Drying Landscapes

The gradual drying out of landscapes over time — a process known as “aridification” — is becoming a significant global challenge in the face of a warming climate. Unlike droughts, which are temporary, aridification involves a sustained, long-term shift toward drier conditions. Aridification impacts soil moisture, water availability, agriculture, and ecosystems, and also increases the frequency and severity of wildfires. As more regions experience reduced rainfall and higher temperatures due to climate change, understanding the causes and consequences of aridification is essential for developing strategies to adapt to these shifting environmental conditions.

AGCI recently spoke with Brad Udall, Senior Water and Climate Research Scientist/Scholar at Colorado State University’s Colorado Water Institute, about aridification as a global change issue and the many ways drying landscapes impact communities and ecosystems.

AGCI: What is the phenomenon of drying landscapes and where are they occurring?

Brad Udall:  So drying landscapes are examples of this term that we’ve invented, “aridification,” which means that areas are drying, or aridifying. Not every year is drier, and not every year is warmer, but clearly warming and drying tie directly into this concept of aridification. 

And so how did we get here? We now have an atmosphere that wants to hold more moisture — picture a bigger sponge above your head. We have droughts occurring as they normally would in a pre-global-change world, but these new droughts oftentimes are more intense because of less precipitation, hotter temperatures, and of course, this atmosphere that wants to suck up all available moisture. Plants want to use more water because any given day is likely to be hotter, and we now also have earlier springs and later winters, so there’s a longer growing season. In general, we now experience more evaporation and more transpiration — that is to say, plant water use. 

What’s interesting to me is where this is occurring. We initially used to think just the dry areas are going to get drier, and that’s it. Well, we’re now seeing it’s actually occurring in lots of places — arguably, in more places than not. A good example is the fires in Canada last year. An enormous, unprecedented amount of land there burned, six times what normally burns. At one point in time, they had almost 30 megafires going in Canada. That boreal forest, because of high temperatures and drought, all of a sudden looked like it was aridifying as well.  

Around 2020, Jonathan Overpeck and I wrote a paper in PNAS about aridification in North America in response to an accompanying paper that talked about how the Missouri River basin was drying out. So this is occurring in lots of places, not just deserts. It’s easy to assume that it’s just occurring in the American Southwest and existing deserts around the world, but that’s not true. Arguably, the Northeast U.S. is not suffering through this, but it feels like just about everywhere else is. 

AGCI: And how are drying landscapes a global change issue?

BU: Well, higher temperatures are one area. As the atmosphere warms, it wants to hold more moisture — seven percent per degree Celsius, theoretically. And so it’s this bigger suck or sponge above our heads to absorb moisture. We’re also seeing these unusual storms in places like California. The term that’s been coined is “weather whiplash,” right? You get really big storms and then nothing, really big storms and then nothing, and those nothing times tend to be longer and warmer and drier. And that leads to aridification. Aridification is clearly tied into warmer temperatures, changes in precipitation, and changes in how the atmosphere works — that’s what makes it a global change issue.

AGCI:  How do drying landscapes and aridification impact people’s lives and communities? 

BU: It’s almost easier to say how they don’t impact lives. In these drying landscapes, you have less water, and you have more and bigger fires, right? And while moderate-intensity fires are important for ecosystems, the megafires we are seeing are just unbelievably destructive to ecological and to human systems. 

You know, when I bought my house here in Boulder, [Colorado] in 2003, I never thought I was at risk of having my house burn down. But because of where I live, right on the edge of open space, all of a sudden, this is a real issue. In the 2021 Marshall Fire, which started only two miles from my house, almost 1000 homes burned down. One of those could have easily been mine. 

You also get changes in agricultural production. With less water, Southwestern agriculture is now having to share water with cities, and that means less agricultural production, more fallowing, and ultimately higher prices for food. 

You get, on the human side, more expensive home insurance or even nonexistent home insurance for fires in some places. In California, a lot of people are having to join a very expensive, state-sponsored high risk pool with crummy coverage — or, alternatively, go without. My nephew was looking at something like $25,000 a year for home insurance in Truckee, California.

It also affects recreation. Less water means less water for fishing or boating, and less snow for winter sports. Out here in the West, water-based recreation is a really big deal. In places like the Missouri River, low flows can affect river navigation, which carries all kinds of goods and services. Ecosystem services get impacted negatively, with both wildlife and plants affected. 

Aridification really impacts lives in a lot of different ways, from what we eat and how much food costs to where we live and how we protect our houses to changes in recreation and ecosystems.

–Brad Udall

I was just in northern Arizona traveling, and I noticed this area that had burned. It was a pinyon juniper forest. I’m not an ecologist, but it sure looked to me like the PJ’s were going to be forever extirpated from this landscape; it was going to change to grasslands. So aridification really impacts lives in a lot of different ways, from what we eat and how much food costs to where we live and how we protect our houses to changes in recreation and ecosystems.

AGCI:  How does your work relate to understanding and addressing drying landscapes as a global change issue?

BU: My area of work is water in the American West. Because of this drying, we’re looking at having to completely redo the management rules that operate how the Colorado River delivers water, especially how much and to whom. We’re in the process of upending 150+ years of Western water law to deal with these problems, and it’s going to be painful and expensive. Figuring out exactly how these human social systems now need to change to work in this newly dried environment will take time and money.

Over the last 21 years, I’ve focused on how Western water is being changed by climate change. When I first started working for the NOAA RISA program at the University of Colorado — the NOAA program that tries to connect scientists and decision makers — the first challenge was just getting people to realize that climate change was real and that it was going to affect water supplies in a meaningful way. Maybe seven, ten years into the job, I think, the light went on with water managers that scientists were actually seeing these impacts on the ground, and that they, water managers, better start paying attention to science. 

Over time, my work has changed from trying to say, “Hey, this is a real problem and we need to deal with it,” to doing a lot of science communication about new on-the-ground findings, to trying to describe why it’s occurring and how in the future it might continue to occur, and to what we might need to plan for, including some of the adaptations that might be necessary. Also, I talk about some of the non- or mal-adaptations we might do, because, invariably, people come up with crazy ideas that probably aren’t going to work. My work has really been focused on trying to make water managers, and to a lesser extent, the public, understand exactly what is going on and what solutions might look like. I deal a lot with the press too, because they’re very interested in this issue. 

The other area that I consider really important, but some people might not think is important or part of my job description, is trying to talk about the need to reduce our greenhouse gas emissions. I made a promise to myself about five years ago that I was never going to give a talk about how climate was affecting Western water without talking about the need to actually reduce the root cause of these changes. And so nowadays, I spend about five percent of them talking about what we need to do to stop this, because you can’t just assume we can adapt to it completely. We’ve got to actually stop these changes, the sooner the better.

AGCI:  What do you see as the most important part of your work, and why?

BU: Nowadays, it’s trying to keep water decision makers honest about the future. For sure, I have made progress raising awareness about climate change with water managers and the informed public. It warms my heart when climate change is the first or second word out of water managers’ mouths about the issues in the Colorado River. But the next step is then trying to keep people honest about how we really need to plan for a harsh future. Let’s hope it doesn’t happen, but let’s not be naive about what the future might bring. This perspective is especially important now because in the case of the Colorado River, we’re in the process of  redoing water management rules for the next 20 years and putting them in place by 2026. It’s a terrific opportunity to step back and not do just the easy things, but actually do the hard things because everybody’s at the table, everybody’s attentive, and everybody’s in the game here. Let’s not declare victory too soon and set up some solutions that aren’t going to get us to where we need to go. 

The recent history of this, in the case of the Colorado River Basin, is that really important rules were put in place in 2007. Five years later, we determined they weren’t adequate. And then a six-year process ensued to get additional new rules in place. So it took three years to get the initial rules in place, then another 10 years to get some additional rules in place. It’s really slow and hard work to change the management of water supplies that 40 million people depend upon. And so when you get an opportunity to do it, you need to strike when the iron is hot, as they say.

AGCI: When you say keeping people honest, could you elaborate a little more? 

BU: My focus right now is to try and make sure that we’re planning for future flows that are within the realm of scientifically plausible. Here’s an example. In the 21st century, the Colorado River is down about 20% compared to the 20th-century average. Science tells us it could drop another 20% by mid-century. I can’t put a number on how likely that is. Let’s just say it’s plausible. I think we need rules in place that would handle such an additional reduction in flow in a way that preserves the goals that we hope to achieve, including cities that are livable, rivers that are healthy, and that some nationally important high valued ag production continues to occur in the Colorado River Basin. 

In spite of all we know and all we’ve seen, some people are saying, “Well, let’s only plan for the reduction we’ve had so far. Let’s not talk about what might be plausible by mid-century.” This isn’t everybody, but it’s enough people to cause worry. Unfortunately, I’m seeing some preliminary proposals out there that indicate we just need to plan for what we’ve endured over the last 20 years. So my version of keeping people honest is making sure we plan for a “reasonably plausible” future. Once you start talking about big reductions, like an additional 20%, it’s going to be very painful and really expensive. This pain and expense is why some people want to avoid difficult solutions. But it seems like we should do the necessary planning now while we’ve got the opportunity.

AGCI:  What do you see as some of the biggest challenges with regard to drying landscapes? 

BU: I focus on water. That’s obviously at the top of my list. But if you look at everything we’ve previously talked about, water is just a part of that. I mean, how does agriculture adapt both to higher temperatures and less water and still stay profitable? How do we make sure our cities are still livable, but use less water? In the American West, there is a hopeful story over the last 40 years: water use by cities is down significantly. And not just down per capita. It’s actually down in absolute terms, in many places, despite large population increases. Las Vegas is using 30% less water than they did around 2000 and now has a million more people. And that trend is also true in Los Angeles and Phoenix and Denver. These cities have been proactive about reducing water use using technology, appliance rebates, paying people to remove turf, and removing grass in public spaces that never see a human footprint.

Of all the challenges, fires scare me the most. I think we need to figure out how we can better deal with the increased fire risk. How do you build buildings that are more robust to fire? How do you deal with the interface between buildings and wildfires and wild lands? Should we not build in some places? Is there any way to reduce human-caused fire ignitions, the most common way that fires start? In times of high fire danger is there some better way to fight fires before they get out of control? I think there are good opportunities to do things differently so that we can be more resilient with respect to fires.

AGCI: What do you see as some of the most exciting opportunities to address these challenges that you’ve described?

BU: What’s interesting to me is the old connection between crisis and opportunity. We have now a chance to rethink Western water law, which is entirely inappropriate for the 21st century. It’s based on “first in time, first in right,” the doctrine of prior appropriation. It’s a method that four-year-olds discover anew every day: “It’s mine, I was here first.” But most parents tell their four-year-olds, “Think again, you need to share that resource with your sibling or your friend, you can’t just claim that you’re first and you get all of it.” Unfortunately, that’s the system we have. There’s a vast landscape of very valuable property rights in water based on “first in time, first in right.” Because of the way this system got set up, the most senior users tend to be agriculture — it was initially miners, too, but not so much anymore. Cities are, unfortunately, more often than not, junior users. Our system means that in times of drought, you have absolute winners and absolute losers. In the case of the Colorado River basin, you can’t have 2000 senior farmers be the winners and take all the water, leaving 40 million city dwellers without. You can’t fallow cities. 

We’re struggling with how to adjust these property rights for this 21st century. Some of this struggle is how do you implement the notion of “shared sacrifice”? Under “shared sacrifice,” everyone shares a little bit of pain of water reductions rather than forcing all the pain on junior users. I view this as a really good opportunity, because it allows us to rethink how this system has been put in place and make it more appropriate while also doing the least harm to the people who have a valuable property interest that may be their only retirement fund. Rethinking Western water law is hard, but it’s one of the opportunities, I would say. 

Another opportunity is making cities more livable out here. How do you protect and even expand the important greenery and the shade we have without watering lots of less useful turf? You know, shade in the West is a precious resource. When you look at places like Boulder and Denver before humans settled here, there were no trees. This was just prairie grassland. Nowadays, these trees are critical to making this climate livable. Figuring out how to maintain and expand critical greenery in cities is a very worthy goal. 

AGCI: Why should all people care about drying landscapes, whether or not they live in or near an impacted region? Water is such a salient issue for everyone living in the West, but for people who aren’t right there, how do you get that message across?

BU: I would say, first off, no one gets off scot free from climate change. Almost everyone in the US faces climate change threats. Heat waves, floods, rising sea levels, hurricanes, fires, and yes, aridification from climate change, affect millions of Americans. Learning about how we are all impacted in various ways by climate change is useful, because it drives home the point that we all need to do something about climate change — we are all at risk. And we don’t just need to adapt to it, we actually have to get at the root cause and stop all greenhouse gas emissions as soon as possible. 

Perhaps more to the pocketbook, much of the nation’s winter produce comes out of the Colorado River basin. This produce is grown near the Mexico border in Arizona and California, where they have a 12-month growing season. Those winter crops are really important for everybody in the country. Right now, we’re looking at cutting water supplies to those farmers because we have to. Winter produce tends to be the most valuable crops that the farmers grow, so it’s unlikely that they’re going to disappear. But other crops grown at less profitable times of the year will disappear. We need to make sure these farmers have the wherewithal to stay in business throughout the entire year, not just in that lucrative winter growing season. 

Another reason to care about these drying landscapes is that nearby in Mexico but also elsewhere around the world, many important crops are grown in drying areas via irrigation. These areas tend to be great places to grow crops if you have water, because they’ve got tons of sunshine, and crops obviously love sunshine. But most of these areas are already drying, putting the crops at risk. Irrigated crops in aridifying areas are critically important for humans globally. 

California is another great example. A huge number of the nation’s crops come out of California’s Central Valley. And California is at risk of aridification because of its Mediterranean climate. They get one shot every year to get moisture in their wet winters, because the summers are uniformly dry. California has had really big fire seasons in recent years because of crummy winters, which mean very limited water supplies for summer agriculture. So if you like not just winter produce from the Colorado River Basin, but all American produce, this is an issue that will impact all Americans.

On the mitigation side, I am very worried about our worldwide greenhouse gas emissions trajectory. It continues to go up, despite lots of promises to reduce emissions. We need societies and governments to step up and put in place new rules about carbon emissions. Ultimately, that’s how we will fix this, be it through carrots, like the Inflation Reduction Act with its subsidies and tax credits, or at some point, imposing costs for emitting harmful greenhouse gas pollutants into the atmosphere. This is a problem that cries out for big scale solutions that only governments can impose. Neither carrots nor sticks alone will get the job done; we need both. 

It is also important to realize that individuals are not powerless and individual actions can help drive necessary change. I’ve decided I can’t just sit by. I need to walk my talk. So as of this past January, my house is now all-electric. Over the last five years, we’ve installed three heat pumps that allow us to heat and cool smaller areas. We replaced an old gas water heater with an electric one, and we replaced our gas stove with an induction stove. At our request, our local utility came out and shut off our gas so we now don’t pay a monthly gas connection fee. I also installed an electric monitor that helps me track down wasteful electricity use. And we have a four-kilowatt solar array and a plug-in electric hybrid car that does all of our city miles on electricity. I rest a little easier knowing that I’ve done some meaningful things to reduce my own personal carbon footprint.

Bradley H. Udall is a Senior Water and Climate Research Scientist / Scholar at Colorado State University’s Colorado Water Center. His expertise includes hydrology and related policy issues of the American West, with a focus on the Colorado River. He was a co-author of a 2007 Bureau of Reclamation Environmental Impact Statement on how to incorporate climate change into future Colorado River planning studies, the first such document by Reclamation. He was also a co-author of the 2008 Colorado Water Conservation Board report “Climate Change in Colorado.” 

Brad was a co-author of the 2009 and 2018 National Climate Assessments and a contributing author to the 2014 IPCC 5th Assessment. In 2017, along with Jonathan Overpeck, he wrote: “The 21st Century Colorado River Hot Drought and Implications for the Future” which attributed part of the decline in Colorado River flows to rising temperatures. In 2018, he was a co-author of “On the Causes of the Declining Colorado River Streamflows” with Mu Xiao and Dennis Lettenmaier. With Overpeck in 2020, he wrote “Climate Change and the Aridification of North America.” 

Brad has testified in both the U.S. Senate and U.S. House of Representatives on the impacts of climate change on water resources. He has received the Climate Science Service Award from the California Department of Water Resources for his work in facilitating interactions between water managers and scientists and the Partner in Conservation Award from the Department of Interior. Brad formerly served on the American Water Works Association Research Foundation expert panel on climate change. Brad has an engineering degree from Stanford and an MBA from Colorado State University.

See Brad Udall’s AGCI workshop participation and presentations.