The Future of Water
How climate change is altering water as an ecological system—a system that includes us.
This winter’s explosive rainfall events brought weeks of torrential atmospheric river storms to California, yet many of the state’s reservoirs remained below annual averages. “We are in a flood emergency while we still have an active drought emergency,” Karla Nemeth, director of California’s Department of Water Resources, told the Washington Post in January. “That pretty much says it all about the new normal we have with climate change.”
That new normal is a more intense water cycle, with wetter wet periods and longer, drier droughts. Rausser College of Natural Resources experts point out that the warming climate does not seem to be changing either the average or total amount of precipitation—those levels are remaining relatively consistent. It’s the variability that’s changing.
“Climate change is not just simple warming,” says Dennis Baldocchi, a professor of biometeorology, the study of how climate and weather interact with living organisms—including plants, animals, and people. “It’s the timing of the rains. It’s the amount of warming when it’s warm.” Those changes in variation affect how water comes, goes, and moves through entire ecosystems.
Baldocchi and numerous other scientists in the Department of Environmental Science, Policy, and Management work at the complex nexus of climate change and ecosystems—water, the planet, and people. What are the impacts from this new variability, and how do those effects trickle down to the ecosystems that both generate and depend on the water supply? Their findings are a wake-up call that an intensified water cycle has implications far beyond nasty weather.
California as a laboratory
Baldocchi says California’s baseline—with sustained wet and dry periods—is a good model for understanding these changes. He thinks about the water system like an engineer working the knobs on a sink that can be turned to adjust what comes out of the spigot. “What are the input and output knobs? We have to manage these things very, very well.”
His research in the Sacramento Delta, for example, is helping California manage the system that sends water south to support San Joaquin Valley agriculture, which, he points out, uses 80 percent of the state’s water. It all flows through the Sacramento Delta, which is protected from seawater incursion by what Baldocchi calls “a weak levee system.”
Professor of biometeorology Dennis Baldocchi recommends designing water systems for the driest years then taking advantage of surplus in wetter years.
California’s Department of Water Resources is converting some nearby farmland to wetlands—a project that will help protect the critical Delta system from seawater and also fight climate change by sequestering carbon. But the prolonged drought has threatened the project, which requires infusions of water from the Delta. Without enough water, the fledging wetlands will just evaporate, undoing years of work. “Can we deliver a little less water without reversing the carbon sinks that we formed?” Baldocchi says. He is working with the state to optimize water management for dry years.
Turning the knobs that control water supply and demand has helped Baldocchi measure fluxes in evaporation and understand how different environmental drivers—length of droughts, temperature variations—are causing them to change. “With its wide range of ecosystems and microclimates that experience great seasonal and year-to-year variation in rainfall, California makes a good natural laboratory,” he says. “Understanding how our ecosystems respond can inform us how others around the world may react under changing conditions.”
A core problem, he adds, is that the state’s system was designed based on the wet years. Since droughts are part of our natural climate, he says, “We need to design our water systems for the driest years and then take advantage of the surplus in the wetter years,” especially because climate change will amplify these extremes.
Professor of ecohydrology Paolo D’Odorico says we are more likely good stewards if we see the environmental implications of our consumer decisions.
Irrigation is another knob that can be turned to adjust water use. Paolo D’Odorico, the Thomas J. Graff Professor of Natural Resources, studies how to optimize irrigation across a large scale, to sustainably manage the changing climate’s impacts on agriculture. “By looking at the whole world, we can identify areas where we can expand or reduce irrigation, and calculate how many more people we can feed and how much more food we can produce,” he says.
Counterbalancing water across the whole world is an audacious notion, but D’Odorico’s method is straightforward, modeling global data to measure the key components of water balance—precipitation, runoff in storage, and the amount of water crops or other plants use. He divides the world into tiles or pixels, then calculates how much water the crops use and how much rainwater and irrigation water is available, identifying locations where irrigation could significantly improve yields.
A big caveat, he says, is to integrate an awareness of both social and environmental impacts. Irrigation requires investment, and many parts of the world only have rain-fed agriculture. “We need to make sure that even smallholder and subsistence farmers in developing countries have access to opportunities to adopt sustainable irrigation,” he says. “There need to be ways to finance these solutions for everyone so the benefits are not only for large agribusinesses.”
Natural Systems, Human Values
Agriculture and energy sometimes compete for limited water resources, which complicates the water landscape. In regions where water rights can be traded, farmers can leave their land fallow and sell their water rights to energy companies, which require large amounts to extract fossil fuels. Farmers may also choose to grow biofuel crops like corn and sugarcane. In both cases, the energy sector displaces food production, D’Odorico says.
However, if an energy company doesn’t have enough water, it may reduce energy production, which can have pocketbook consequences for consumers. It’s a deeply monetized system, at least in the U.S., so policies and pricing mechanisms like subsidies and laws can be valuable tools—knobs to adjust—to control or incentivize different types of water use, D’Odorico says.
Globalization further complicates things, he says, disconnecting people from the impacts their choices have on resources and the environment. For example, the U.S. imports a lot of berries from Mexico, but much of that production is done unsustainably. U.S. commodity subsidies present a whole tangle of disconnection issues, where crops grown with local resources and large government subsidies are then shipped to other markets. “We are more likely good stewards of the land...if we see the environmental implications of our consumer decisions,” he says.
It’s important to recognize the cultural lens we impose on these issues, D’Odorcio says. “Do we value a pristine system, biodiversity?” He ticks off more human-centered values: carbon sequestration, food security…. “Even keeping nature for the next generation is still very anthropocentric.”
Professor of plant ecology Laureano Gherardi notes that new climate conditions change the way the water cycles through the watershed.
These may be complex issues, but they are more transparent because they take place above ground. To really understand the breadth of changes the new climate variability is bringing, scientists say, you have to look beneath the surface.
Laureano Gherardi, assistant professor of plant ecology, researches the impacts of climate variability on plants and landscapes across long time periods. He’s studying the ways plant communities shift how their roots grow as a buffer against climate change.
As backyard gardeners know, a light rain will hardly penetrate the soil, often just evaporating, while heavier rains seep deep into a plant’s root system. This is true across different ecosystems, Gherardi says. Very wet conditions, with moisture that reaches deep in the soil, may benefit deep-rooted species like shrubs. That causes changes over time, such as grassland changing to shrubland, which is no longer usable for grazing. In agriculture, the same conditions may result in nutrient leaching, as excess water carries soil nutrients far from root systems. Downstream, that can lead to dead zones, low-oxygen conditions that kill fish and other aquatic organisms.
Adapting to new climate conditions generates inefficiencies and changes the way the water cycles through the watershed. “Large rain events cascade down to all the other processes,” he says—there’s a lot of runoff, and the rivers and streams run higher. “All of these hydrologic variables intensify after rain intensifies.” Droughts have comparable cascading effects, he adds, benefiting drought-adapted species that change the ecosystem services being provided.
Most pressing, he says, is to study the interactions of different elements of global change, including land use and ecosystem management, rather than focusing on impacts from just rainfall or temperature spikes.
Gherardi notes that temperature is naturally correlated to seasons within a narrow, predictable range, whereas “rainfall can go from zero today to 30 millimeters tomorrow, so rainfall is inherently much more variable,” making it harder to measure and predict.
That’s important because a lot of water management is just knowing how much there is. Mountain snow is a critical water storage mechanism for the state; when it melts in spring and summer it provides runoff that feeds into the streams—surface water—and it also recharges groundwater and soil moisture.
Professor of hydrology Manuela Girotto stresses how good data can help water managers understand ecological implications and allocate resources correctly.
Manuela Girotto, an assistant professor of hydrology, is adding precision to water measurements in California. An engineer by training, Girotto uses satellite and remote sensing observations and modeling to measure how much snow is in the complex mountain environment and how it’s changing. “Water managers need good data to allocate resources correctly,” she says, “and to understand ecological implications such as how low-soil moisture will affect fires and plant productivity.”
She’s also working with the Berkeley Artificial Intelligence Research Lab, using AI to aggregate data from multiple sources that provide indirect, narrow observations of snow—for example, thermal observations from space that suggest location, and microwaves that can indicate the depth. Taken together, the data may prove complementary, she says, yielding richer information and new insights.
With warming temperatures, Girotto says, it may not get cold enough at lower elevations to turn rain into snow, and what snowpack there is will melt earlier. She hopes more intense winter storms can cancel out some of the problem, with larger storms accumulating more snow higher up.
Girotto also uses satellite data to measure groundwater, which, she’s found, is in decline. In addition to decreasing and less predictable recharge from snow and rainfall, aquifers are also depleted by pumping for farming and industry. While new laws may help curb this problem, “We need to be smarter about how we use that groundwater resource,” she says.
Water and forests
Because forests are a big part of California’s water-storage infrastructure, forest management is a critical knob in the state’s water management. Scott Stephens, an expert in fire science and the Henry Vaux Distinguished Professor in Forest Policy, says there’s ample evidence that forests can be managed to maximize the amount of snow they store while making them more resilient to climate change.
Professor of wildland fire science Scott Stephens warns that high-severity fires are damaging water storage infrastructure.
“We know that forests can actually help conserve water,” Stephens says. “Research has shown that some forest configurations—more open forests with some small patches with no trees—can conserve more snow and allow more water to get into the ground and, subsequently, into streams.” Conversely, canopy that is too dense catches the snow, he says, where it just dissipates.
The Illilouette Creek Basin of Yosemite National Park, roughly 70 square miles in the Upper Merced watershed, is part of a living laboratory where, since 1972, lightning fires have been monitored carefully, but not suppressed. “Those fires have really sculpted that landscape,” Stephens says. The amount of forest was reduced by 26 percent, he says, killing trees and creating openings where other types of vegetation have come in—meadows, grassland, shrubland. The four- to five-acre gaps in the canopy provide enough open space for snow to reach the ground, but enough surrounding trees to keep the areas cooled and reduce wind, which can blow away surface snow. “It stays there longer, like a mini snowbank that melts into soil, groundwater, and stream water,” Stephens observes. “Since you don’t have as many trees in the area, the amount of water being used by those organisms is less,” he notes.
As a former postdoctoral researcher in the Stephens Lab, Gabrielle Boisramé, PhD ’16 Civil and Environmental Engineering, compared Illilouette to six similar watersheds just outside the natural burn zone. All of them lost significant stream water in the last 50 years, while Illilouette saw a slight increase. “There’s just more water in that system,” Stephens says.
When Dennis Baldocchi isn’t working in wetlands, he studies grasslands and savanna—mixed woodland and grassy areas with open canopies, a lot like the fire-sculpted Illilouette landscape. He’s come to see savanna as providing the equilibrium in California’s ecosystem that makes forests resilient. “Historically, both natural fires and periodic burning by Indigenous people would have kept the landscape open,” Baldocchi says.
When fires are suppressed, the forest just keeps growing, Stephens says, thickening the canopy and creating fuel that, when combined with hotter, more prolonged droughts, sets the stage for megafire events. Megafires create huge, continuous swaths of tree mortality that go on for miles, and also kill off conifer seed banks in their path. “It’s really exterminating forests,” Stephens says.
For water, that means a lot of volatility. These open wounds on the landscape are exposed to sunlight and wind, so the snow melts more quickly or blows away. Those effects cascade through the ecosystem, reducing soil moisture, which makes it harder for trees and plants to recover and can lead to erosion. Stephens points to the huge 2020 North Complex fire, which burned at about 60 percent high severity in the watershed that feeds the critical Lake Oroville reservoir. With no plants and trees as anchors, rains carried soil off the land, down the streams, and into Lake Oroville. “These high-severity fires are damaging the infrastructure of water storage,” Stephens says.
In Illilouette, he says, “None of that is happening. The soil moisture is so much greater, there are openings, and there are areas that have low-density forest and high-density forest. The fire is literally self-regulating.”
Cultivating Cultural Changes
Despite the solid science, there’s cultural resistance to changing the landscape—idyllic notions of pristine landscapes have a firm grip on the culture, and, conversely, many people want to own and develop land as they please. And, Stephens notes, many people have a problem with the uncertainty of letting fires burn; wildfires can be managed, but not precisely.
But he is adamant that management, including mechanical treatments and unsuppressed burns, makes forests resilient to climate change, and—not coincidentally—also makes them the most efficient water storage systems.
There is progress. Stephens cites huge increases in state funding for forest management work along with the Roadmap to a Million Acres, a strategy to treat a million acres a year to reduce fire danger.
“I think more and more emphasis will be placed on water as a feature of these lands that needs to be thought of actively,” he says. “It’s got to be about stewardship.” Illilouette, he points out, is just being stewarded by lightning. “Actions can be the absence of meddling.”
Indigenous speakers from the Amah Mutsun Tribal Band and North Fork Mono Tribe speak about traditional forest management practices each semester in Stephens’ classes. “They all talk about active stewardship of land to meet the objectives of the people and the land,” Stephens says—as both a strategy and philosophy that was practiced for thousands of years.
“It feels like we’re headed right back to that,” he says. “I hope we head there quickly, because it’s just so necessary.”