View source for Wildfire and water

==Overview==

[[File:DragonBravoFire.jpg|thumb|600px|Figure 1. Smoke plume from the Dragon Bravo Fire over the Grand Canyon on July 11, 2025. (Photo: National Park Service/M. Quinn)]]

Watersheds across the western United States are being increasingly impacted by wildfires. Since 2000, West-wide average annual burned area has more than doubled, and the number of "megafires" (>100,000 acres) has increased from about one per year to over five per year.<ref name="williams2025" /> Overall, wildfires are also spreading faster, burning at higher overall severity, and at higher average elevations than in the 1980s and 1990s.<ref name="parks2023" /><ref name="alizadeh2021" /> In the Colorado River Basin, many large high-severity wildfires have impacted runoff-generating watersheds (Table 1, below), from the subalpine spruce-fir and lodgepole forests of Colorado, Utah, and Wyoming, to the ponderosa pine and mixed-conifer forests of Arizona (Figure 1) and New Mexico.<ref name="mcgrath2023" /><ref name="kampf2022" />
The dramatic shifts in wildfire occurrence and severity in the past several decades have multiple causes, including warming and drying of the atmosphere and vegetation due to anthropogenic climate change, increases in fuel loading and forest density from past forest uses and fire suppression, and increases in development in the wildland-urban interface (WUI) and in wildland recreation, leading to additional structural fuels and more opportunities for ignition during periods of high fire danger.<ref name="parks2020" /><ref name="boisrame2022" /><ref name="higuera2023" />

Wildfires can affect the basin's water resources and complicate their management in two interrelated ways: (1) altering water supply by changing snowpack accumulation and timing, plant water use, soil infiltration, and overall runoff efficiency, and (2) impairing water quality by mobilizing sediment, organic carbon, metals, and nutrients into the stream. Preventative forest management (e.g., fuels mitigation) can be undertaken to reduce wildfire impacts. These forest treatments can themselves affect watershed hydrology, depending on their intensity and scale.

===Notable recent wildfires in the Colorado River Basin===

The table below summarizes selected large wildfires since 2000 that have impacted the basin's water resources. 

'''Table 1. Selected Large Wildfires in the Colorado River Basin since 2000'''

{| class="wikitable"
! Fire
! Year
! Size (acres)
! Location
! Water-related impacts
|-
| Wallow
| 2011
| 538,049
| White Mountains, Arizona (Salt River)
| Altered summer streamflow, high peak flows and flood events, water quality impacts.
|-
| Rodeo–Chediski
| 2002
| 468,638
| White Mountains/Mogollon Rim, Arizona (Salt River)
| Changes in evapotranspiration in previously forested areas; elevated nitrogen (N), phosphorus (P), arsenic (As), lead (Pb), copper (Cu), and iron (Fe) documented in the Salt River at Roosevelt Lake.
|-
| Whitewater–Baldy
| 2012
| 297,845
| Gila National Forest, New Mexico (Gila River)
| Stream degradation and debris flows in the Gila River following the fire; destruction of native Gila trout habitat.
|-
| East Troublesome
| 2020
| 193,812
| Grand County, Colorado (Colorado River)
| Sediment and debris flows, harmful algal blooms, increased water treatment demands, and elevated peak runoff following precipitation events.
|-
| Dragon–Bravo
| 2025
| 145,504
| North Rim, Grand Canyon, Arizona (Colorado River)
| Reduced water supply by approximately 50%; destroyed the North Rim's only potable water system; post-fire debris flows.
|-
| Grizzly Creek
| 2020
| 32,632
| Glenwood Canyon, Colorado (Colorado River)
| High turbidity following the fire; debris flows blocked the mainstem Colorado River channel.
|-
| Dollar Ridge
| 2018
| 68,869
| Strawberry River, Utah
| Debris flows and total dissolved solids (TDS) transported into the Strawberry River and Starvation Reservoir; changes in TDS and pH impaired the fishery.
|-
| East Fork
| 2020
| 89,765
| Duchesne River, Utah
| Debris flows, damage to water lines at Moon Lake Campground, and high total dissolved solids (TDS) influxes.
|}

===Water supply impacts===

====Snowpack and timing of snowmelt and runoff====

Wildfires can alter the amount and timing of streamflows primarily by impacting the accumulation and melt of the seasonal snowpack. Large wildfires that kill some portion of the canopy (i.e., crown fire) consistently result in decreased snow-water storage and earlier timing of snowmelt.<ref name="smoot2021" /><ref name="giovando2022" /><ref name="koshkin2022" /> The loss of forest canopy alters the snowpack energy balance by increasing solar radiation reaching the snow surface, causing enhanced melt and sublimation throughout the winter and spring.<ref name="mcgrath2023" /><ref name="kampf2022" /><ref name="smoot2021" /><ref name="koshkin2022" /> Additionally, black carbon and burned woody debris shed onto the snow post-fire darkens its surface, causing greater absorption of solar radiation and accelerating melt rates.<ref name="mcgrath2023" /><ref name="koshkin2022" /><ref name="smoot2021" /><ref name="kampf2022" /> These changes in snow accumulation and melt timing are long-lived<ref name="mcgrath2023" />, persisting for at least 10 years<ref name="smoot2021" /><ref name="koshkin2022" /><ref name="giovando2022" />, and need to be factored into for water supply forecasting, planning, and management.

====Plant water use====

By causing both immediate and delayed mortality in non-woody plants, shrubs, and trees wildfires typically result in reductions to total water use (i.e., transpiration) by vegetation in the burn area.<ref name="bar2019" /><ref name="niccoli2023" /><ref name="obrien2010" /> The timing of onset, magnitude, and duration of these changes depend strongly on burn severity, vegetation type, and forest recovery mechanisms. During the period that transpiration is reduced, runoff from the burned area may increase, depending on the fire's effects on other elements of the area's water balance.

Reduced transpiration following wildfire vegetation mortality has been documented across many forest types.<ref name="dore2012" /><ref name="poon2018" /><ref name="ma2020" /> The duration of these reductions varies, but typically lasts from 2 to 15 years.<ref name="hausler2018" /><ref name="dore2012" /> In some cases, vigorous regrowth of trees post-fire ultimately leads to greater water use than in the pre-fire condition.<ref name="langford1975" /><ref name="meili2024" />

====Soil infiltration and runoff====

Wildfires also often change how water from rain and snowmelt moves through–or doesn't move through–the soil. Fires strip away the protective and water-absorbent surface litter layer, exposing bare soil, and reduce tree canopy cover that could have prevented raindrops from directly striking that soil.<ref name="wine2016" /> High-severity fires can also create a strongly water-repellent (hydrophobic) layer beneath the surface.<ref name="mataix2004" /><ref name="huffman2001" /> This hydrophobic layer inhibits rain and snowmelt from soaking into the soil, so that more of that water reaches the stream through surface runoff rather than slower groundwater processes.<ref name="wine2016" /><ref name="williams2022" /> This leads to more abrupt and higher peak stream discharges after snowmelt and rain events, with much higher risk for damaging flash floods and debris flows, and potentially also to increases in total annual water yield, depending on other factors.<ref name="wine2016" />

===Water quality impacts===

After a wildfire, large areas of soil are newly exposed to erosion. The resulting jump in sediment flux to streams and rivers, along with ash and other burned debris, causes many contaminants to exceed pre-fire concentrations by orders of magnitude.<ref name="paul2022" /> Among these contaminants is dissolved organic carbon (DOC), which can combine with the chlorine used in water treatment to form harmful chlorinated by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs).<ref name="smith2011" /><ref name="hohner2019" /> while also reducing coagulation efficiency in treatment plants.<ref name="hohner2019" /><ref name="hohner2017" />

Levels of nutrients such as nitrogen (N) and phosphorus (P) can also spike.<ref name="paul2022" /> causing algal blooms and other biological impacts.<ref name="paul2022" /><ref name="hohner2019" /> Metals such as iron (Fe), manganese (Mn), arsenic (As), lead (Pb), and copper (Cu) are often mobilized with the sediment and ash as well.<ref name="allen2005" /><ref name="kelly2006" /> While most of these water-chemistry impacts subside within five years of a wildfire, some effects, such as the persistence of nitrogen and DOC, can extend for 15 years or more following high-severity events.<ref name="hohner2019" /><ref name="paul2022" />

Beyond the chemical contaminants, the dramatically increased sediment loading in streams and rivers is itself problematic for water treatment.<ref name="paul2022" /><ref name="smith2011" /> High turbidity makes disinfection and filtration less efficient and more costly.<ref name="smith2011" /><ref name="paul2022" /> and in extreme conditions water intakes may have to be shut down completely.<ref name="hohner2019" /><ref name="writer2014" /><ref name="paul2022" /> The influx of ash and sediment also has acute effects on aquatic life.<ref name="earl2003" /><ref name="paul2022" /> often leading to declines in fish populations.<ref name="paul2022" /><ref name="rust2019" /> The altered physical and chemical conditions post-fire can drive shifts in macroinvertebrate communities towards more opportunistic species.<ref name="paul2022" />

===Land management to reduce fire risk and impacts===

Mechanical thinning and prescribed fire have been used for many years to reduce the risk of high-severity fires, particularly in mid-elevation ponderosa pine and mixed-conifer forests that have become much denser due to post-1900 fire suppression.<ref name="stephens2012" /><ref name="davis2024" /> These treatments can also improve snowpack retention<ref name="broxton2025" /><ref name="lumbrazo2026" /> and may modestly increase annual streamflow by reducing canopy interception and evapotranspiration, though sustained increases in water supply are uncertain and dependent on many local factors.<ref name="goeking2020" /><ref name="goeking2022" /> Several water providers, including Denver Water (Forests to Faucets) and Salt River Project (SRP Healthy Forests Initiative), have partnered with land managers to plan, fund, and carry out forest treatments in their Colorado River watersheds to reduce the risk of severe wildfires and their impacts to water supplies.

More recently, it has been recognized that stream and wetland restoration can bring substantial co-benefits for wildfire mitigation. Restoring the water- and sediment-retention functions of riparian and wetland areas and enlarging their footprint on the landscape can slow fire spread through "wet fuel breaks", reduce burn severity, and alleviate post-fire impacts on water quality. These restoration techniques, collectively called process-based restoration (PBR), include beaver reintroduction, emplacing logs and wood structures in stream channels such as beaver-dam analogs (BDAs), riparian plantings, meadow restoration, and, when necessary, earthmoving to reestablish natural channels and stream connectivity. 

PBR projects in the basin are often supported by water agencies in collaboration with land managers and environmental NGOs. For example, the Kawuneeche Valley Restoration Collaborative (KVRC) in the Colorado River headwaters in north-central Colorado receives direct funding and staff involvement from Northern Water as well as grants from the Colorado Water Conservation Board, Colorado River District, and Reclamation.

==Data and Tools==

<onlyinclude>
===[https://lcms-viewer.fs2c.usda.gov/mtbs USDA MTBS (Burn Severity) Data Explorer]===
Monitoring Trends in Burn Severity (MTBS) is an interagency program to map the burn severity and extent of large wildfires (>1,000 acres in the West) based on satellite imagery. When opened, the MTBS Data Explorer will show the perimeter and per-pixel burn severity of all large fires from 1984 through 2024. To see the name, ignition date, and acreage of a fire, select Tools > Pixel Tools > Query Visible Map Layers and then click within a fire perimeter. 

===[https://egp.wildfire.gov/maps/incidents NIFC WildfireSA Public Map]===
This interactive map from the National Interagency Fire Center (NIFC) shows all current and recent wildfires (‘incidents’). Click on a fire to bring up more information about that fire. From the Layers button in the upper right, you can also select ‘Fuels Treatments’ to show all recent (>2000) management actions to reduce fuels.  

===[https://apps.usgs.gov/landslides/pwfdf/ USGS Post-Fire Debris Flow Hazard Assessment Viewer]===
The USGS produces rapid postfire debris-flow hazard assessments for select fires in the Western U.S., using geospatial data on basin slopes, burn severity, soil properties, and rainfall characteristics to estimate the likelihood and volume of debris flows that may occur in response to a defined rainstorm (typically 0.25”-0.5” in 15 minutes, corresponding to a once-in-1-year event).
</onlyinclude>
==Additional Resources==

===[https://iopscience.iop.org/article/10.1088/3033-4942/ae2a64/meta A review of post-wildfire shifts in streamflow]===

This 2025 review paper by Ebel et al. synthesizes existing research on how wildfire alters hydrologic processes and streamflow generation in the western United States. It presents a narrative review and conceptual model highlighting the key factors that shape post-fire changes in streamflow such as seasonal precipitation, the timing overlap between precipitation and potential evapotranspiration, shifts in interception and evapotranspiration relative to overall precipitation, and vegetation-related changes. 

==Notes==
<references>
<ref name="mcgrath2023">McGrath, D., Zeller, L., Bonnell, R., Reis, W., Kampf, S., Williams, K., ... & Rittger, K. (2023). ''Declines in peak snow water equivalent and elevated snowmelt rates following the 2020 Cameron Peak wildfire in northern Colorado.'' Geophysical Research Letters, 50(6), e2022GL101294.</ref>

<ref name="kampf2022">Kampf, S. K., McGrath, D., Sears, M. G., Fassnacht, S. R., Kiewiet, L., & Hammond, J. C. (2022). ''Increasing wildfire impacts on snowpack in the western US.'' Proceedings of the National Academy of Sciences, 119(39), e2200333119.</ref>

<ref name="alizadeh2021">Alizadeh, M. R., Abatzoglou, J. T., Luce, C. H., Adamowski, J. F., Farid, A., & Sadegh, M. (2021). Warming enabled upslope advance in western US forest fires. Proceedings of the National Academy of Sciences, 118(22), e2009717118.</ref>

<ref name="smoot2021">Smoot, E. E., & Gleason, K. E. (2021). ''Forest fires reduce snow-water storage and advance the timing of snowmelt across the Western US.'' Water, 13(24), 3533.</ref>

<ref name="giovando2022">Giovando, J., & Niemann, J. D. (2022). ''Wildfire impacts on snowpack phenology in a changing climate within the western US.'' Water Resources Research, 58(8), e2021WR031569.</ref>

<ref name="koshkin2022">Koshkin, A. L., Hatchett, B. J., & Nolin, A. W. (2022). ''Wildfire impacts on western United States snowpacks.'' Frontiers in Water, 4, 971271.</ref>

<ref name="bar2019">Bär, A., Michaletz, S. T., & Mayr, S. (2019). ''Fire effects on tree physiology.'' New Phytologist, 223(4), 1728–1741.</ref>

<ref name="niccoli2023">Niccoli, F., Pacheco-Solana, A., Delzon, S., et al. (2023). ''Effects of wildfire on growth, transpiration and hydraulic properties of Pinus pinaster Aiton forest.'' Dendrochronologia, 79, 126086.</ref>

<ref name="obrien2010">O'Brien, J. J., Kevin Hiers, J., Mitchell, R. J., Varner III, J. M., & Mordecai, K. (2010). ''Acute physiological stress and mortality following fire in a long-unburned longleaf pine ecosystem.'' Fire Ecology, 6(2), 1–12.</ref>

<ref name="dore2012">Dore, S., Montes-Helu, M., Hart, S. C., et al. (2012). ''Recovery of ponderosa pine ecosystem carbon and water fluxes from thinning and stand-replacing fire.'' Global Change Biology, 18(10), 3171–3185.</ref>

<ref name="poon2018">Poon, P. K., & Kinoshita, A. M. (2018). ''Spatial and temporal evapotranspiration trends after wildfire in semi-arid landscapes.'' Journal of Hydrology, 559, 71–83.</ref>

<ref name="ma2020">Ma, Q., Bales, R. C., Rungee, J., et al. (2020). ''Wildfire controls on evapotranspiration in California's Sierra Nevada.'' Journal of Hydrology, 590, 125364.</ref>

<ref name="hausler2018">Häusler, M., Nunes, J. P., Soares, P., et al. (2018). ''Assessment of the indirect impact of wildfire (severity) on actual evapotranspiration in eucalyptus forest based on the surface energy balance estimated from remote-sensing techniques.'' International Journal of Remote Sensing, 39(20), 6499–6524.</ref>

<ref name="langford1975">Langford, K. J. (1975). ''Change in yield of water following a bushfire in a forest of Eucalyptus regnans.'' Report No. MMBW-W-0003.</ref>

<ref name="meili2024">Meili, N., Beringer, J., Zhao, J., & Fatichi, S. (2024). ''Aerodynamic effects cause higher forest evapotranspiration and water yield reductions after wildfires in tall forests.'' Global Change Biology, 30(1), e16995.</ref>

<ref name="wine2016">Wine, M. L., & Cadol, D. (2016). ''Hydrologic effects of large southwestern USA wildfires significantly increase regional water supply: Fact or fiction?'' Environmental Research Letters, 11(8), 085006.</ref>

<ref name="mataix2004">Mataix-Solera, J., & Doerr, S. H. (2004). ''Hydrophobicity and aggregate stability in calcareous topsoils from fire-affected pine forests in southeastern Spain.'' Geoderma, 118(1–2), 77–88.</ref>

<ref name="huffman2001">Huffman, E. L., MacDonald, L. H., & Stednick, J. D. (2001). ''Strength and persistence of fire-induced soil hydrophobicity under ponderosa and lodgepole pine, Colorado Front Range.'' Hydrological Processes, 15(15), 2877–2892.</ref>

<ref name="williams2022">Williams, A. P., Livneh, B., McKinnon, K. A., Hansen, W. D., Mankin, J. S., Cook, B. I., ... & Lettenmaier, D. P. (2022). ''Growing impact of wildfire on western US water supply.'' Proceedings of the National Academy of Sciences, 119(10), e2114069119.</ref>

<ref name="paul2022">Paul, M. J., LeDuc, S. D., Lassiter, M. G., Moorhead, L. C., Noyes, P. D., & Leibowitz, S. G. (2022). ''Wildfire induces changes in receiving waters: A review with considerations for water quality management.'' Water Resources Research, 58(9), e2021WR030699.</ref>

<ref name="smith2011">Smith, H. G., Sheridan, G. J., Lane, P. N., Nyman, P., & Haydon, S. (2011). ''Wildfire effects on water quality in forest catchments: A review with implications for water supply.'' Journal of Hydrology, 396(1–2), 170–192.</ref>

<ref name="hohner2019">Hohner, A. K., Rhoades, C. C., Wilkerson, P., & Rosario-Ortiz, F. L. (2019). ''Wildfires alter forest watersheds and threaten drinking water quality.'' Accounts of Chemical Research, 52(5), 1234–1244.</ref>

<ref name="hohner2017">Hohner, A. K., Terry, L. G., Townsend, E. B., Summers, R. S., & Rosario-Ortiz, F. L. (2017). ''Water treatment process evaluation of wildfire-affected sediment leachates.'' Environmental Science: Water Research & Technology, 3(2), 352–365.</ref>

<ref name="allen2005">Allen, E. W., Prepas, E. E., Gabos, S., Strachan, W. M., & Zhang, W. (2005). ''Methyl mercury concentrations in macroinvertebrates and fish from burned and undisturbed lakes on the Boreal Plain.'' Canadian Journal of Fisheries and Aquatic Sciences, 62(9), 1963–1977.</ref>

<ref name="kelly2006">Kelly, E. N., Schindler, D. W., St. Louis, V. L., Donald, D. B., & Vladicka, K. E. (2006). ''Forest fire increases mercury accumulation by fishes via food web restructuring and increased mercury inputs.'' Proceedings of the National Academy of Sciences, 103(51), 19380–19385.</ref>

<ref name="writer2014">Writer, J. H., Hohner, A., Oropeza, J., Schmidt, A., Cawley, K. M., & Rosario-Ortiz, F. L. (2014). ''Water treatment implications after the High Park wildfire, Colorado.'' Journal ‐ American Water Works Association, 106(4), E189–E199.</ref>

<ref name="earl2003">Earl, S. R., & Blinn, D. W. (2003). ''Effects of wildfire ash on water chemistry and biota in south-western USA streams.'' Freshwater Biology, 48(6), 1015–1030.</ref>

<ref name="rust2019">Rust, A. J., Saxe, S., McCray, J., Rhoades, C. C., & Hogue, T. S. (2019). ''Evaluating the factors responsible for post-fire water quality response in forests of the western USA.'' International Journal of Wildland Fire, 28(10), 769–784.</ref>

<ref name="williams2025">Williams, A. P., Juang, C. S., & Short, K. C. (2025). The Western United States MTBS-Interagency database of large wildfires, 1984–2024 (WUMI2024a). Earth Syst. Sci. Data, 17(12), 7359–7372. https://doi.org/10.5194/essd-17-7359-2025</ref>

<ref name="parks2023">Parks, S. A., Holsinger, L. M., Blankenship, K., Dillon, G. K., Goeking, S. A., & Swaty, R. (2023). Contemporary wildfires are more severe compared to the historical reference period in western US dry conifer forests. Forest Ecology and Management, 544, 121232. https://doi.org/10.1016/j.foreco.2023.121232</ref>

<ref name="boisrame2022">Boisramé, G. F. S., Brown, T. J., & Bachelet, D. M. (2022). Trends in western USA fire fuels using historical data and modeling. Fire Ecology, 18(1), 8. https://doi.org/10.1186/s42408-022-00129-4</ref>

<ref name="higuera2023">Higuera, P. E., Cook, M. C., Balch, J. K., Stavros, E. N., Mahood, A. L., & St. Denis, L. A. (2023). Shifting social-ecological fire regimes explain increasing structure loss from Western wildfires. PNAS Nexus, 2(3), pgad005. https://doi.org/10.1093/pnasnexus/pgad005</ref>

<ref name="parks2020">Parks, S. A., & Abatzoglou, J. T. (2020). Warmer and Drier Fire Seasons Contribute to Increases in Area Burned at High Severity in Western US Forests From 1985 to 2017. Geophysical Research Letters, 47(22). https://doi.org/10.1029/2020GL089858</ref>

<ref name="davis2024">Davis, K. T., Peeler, J., Fargione, J., Haugo, R. D., Metlen, K. L., Robles, M. D., & Woolley, T. (2024). Tamm review: A meta-analysis of thinning, prescribed fire, and wildfire effects on subsequent wildfire severity in conifer dominated forests of the Western US. Forest Ecology and Management, 561, 121885. https://doi.org/10.1016/j.foreco.2024.121885</ref>

<ref name="stephens2012">Stephens, S. L., McIver, J. D., Boerner, R. E. J., Fettig, C. J., Fontaine, J. B., Hartsough, B. R., Kennedy, P. L., & Schwilk, D. W. (2012). The Effects of Forest Fuel-Reduction Treatments in the United States. BioScience, 62(6), 549–560. https://doi.org/10.1525/bio.2012.62.6.6</ref>

<ref name="broxton2025">Broxton, P. D., Biederman, J. A., Dwivedi, R., Van Leeuwen, W. J. D., Sankey, T. Ts., Woolley, T., & Svoma, B. M. (2025). Forest Patch Geometry and Climate Regulate the Impact of Forest Thinning on Snowpack in the Southwest United States. Ecohydrology, 18(6), e70111. https://doi.org/10.1002/eco.70111</ref>

<ref name="goeking2020">Goeking, S. A., & Tarboton, D. G. (2020). Forests and Water Yield: A Synthesis of Disturbance Effects on Streamflow and Snowpack in Western Coniferous Forests. Journal of Forestry, 118(2), 172–192. https://doi.org/10.1093/jofore/fvz069</ref>

<ref name="goeking2022">Goeking, S. A., & Tarboton, D. G. (2022). Variable Streamflow Response to Forest Disturbance in the Western US: A Large‐Sample Hydrology Approach. Water Resources Research, 58(6), e2021WR031575. https://doi.org/10.1029/2021WR031575</ref>

<ref name="lumbrazo2026">Lumbrazo, C., Howe, E. R., Dickerson-Lange, S. E., Pestana, S., Cramblitt, J., Dedinsky, K., Smith, K., & Lundquist, J. D. (2026). Can we maximize snow storage through fire-resilient forest treatments? Insights from experimental forest treatments in the Eastern Cascades, WA, USA. Frontiers in Forests and Global Change, 8, 1707812. https://doi.org/10.3389/ffgc.2025.1707812</ref>


</references>