommendations and here I come with the more nuanced recommendations.
Alpha: Do you have any last words to share?
Lan: I think this field will continue to move forward and hopefully go more interdisciplinary so that it can have a real impact. I think we are starting to recognize and realize that the water cycle is not just a function of the climate, but a part of the living system. So those that live on earth depend on the movement of water. It’s a tiny fraction of earth water that is fresh that is used for all life on land and the reason it can be used is because it’s in movement. So it’s a renewable resource really. And this water cycle is also then dependent on life. So at the same time that the water is giving life, the life is also giving water.
We really need to think of the water as an intertwined thing. The water cycle we have today is not just a biophysical abstract thing, but it’s something that is shaped by the whole evolution of life on earth and a result of co evolution with life. And now we are part of as a species, we are part of shaping the water cycle. And I think we need to be really careful thinking about how we are shaping it, whether it’s in a way that is good for us or in a way that is practically self harm. And we are the only species that is doing this knowingly and consciously. So I think with that lies a big responsibility.
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Lan Wang Erlandsson’s publications and other info on her web page.
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“A planetary boundary for green water.” Wang-Erlandsson, Lan, Arne Tobian, Ruud J. Van der Ent, Ingo Fetzer, Sofie te Wierik, Miina Porkka, Arie Staal et al. Nature Reviews Earth & Environment 3, no. 6 (2022): 380-392
Falkenmark, Malin, Lan Wang-Erlandsson, and Johan Rockström. “Understanding of water resilience in the Anthropocene.” Journal of Hydrology X 2 (2019): 100009.
Wang-Erlandsson, Lan, Wim GM Bastiaanssen, Hongkai Gao, Jonas Jägermeyr, Gabriel B. Senay, Albert IJM Van Dijk, Juan P. Guerschman, Patrick W. Keys, Line J. Gordon, and Hubert HG Savenije. “Global root zone storage capacity from satellite-based evaporation.” Hydrology and Earth System Sciences 20, no. 4 (2016): 1459-1481.
