Wildfires and Water in California
California Department of Water Resources
Why is there so much concern about wildfire impacts? Wildfires have always been part of California’s forest cycles, haven’t they?
It’s true that wildfires are nothing new in California’s forests. Indeed, the state’s wildlands are characterized by “fire adapted” ecologies.[1] Historically, wildfires were essential for western forest health: they consumed dead trees, fallen branches, brush and small, tightly spaced saplings, transforming them into nutrient-rich ash while simultaneously “releasing” larger trees to grow to maturity; they killed insect pests; and ultimately, they reduced heavy fuel loads, ensuring future fires would be meandering, low-level and harmless to larger trees.
Wildfires, in short, are not our current problem. Regular “megafires” are the issue.
What’s the definition of a megafire?
There is some dispute about the term among wildfire researchers,[2] given there can be disparity between wildfire size and impacts. But there is no doubt wildfires are getting bigger and burning hotter and faster; “megafire” is a convenient shorthand reference. In wildfire fighting circles, a megafire typically is defined as any fire that exceeds 25,000 acres in size.[3] Along with size, they’re also characterized by their speed, unpredictably, and potential threat to life and property.
What’s amplifying the increase in megafires?
Climate change is the clear driver of the phenomenon. Global warming is increasing both the frequency and severity of droughts,[4] a trend particularly evident in California over the past 20 years. Droughts stress and desiccate vegetation on a landscape scale, creating vast reservoirs of kindling-like fuel that ignite easily. According to the World Resources Institute, the global area burned by wildfire increased 5.4% per year from 2001 to 2023. Fires now destroy 1.5 million acres more woodland annually than they did in 2001 – an area equivalent in size to Croatia.[5]
What are the risks of megafires, including risks to water supplies?
Megafire threats to human life and property are abundantly clear, particularly in California. A series of gigantic wildfires – including the 2017 Tubbs Fire in Sonoma County and the 2018 Camp Fire in Butte County – killed hundreds of people and destroyed thousands of homes. Additionally, the massive volumes of smoke from megafires pose a profound and growing health threat to Californians.[6] Over the past few years, smoke from large fires have blanketed the state for months on end, aggravating pulmonary conditions and spiking the risk for cancers, strokes and heart disease for millions of Californians.
Serious research into the impacts of megafires on water supplies and fisheries is underway, and the initial findings are alarming.
About 80 percent of the water in the U.S. originates on forested land. In the southwestern portion of the U.S. that includes California, more than 12 million acres of forest have burned in the last 30 years. By stripping watersheds of vegetation, large wildfires increase both flooding and erosion, and thus can impair water supplies. Forested watersheds act as sponges, soaking up both rainwater and melting snowpack for later release. When forest cover is burned to mineral soil, the water can no longer recharge aquifers because it runs off rapidly.[7] [8] Additionally, this run-off is difficult to retain because reservoirs must release much of it to avoid downstream flooding. Such flows also move massive quantities of sediment, polluting streams with soil, ash and contaminants, presenting serious water-quality issues for dependent municipalities[9] and reducing reservoir holding capacity.[10]
Does the increasing incidence of large wildfires pose an increasing threat to salmon and other native fish?
Absolutely. Salmon need cool, clean rivers to reproduce. Intense wildfires immolate the riparian cover that moderates water temperatures, while sediment and ash from run-off degrades water quality and destroys spawning redds. The dire effects of wildfires have cascaded rapidly over the past few years, and now threaten the survival of California’s most endangered salmon populations – the Sacramento River spring-run and winter-run Chinook.[11]
Why should people care about the state’s salmon runs?
Like water, salmon are a public trust resource; the State is legally obliged to protect them. Salmon were once a major commercial and sport industry in California, generating robust revenues and supporting thousands of jobs.[12] While their populations – and the businesses that they supported – can be restored to a significant degree, it is the responsibility of the State to take the necessary steps for their recovery.
Given that California’s megafires are driven by climate change, is there really anything effective people can do to mitigate their impacts on water and fisheries?
Yes. The solutions are relatively simple and straightforward – but they do require public will and adequate funding. To control wildfire intensity, we must reduce fuels in our wildlands. Prior to Euro-American settlement, California’s forests were characterized by large, mature well-spaced trees. When fires did ignite, they were low-level and meandering, seldom reaching disastrous proportions. This was often due to indigenous people burning the forests regularly to accommodate easy passage and encourage the growth of favored food plants.[13]
But decades of aggressive fire control and wholesale clear-cut logging have resulted in forests characterized by smaller, highly flammable trees and abundant woody litter. To prevent catastrophic fire, then, we must reintroduce fire on a broad scale to our forest management practices. By regularly decreasing fuel loads through fire and other means such as manual thinning and livestock grazing, we can greatly reduce the megafire threat to our woodlands, homes, water supplies and fisheries.[14]
[1] https://wildlife.ca.gov/Science-Institute/Wildfire-Impacts#:~:text=Fire%20Ecology&text=Almost%20all%20of%20California's%20diverse,have%20evolved%20to%20survive%20wildfire.
[2] https://nwfirescience.org/biblio/megafire-ambiguous-and-emotive-term-best-avoided-science
[3] https://nwfsc.forestry.oregonstate.edu/biblio/what-do-you-mean-megafire
[4] https://wildlife.ca.gov/Science-Institute/Wildfire-Impacts#:~:text=Fire%20Ecology&text=Almost%20all%20of%20California's%20diverse,have%20evolved%20to%20survive%20wildfire.
[5]https://www.wri.org/insights/global-trends-forest-fires#:~:text=Using%20data%20from%20researchers%20at,all%20tree%20cover%20loss%20globally.
[6] https://ww2.arb.ca.gov/resources/documents/camp-fire-air-quality-data-analysis
[7] https://ca.water.usgs.gov/wildfires/wildfires-water-quality.html
[8] https://labs.waterdata.usgs.gov/visualizations/fire-hydro/index.html#/
[9] Ibid
[10] https://ca.water.usgs.gov/wildfires/wildfires-water-quality.html
[11] https://www.latimes.com/environment/story/2024-08-06/park-fire-threatens-critical-california-salmon-habitat
[12] https://calmatters.org/environment/water/2023/03/california-salmon-fishery-shut-down/
[13] https://www.discovermagazine.com/planet-earth/keepers-of-the-oaks
[14] https://news.berkeley.edu/2023/12/12/twenty-year-study-confirms-california-forests-are-healthier-when-burned-or-thinned/