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Posts Tagged: fire regime

A Tale of Two Fires: How Wildfires Can Both Help and Harm Our Water Supply

Reposted from the California Water Blog


Now that summer is over and rain has returned to California, it appears that the dramatic 2017 fire season is finally behind us. The effects of fire season can linger, however, with the possibilities of erosion and polluted runoff from burned areas. Napa County has even issued suggestions for how to protect waterways in burned landscapes.

Not all news is bad when it comes to the interactions between fire and water, however. These two seemingly opposite elements can actually work in tandem under the right circumstances, to the benefit of people as well as the environment.

While the North Bay fires were filling the headlines in October, another fire 200 miles away was quietly entering its third month of burning in the Sierra Nevada wilderness. This other fire, known as the Empire Fire, was ignited by lightning. By allowing this fire to slowly burn, the park service allowed natural processes to remove fuels that could otherwise build up and lead to more dangerous fires in the future.

Smoke from the Empire Fire in Yosemite in early October 2017. (Photo: G. Boisrame)

The Empire fire burned through an area in Yosemite where fires have been allowed to burn for over 40 years, the longest period managed with such a strategy anywhere in California. Research in Yosemite and other areas shows that allowing these wilderness fires to burn can increase the amount of water stored in the soil or flowing downstream. In the winter, forest clearings opened up by fires often store deeper snow that melts later than in densely forested areas, meaning more water is released slowly in the spring and summer rather than all rushing out as floods in the winter.

In March 2016, an area with dense canopy cover has almost no snow (left) while only a few hundred feet away an area with burned trees still has snow (right). These photos are from the Illilouette Creek Basin in Yosemite. (Photo: G. Boisrame)

Fires can also open up meadow areas that have been overgrown by forest. Although wet meadows cover only a small percentage of California's landscape, they provide important benefits to the water supply. Meadows reduce the size of floods by storing water during high runoff periods. They also help to store water for the dry summer months by holding that water like sponges and slowly releasing it.

The biggest news about fire and water, unfortunately, is usually about how burned landscapes contribute to erosion, which then pollutes streams and clogs reservoirs. When fires burn homes, pollution risks can be especially high due to the presence of hazardous chemicals. Fires can also lead to larger floods since there is less vegetation to slow water's path from rainfall to stream runoff.

These negative effects, however, usually happen because a large portion of a watershed has been completely stripped of vegetation, and plants have not been able to re-grow in time to stabilize the soil. These kinds of fires are usually caused by a combination of dense fuels and extreme weather. When fires burn under less extreme conditions (lower fuel loads, high humidity, low temperatures, and/or low wind speeds), they can clear out dead fuels and remove a small number of trees while leaving most large trees intact. After the fire, the remaining trees (as well as new growth of understory plants) often enjoy wetter soils and less competition. This increases the ability of plants to survive drought conditions.

Wildfire has always been a part of California – especially northern California and the Sierra Nevada – for as long as it has had lush vegetation and dry summers. Native Californian plants have adapted to this process. Some species, like redwoods, even depend on fire for regeneration. Native Californian people historically used fire as a tool to promote the growth of desired plants.

In the early 1900s, however, those in charge came to what seemed to be a very logical decision: to protect our homes and forests from fire, we should put out all fires as quickly as possible. Although this policy was initially very successful, a century later we have flammable forests with heavy fuel loads, as well as densely packed trees that send large amounts of water into the air through their leaves rather than allowing it to flow downstream or remain underground to be used during droughts.

Large public land managers such as the National Park Service and U.S. Forest Service have lately been shifting away from the strategy of suppressing every single fire. Instead, lightning-ignited fires that are burning under acceptable conditions (not too windy, not too close to infrastructure, etc.) are allowed to burn and perform their natural functions of clearing fuels and thinning forests to sustainable tree densities. Prescribed fires and mechanical thinning are also used in situations where greater control is required to reduce risk.

Fire damage is seen from the air in the Coffey Park neighborhood on October 11, 2017, in Santa Rosa, California
(Photo: ELIJAH NOUVELAGE/AFP/Getty Images)

In this way, letting some fires burn today can prevent catastrophic fires from burning through dense fuel in the future. Preventing such catastrophic fires removes their threat to the water supply – as well as the potentially devastating human losses, as we saw from the Atlas, Tubbs, Nuns, and other fires this year. Increased streamflow, snowpack, and drought resistance in burned watersheds all add to this increased water security. The water benefits of more natural forests are receiving increased attention lately, with some companies even working to set up markets for downstream water users to pay for upstream forest care.

We cannot prevent all wildfires in California. However, by understanding their role in our natural systems and incorporating them into our land management, we can benefit from them.

Gabrielle Boisramé has a PhD in environmental engineering from U.C. Berkeley, where she studied the effects of wildfire on water balance in the Sierra Nevada with Prof. Sally Thompson. She continued this work as a post-doctoral scholar with Prof. Scott Stephens, also at U.C. Berkeley.

Further reading

Boisramé, Gabrielle, S. Thompson, B. Collins, and S. Stephens.  “Managed wildfire effects on forest resilience and water in the Sierra Nevada.”

Lundquist, J. D., S. E. Dickerson-Lange, J. A. Lutz, and N. C. Cristea. Lower forest density enhances snow retention in regions with warmer winters: A global framework developed from plot-scale observations and modeling.

Neary, D., K. C. Ryan, and L. F. DeBano. Wildland fire in ecosystems: Effects of fire on soil and water.

van Wagtendonk, J. W. The history and evolution of wildland fire use.

Posted on Wednesday, December 6, 2017 at 1:25 PM
  • Author: Gabrielle BoisramĂ©

Fire History is Human History

Reposted with permission from the Fire Adapted Communities Learning Network

I recently found myself venting about the idea of “nature.” The concept has always bothered me. There's an inherent separatism in it—an implicit line in the sand between humans and nature, where we can and should appreciate it, but we think we aren't really part of it.

I struggle with these ideas often in my work. I've had people question the naturalness of frequently burned landscapes if they know that humans had a role in ignitions—even if human ignitions extend thousands of years into the past. The dichotomy runs deep.

So it's always refreshing to see 

Credit: Lenya Quinn-Davidson, Fire Adapted Communities Learning Network

scientific reinforcement of what I know in my heart to be true: people are a part of the landscape—a very powerful part.

This is the theme of a recent paper by Alan Taylor, Valerie Trouet, Carl Skinner and Scott Stephens in the Proceedings of the National Academy of Sciences (PNAS). The paper looks at California's Sierra Nevada over the last 400 years, and it finds that socioecological change—human activity—has been the primary driver of changes in the region's fire regimes, more so even than climate.

The paper, which came out late last year, incorporates a unique blend of fire history and human history. The authors were able to reconstruct a 415-year fire record for the region using a combination of tree ring studies and 20th century data on annual area burned. From there, they calculated a “fire index” for every year since 1600—basically a metric that combines fire occurrence and extent, and tells us how much fire activity was going on during that time. Those indices were used to identify large-scale shifts in regional fire regimes, which the authors compared with patterns of human settlement and management, and with climate.

The authors identified four major fire regime periods since 1600, which they were able to link to patterns of human activity. The first regime shift occurred in 1776, triggering a 90-year period of enhanced fire activity. During that period, the mean fire index was almost twice what it had been before 1775. The paper shows that this regime shift was coincident with the timing of Native American contact with Spanish missionaries in the region, which occurred in 1769. It's not exactly intuitive, but the authors explain that the decimation of Native Americans—and a subsequent reduction in light burning—allowed for an increase in fuel continuity and wildfire activity during that period. This connection is further evidenced by the increased sensitivity of fire activity to climate—a relationship that was relatively weak when Native Americans were conducting widespread burning.

The second regime shift occurred in 1866, at which point fire activity dropped back to pre-1776 levels. The authors attribute this shift to major land use changes across the region—mostly associated with intensive livestock grazing, which denuded herbaceous vegetation and had notable effects on fuel continuity and fire spread. During this period, fire activity was also less sensitive to climate than it had been during the previous period because of a lack of fuels.

Credit: Lenya Quinn-Davidson, Fire Adapted Communities Learning Network. Hayfork, where Lenya grew up, has been an epicenter of fire activity in recent decades. It's also been the focus of fire history studies by Alan Taylor and Carl Skinner, who co-authored this new paper.

Credit: Lenya Quinn-Davidson, Fire Adapted Communities Learning Network. Hayfork, where Lenya grew up, has been an epicenter of fire activity in recent decades. It's also been the focus of fire history studies by Alan Taylor and Carl Skinner, who co-authored this new paper.

The third shift is the one we're all most familiar with: the beginning of the fire suppression era in the early 1900s. During the fire suppression period, in which we're still operating today, fire activity has been 4–8 times less than in any other period in recent history. Likewise, the fire-climate relationship has been weak for most of this period; the 20th century has shown increased warming trends, yet fire activity has largely been squelched by human activity. Only in recent decades have we seen a strengthening of that relationship, as a perfect storm of high fuel accumulations, longer fire seasons and drier conditions enables fires of unprecedented severity and size, appearing to override the moderating effects of human management.

My last statement should give us pause. Are we entering an era—perhaps a new fire regime period—where changes in climate are overwhelming our human capacity to influence our landscape? The work of Westerling and others (check out my first Science Tuesday blog from last February) would indicate that we're headed in that direction.

A graph of the fire history described above

Figure 2 from Taylor et al., 2016: “Regime shifts in time series (1600-2015 CE) of Sierra Nevada fire index, summer moisture (i.e., PDSI), and summer temperature (i.e., WANT). A switch to new regime (fire or climate) is shown by a vertical line … The number of tree-ring sites recording fires in each year for the 1600-1907 CE period shown by a dashed line. The fire regime periods are indicated by color shading: 1600-1775 CE (green), 1776-1865 CE (orange), 1866-1903 CE (blue), and 1904 CE to present (pink).”

But the really valuable thing about this new paper by Taylor et al. is that it gives us a larger context to work within. Yes, recent decades have had increased fire activity and increased sensitivity to climate—we've all seen it. But let's remember that our collective frame of reference is relatively short; for most of us, our vision of what's natural or normal in terms of fire comes from the mid to late 20thcentury—the height of our fire disconnect. This paper allows us to look back and see that the human relationship to fire is enduring and powerful, and that our biggest mistake in the last century has been to deny ourselves that intimacy—to value “nature” over nurture. History tells us that we should be able to buffer climate effects, but only if we actively engage at a grand scale. I think we're ready.


Taylor, A. H., Trouet, V., Skinner, C. N., & Stephens, S. (2016). Socioecological transitions trigger fire regime shifts and modulate fire–climate interactions in the Sierra Nevada, USA, 1600–2015 CE. Proceedings of the National Academy of Sciences, 201609775.

Posted on Tuesday, February 7, 2017 at 9:22 AM
  • Author: Lenya Quinn-Davidson
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