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Water extinguishes fire, but how does fire affect water? (Part 2 of 2)

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Reading Summary: Water extinguishes fire, but how does fire affect water? (Part 2 of 2)

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  1. The federal data threat angle: The article pointedly warns that state-federal data partnerships are at risk. A blog post could ask: Which specific USGS or NOAA partnerships in California are currently being reduced or defunded, and what data gaps would result for fire-affected watersheds?
  2. Chico flood risk and CalSIP accountability: With Big Chico Creek aimed at a 100,000-person city and a new gage only now being installed, a post could examine how long this data gap existed, what the delay cost in planning capacity, and whether CalSIP is adequately funded to complete its high-priority list.
  3. Compounding fire-flood cycles as the new planning baseline: The dramatic flow reversals documented here suggest pre-fire hydrology is no longer a reliable design standard. A blog could explore whether California’s flood infrastructure, FEMA flood maps, or water rights accounting have been updated to reflect post-fire hydrological shifts in heavily burned watersheds like the Park/Dixie Fire zones.

Full Text

Water extinguishes fire, but how does fire affect water? (Part 2 of 2)

Last week , we introduced our research topic and question (i.e., how does fire impact water?), identified relevant data sources, and determined our pre- and post-fire precipitation events. Following that, we assembled hourly streamflow data from the USGS gages 1 and aligned the flows to the start of each precipitation event for a direct comparison of pre- and post-Park Fire runoff across our watersheds. This week, let’s dive straight into the results (water metaphor!). Figure 1 below shows the hourly precipitation and the streamflow at each gage for each event.

An initial observation is that the rising limb of the hydrograph and peak flow from the pre-fire event occurred more quickly than for the post-fire event (the opposite of what we anticipated). Due to fire burning through vegetation that may otherwise slow runoff, we hypothesized that post-fire runoff would occur more quickly. However, there are some key differences between the precipitation events. One is that the pre-fire event had a higher intensity, so (all else equal) we would expect runoff to occur more quickly. Perhaps the more important difference, though, is of initial conditions. The pre-fire event occurred in February 2019 (a Wet year on the Sacramento Valley Water Year Index ), and conditions in the upper watershed were likely well-saturated, allowing for precipitation to quickly result in runoff. In contrast, the November 2024 post-fire event was the first major precipitation event following several preceding months of dry conditions, so the ground was likely very dry and able to soak up more rainfall before runoff occurred. The same trend of later runoff from the post-fire event is seen across all three watersheds, so factors apart from the Park Fire are likely influencing this.

When we observe the runoff flows themselves, some interesting differences emerge. The post-fire event has two distinct peak flow occurrences. As described above, the first occurs later than the peak flow from the pre-fire event, and the shape of the hydrograph curve differs between Battle Creek (least impacted by the Park Fire) and Deer and Mill Creeks (more severely impacted) 2 . Also, this first peak flow from the post-fire event on Mill Creek (the most severely impacted by the Park Fire) already exceeds the peak flow from the pre-fire event.

The largest and most interesting differences, though, are those associated with the second peak flow, which occurred roughly a day after the first peak flow. Here, the differences between watersheds are most pronounced. The majority of precipitation (3.13” of 4.25” – 74%) occurred during the first 37 hours of the 70 hour event (the pre-fire event lasted 37 hours). However, when the remaining 1.12” (26%) fell, the dry initial conditions were gone, and as another rising limb on the hydrograph took shape, the magnitude of this second peak flow differed widely between watersheds. For Battle Creek (least impacted by Park Fire), the second peak flow was markedly lower than the first (29% lower, relative to the first peak). In contrast, for Deer Creek (partially burned), the second peak was 20% higher than the first, and for Mill Creek (which was nearly 90% burned by the Park and Dixie Fires), the second peak was 66% higher than the first. These flow increases are not insubstantial. The second peak on Deer Creek is more than 1,000 cfs higher than the first peak of the same event and the peak flow from the pre-fire event. On Mill Creek, the second peak flow is more than 7,000 cfs higher than both. For Battle Creek, this second peak was more than 3,000 cfs lower than both.

The timing of these second peak flows also differed between watersheds, with the higher peak flows at Deer and Mill Creek occurring two to three hours before the lower peak flow on Battle Creek. For flood risk, this is a two-punch combo, with peak flows hitting earlier and at higher levels.

Our first conclusion, before we even get to our research question, is that this analysis demonstrates the importance of easy-to-find, accurate, publicly available data about our natural environment. To answer our research question, we needed data to review and analyze, and we were fortunate to find data from multiple state and federal agencies (these are listed in Resources at the end).

These datasets are often developed and maintained through partnerships between locals and larger state or federal agencies. In order to make these data available, folks need to see their value from the local level all the way up to higher government levels. Recent concerns about changes to longstanding state-federal partnerships have shown that the collection and provision of these data are subject to change at any time.

Transitioning to our research question: Before fire, as expected, peak storm runoff flows increased in accordance with watershed size: from Mill Creek to Deer Creek to Battle Creek. After the fire, this was reversed, in accordance with the percentage of the watershed impacted by fire. Battle Creek (largest watershed, least impacted) had the lowest flows, then Deer Creek, and then Mill Creek (smallest watershed, most impacted) had a substantially higher peak flow 3 . This dramatic shift from pre- to post-fire conditions is likely heavily influenced by fire burning vegetation (and litter) that would otherwise slow the movement of water across the landscape and changing soil conditions so that it is not able to absorb as much water (like a sponge). The shift demonstrates the impact that fire can have on water, and this impact consequently has literal ripple effects on everyone and everything downstream.

There is a relatively small human population along Deer, Mill, and Battle Creeks that would be impacted by flooding 4 . However, to close this out, we wanted to briefly circle back to the Big Chico Creek watershed 5 to reflect on the importance of having accurate data about our natural resources. When Big Chico Creek flows out of the hills into the Sacramento Valley, it is pointed directly at the city of Chico, whose population recently crossed 100,000 people . Due to this higher population, flooding from Big Chico Creek has the potential for a much larger overall human impact.

This is where we’d like to end with some good news. In recent years, the State of California has recognized the importance of streamflow data and planned to increase investment in it, as outlined in Senate Bill 19 (SB 19) . The wheels of government often turn slowly, which can be frustrating when problems need to be addressed, but this pace also (ideally, although not always in reality) allows for strategic planning, building consensus, and wise decision-making. SB 19, in turn, has resulted in the California Stream Gage Improvement Program (CalSIP) to install stream gages in locations deemed high-priority and guess what: Big Chico Creek was designated as high-priority, and work is currently underway to install and commission a new stream gage. Woohoo! 😊

Studies have shown that climate change is influencing our natural environment in California with impacts to water , fire , and the people and ecosystems dependent on water and impacted by wildfires. Our analysis demonstrates that water and fire (while opposites) are intimately connected. How we approach and handle both water and fire will be critical for the wise management and stewardship of California’s abundant natural resources as far into the future as any of us can imagine (i.e., our kids’ kids’ kids’ kids, etc.). In order to do this well, we first need good data. These data (and the understanding built from them) are worth investing in now (and continuing to invest in over time). Even if we don’t see or realize the immediate benefits of this investment, I believe our kids’ kids’ kids’ kids one day will be thankful we made it.

This blog is the second in a two-part series evaluating impacts of wildfire on streamflows. This first blog introduced the research question, study approach, and geographic context, and identified similar pre- and post-fire precipitation events. This second final blog will analyze streamflows resulting from the pre- and post-fire precipitation events and summarize and reflect on the findings.

Brandon Ertis is a Senior Engineer at Davids Engineering and a proud UC Davis graduate. After living in Chico for the better part of a decade, he now lives in the Sierra Nevada mountains of California, within walking distance of Lake Tahoe (albeit a pretty long walk) with his beautiful wife and two wonderful kids. He thinks life is a big messy adventure that is full of meaning and purpose.

Study design, data analysis, and development of materials were led by Brandon Ertis but with notable contributions from Davids Engineering team members Ji Yeow Law, Dylan Diep, and Gento Shimamura. Let the record note that Gento Shimamura is also a UC Davis graduate 😊.

  1. All USGS streamflow data were marked as final (rather than provisional), meaning they had been reviewed and finalized, per USGS standards.

  2. Within this first peak flow from the post-fire event, Deer and Mill Creeks both have two distinct peak flows, whereas Battle Creek only has one peak flow (similar to the pre-fire runoff). The first peak of Deer and Mill Creeks occur at the same hour (preceding Battle Creek’s peak flow by 2 hours), flows decrease afterwards, but then increase again to an even higher peak flow several hours later (a substantially higher flow on Deer Creek, 48% higher than the first peak).

  3. Additionally, as described earlier, the post-fire runoff from impacted watersheds not only peaked at higher flow levels, but also peaked more quickly than the Battle Creek watershed (which was least impacted by fire).

  4. Although the population along Battle, Deer, and Mill Creeks is small and total flooding impacts may be correspondingly small, the effects on these small communities could still be severe.

  5. The Big Chico Creek watershed was included in our introductory materials last week, but excluded from the analysis due to a lack of recent, accurate streamflow data.

Börk, Karrigan (2025). California Water under a Trump Administration (2025). California Water Blog, published in two parts: January 12, 2025 and January 19, 2025. Available at:

Grenier, Letitia and Jeffrey Mount (2025). California’s water partnerships are effective and in danger. CalMatters: California Voices Commentary. December 8, 2025. https://calmatters.org/commentary/2025/12/california-water-partnerships-disaster-cuts/

Liu, Zhu and Jonathan D. Herman, Guobiao Huang, Tariq Kadir, Helen E. Dahlke (2021). Identifying climate change impacts on surface water supply in the southern Central Valley, California. Science of The Total Environment, Volume 759, 2021, 143429, ISSN 0048-9697. https://doi.org/10.1016/j.scitotenv.2020.143429 .

Pitzer, Gary (2019). Understanding Streamflow Is Vital to Water Management in California, But Gaps In Data Exist. Water Education Foundation Website Post. Published on October 24, 2019. Available at: https://www.watereducation.org/western-water/understanding-streamflow-vital-water-management-california-gaps-data-exist

Turco, M., Abatzoglou, J.T., Herrera, S., Zhuang, Y., Jerez, S., Lucas, D.D., AghaKouchak, A., & Cvijanovic, I. Anthropogenic climate change impacts exacerbate summer forest fires in California, Proc. Natl. Acad. Sci. U.S.A. 120 (25) e2213815120, https://doi.org/10.1073/pnas.2213815120 (2023).

United States Census Bureau (USCB). Quick Facts for City of Chico, California. Available at: https://www.census.gov/quickfacts/fact/table/chicocitycalifornia# . Note: Estimated population in 2010 Census was about 86,000 people and in the 2020 Census was about 101,000 people.

For additional information and another perspective on California fire (and occasionally water, and from another Chico local), check out The Lookout:

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