Increasing forest fires pose new problems for the water supply

California’s water supply, already compromised by drought and extreme heat, will face another threat as wildfires continue to burn ever-increasing tracts of forest, new research finds.

In a UCLA-led study published Monday in the journal Proceedings of the National Academy of Sciences, researchers found that increasing wildfire activity is “unbalancing” western U.S. current flow from its historical predictability. In areas where more than a fifth of the forest had burned, electricity flow increased by an average of 30% six years after the fire.

On its surface, increased current flow — the speed at which water is carried by rivers and streams — could be seen as a boon to the drought-stricken region. But too much water poses dangers, including increased erosion, flooding and debris flows.

“Water is a really heavy, destructive thing. So if there’s too much of it, or if we’re surprised by a large amount of water all at once, it’s definitely not a good thing,” said Park Williams, associate professor of geography at UCLA and one of the study’s lead authors.

The results underscore how extreme forest fires can alter long-established water cycles. Now, as the state enters a new era of heat, flames and drought driven by climate change, the conversation about water in the West must increasingly include fire.

“We must adapt quickly as the fires are increasing in size and intensity, despite our best efforts to continue to control them,” Williams said. “We – and our hydrological infrastructure – are not really suited for this.”

The three major water basins of the Sierra Nevada — Sacramento, San Joaquin, and Tulare — “should all be on the verge of having experienced enough wildfires to cause surprisingly high flows by now,” he said.

According to the study, the annual wildfire area in the western United States increased by more than 1,100% from 1984 to 2020, the year of the worst wildfire season in modern California history.

With this explosion in fire activity came a new world of dangers and threats, including the destruction of entire cities with flames and the emergence of new fire behaviors, such as the two fires in 2021 that were the first ever to burn in the Sierra.

But the relationship between wildfire and water is one that is only just beginning to be understood. Much of the state’s infrastructure and water management system was designed around the climate and forests of the previous century and is less adapted to the realities of today.

Now the state’s increasingly large and severe fires are burning through trees, shrubs and canopies, which normally absorb moisture, and allowing more water to run into streams, according to the study.

In addition, severe fires can “bake” the floor, making it more waxy and water-resistant. And with less vegetation to hold topsoil in place, there’s more flooding and erosion — sometimes with disastrous results, like the deadly 2018 Montecito mudslide that killed 23 people.

Runoff, especially after severe fires, is also often accompanied by large sediment loads that can affect water quality, said Bill Short, manager of forest and watershed geology at the California Geological Survey, who was not involved with the study.

After a wildfire, “these watersheds can experience major flooding and other impacts as well [such as] Erosion, debris flows and water quality impacts from sediments and burned components,” said Short.

Aerial view of the burned remains of Paradise, California after the campfire.

Paradise, California in November 2018 after the explosive campfire burned through Butte County.

(Carolyn Cole/Los Angeles Times)

The town of Paradise – which was devastated by the 2018 bonfire – was hit by chemicals and pollutants that leaked into water supplies during and after the wildfire, including ash and charred soil, as well as burned plastic pipes and other synthetic materials.

The effects of increased current flow will also create new challenges beyond the potential for more debris and erosion.

For the state’s water managers, who are tasked with calibrating California’s critical supplies each year, releasing too much water ahead of an expected deluge could backfire, resulting in less than needed during the hot and dry summer will.

On the other hand, not discharging enough water could be similarly catastrophic, as in the 2017 Oroville Dam crisis that left more than 100,000 people fleeing a potential flood of overflowing water.

“Any time we change the timing and rate of runoff from what was historically expected – the consequences of wildfires, dry soils, increased temperatures, etc. – we question water management practices and must adapt,” David Rizzardo , manager of the California division of Water Resources’ hydrology division, said via email.

According to Rizzardo, the impact of the recent so-called megafires on water supplies is still a “relatively new phenomenon” that forecasters are working to decipher and account for.

“Fires don’t burn evenly, so their effects vary widely within a watershed,” he said. “It’s quite complex and it will take time to understand and learn from the experts.”

Jeffrey Mount, a water scientist at the Public Policy Institute of California, said there’s still no definitive strategy for dealing with the impact of fires on water supplies because “we don’t really understand it very well.”

“You see spectacular flooding after fires,” said Mount, who was not involved with the study. “Yes, you might get more water, but you also get it when you don’t want it, get more than you want, and it could come with a lot of sediment and debris that creates new management headaches.”

One of the most pressing questions has to do with the scale of the problem.

If a small watershed burns and increases runoff by 30%, that’s a reasonable number, Mount said, but that’s not necessarily what’s happening. According to the California Department of Forestry and Fire Protection, the five largest wildfires in California have all burned in the past five years.

Maureen Kissick, sitting in the rubble of her home, searches through the remains of her china.

Maureen Kissick, seated in her dining room, looks through the remains of her Noritake Tahoe china following the Carr fire in Redding, California August 4, 2018.

(Gary Coronado/Los Angeles Times)

And in some areas well over a fifth of their acreage is burned. Since 2018, more than 54% of the Feather River watershed has been burned in blazes like the Dixie Fire, North Complex Fire and Campfire, said Drew Coe, director of Cal Fire’s watershed conservation program.

Although the researchers primarily used stream flow data from smaller basins in the western United States, the results suggest that burned areas will soon become large enough to affect river flow on a much larger scale.

Williams, the study’s author, said wildfires are now getting so big that “we think it should actually make a difference in the water balance of entire regions.”

The study found a decrease in runoff about six years after the fire, although Williams said more research will be needed to examine the longer-term effects.

Today’s fires are also burning with extreme intensity as dense, dry vegetation has accumulated in the state’s forests.

Some experts said the conditions will create challenges for river and forest ecosystems, many of which are becoming hotter and drier.

“With the warming climate, these forested areas are on a precipice,” Coe said. “And a major megafire coupled with drought can force it into an entirely different vegetation type, and each of those vegetation types has a different distinctive hydrological regime associated with it.”

Jay Lund, co-director of the Center for Watershed Sciences at UC Davis, agreed.

“We’re going to have some really big difficulties running these systems to support native ecosystems, forest ecosystems and aquatic ecosystems,” Lund said, noting that invasive species that are better adapted to heat, fire and drought conditions are replacing the natives could.

But the potential water rush isn’t all bad — and neither is more fire, the experts said.

California evolved with wildfire and in many ways has adapted to its rhythms. Forest management tools such as mandated burning could be a key piece of the puzzle, as fires in forests treated with mandated burning and other thinning practices were more likely to burn with lower intensity and have less damaging impacts on watercourses, several experts said.

Short, of the California Geological Survey, said readiness will also help.

“Under this new and evolving climate regime, we’re seeing these megafires and the number of fires increasing,” he said. “Water managers and water utilities should evaluate their own treatment systems and assess whether they can effectively treat water that has been affected by these fires — whether it’s sediment or the byproducts of ash or burned homes.”

While the notion of increased current flow could be seen as a welcome anomaly for the arid West, Williams cautioned that it’s very rare that there’s “just enough.”

“Usually the case isn’t enough or too much at once,” he said. Increasing forest fires pose new problems for the water supply

Tom Vazquez

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