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At least 307 records · Page 17Linked to original sources
USGS2023

The influence of large woody debris on post-wildfire debris flow sediment storage

Debris flows transport large quantities of water and granular material, such as sediment and wood, and this mixture can have devastating impacts on life and infrastructure. The proportion of large woody debris (LWD) incorporated into debris flows can be enhanced in forested areas recently burned by wildfire, because wood recruitment into channels accelerates in burned forests. In this study, we explored how LWD transported in post-wildfire debris flows acts to retain sediment within small headwater channels. We found that the largest amount of debris flow sediment is stored in channel reaches with a ratio of LWD length to channel width between 0.25 and 1. Moreover, the largest debris flow deposits forced by LWD were found in low-angle channel reaches. We examined two models for debris flow volume estimation: (1) the current volume prediction model used in U.S. Geological Survey debris flow hazard assessments, and (2) a regional model developed to predict the sediment yield associated with debris-laden flows. We found that the regional model better matched the magnitude of the observed sediment at the terminal fan, suggesting the utility of regionally calibrated parameters for debris flow volume prediction. However, large wood created sediment storage upstream of the terminal fan, and this volume was of the same magnitude as the total volume at the terminal fans. Finally, we demonstrate a method for estimating debris flow velocity based on estimates of the critical velocity required to break wood, which can be used in future field studies to estimate minimum debris flow velocity values.

New Mexico↗
USGS2002

Long lead statistical forecasts of area burned in western U.S. wildfires by ecosystem province

A statistical forecast methodology exploits large-scale patterns in monthly U.S. Climatological Division Palmer Drought Severity Index (PDSI) values over a wide region and several seasons to predict area burned in western U.S. wildfires by ecosystem province a season in advance. The forecast model, which is based on canonical correlations, indicates that a few characteristic patterns determine predicted wildfire season area burned. Strong negative associations between anomalous soil moisture (inferred from PDSI) immediately prior to the fire season and area burned dominate in most higher elevation forested provinces, while strong positive associations between anomalous soil moisture a year prior to the fire season and area burned dominate in desert and shrub and grassland provinces. In much of the western U.S., above- and below-normal fire season forecasts were successful 57% of the time or better, as compared with a 33% skill for a random guess, and with a low probability of being surprised by a fire season at the opposite extreme of that forecast.

Conference Paper↗
USGS2003

Wildfire-related debris-flow generation through episodic progressive sediment-bulking processes, western USA

Debris-flow initiation processes on hillslopes recently burned by wildfire differ from those generally recognized on unburned, vegetated hillslopes. These differences result from fire-induced changes in the hydrologic response to rainfall events. In this study, detailed field and aerial photographic mapping, observations, and measurements of debris-flow events from three sites in the western U.S. are used to describe and evaluate the process of episodic progressive sediment bulking of storm runoff that leads to the generation of post-wildfire debris flows. Our data demonstrate the effects of material credibility, sediment availability on hillslopes and in channels, the degree of channel confinement, the formation of continuous channel incision, and the upslope contributing area and its gradient on the generation of flows and the magnitude of the response are demonstrated. ?? 2003 Millpress.

Conference Paper↗
USGS2018

Quantifying post-wildfire hillslope erosion with lidar

Following a wildfire, flooding and debris- flow hazards are common and pose a threat to human life and infrastructure in steep burned terrain. Wildfire enhances both water runoff and soil erosion, which ultimately shape the debris flow potential. The erosional processes that route excess sediment from hillslopes to debris-flow channels in recently burned areas, however, are poorly constrained. In this study we examined erosional processes through repeat terrestrial lidar surveys in a steep mountainous watershed that experienced a high-severity burn in the 2016 San Gabriel complex fire. Three lidar surveys were conducted during a wet winter (2016-2017) on a hillslope plot. We used geomorphometric techniques to better contextualize erosion observations in areas with rills and between rills (interrill areas). A challenge was effectively differentiating DEM pixels that were in the constantly evolving rill network as well as those outside the rill network. By applying a series of DEM filtering processes we found that it was possible to efficiently identify the small-scale rill networks. Our results challenge previously held beliefs about sediment erosion on burned hillslopes, suggesting that prior estimates made without access to high resolution topography likely underestimated the role of interrill erosion.

Conference Paper↗
USGS2019

Characterization of hydrology and sediment transport following drought and wildfire in Cache Creek, California

The worst drought in California in over 1,200 years occurred between 2012-2017 (Griffin, 2014), depleting surface water and groundwater supply and drying out the soils past wilting point. In the summer of 2015, the Jerusalem and Rocky fires burned roughly 40,000 acres within the Cache Creek watershed. To fully characterize the post-fire effects in the Cache Creek watershed, an hourly model of streamflow and sediment transport was developed using the Hydrological Simulation Program – FORTRAN (HSPF). This model requires air temperature, precipitation, and potential evapotranspiration as climate inputs. Hourly station data are sparse in the area and may not capture the variability of elevation and local climatology patterns within the watershed. A technique used previously to spatially-interpolate daily-climate station data has improved the characterization of local and regional climate patterns on a daily scale in areas with sparse data (Flint et al., 2014). This technique was extended to hourly observed data to produce spatially-varying climate inputs for the Cache Creek hydrologic model to run as a continuous multi-year simulation with hourly time steps. Monthly PRISM grids were used in a two-step scaling method with climate Gradient and Inverse Distance Squared (GIDS) maps (Nalder and Wein, 1998) to develop daily grids, then the daily grids were used to scale hourly climate GIDS maps. This method captures the temporal variability at each climate station yet preserves the regional monthly spatial structure of the PRISM data. Hydrologic calibration used data from water year 2015, and validation used the same parameters for water year 2016. The model was run through water year 2017 to characterize the effects of wildfire on hydrology and sediment transport. For final simulations, the model was run at an hourly time step from June 2014 through September 2017 to ensure a model initiation period of 4 months prior to the target simulation period used for analysis. Sediment parameters were initially set using the existing Sacramento River Basin model for this sub-watershed area and then iteratively adjusted in the calibration process. To simulate a fire across the landscape, sediment parameters for water years 2016-17 were further modified for burned sub-basins to represent post-fire vegetation and soils in 2016, then partial recovery in 2017. Results were inconclusive for drought and wildfire effects on runoff. Modeled peak flows generally underpredicted observed peak flows; however, the modeled storm volumes were only slightly under or over the observed storm volumes. Sediment transport was sensitive to the watershed disturbances and R^2 values for daily mean suspended concentrations (SSC) and sediment discharge were 0.70 and 0.75, respectively. Simulated hourly values correlated less strongly with observed instantaneous SSC and sediment discharge (R^2 values of 0.56 and 0.46, respectively).

California↗
USGS2022

Spreading like wildfire: The rising threat of extraordinary landscape fires - A rapid response assessment

Free-burning landscape fire is an important natural phenomenon critical to the healthy functioning of many ecosystems. It is an important land management tool, culturally, economically, and ecologically. Therefore, not all vegetation fires are unwanted. This Rapid Response Assessment (RRA) focuses on the apparent increase in the occurrence, extent, duration, and consequences of wildfires – unusual or extraordinary free-burning vegetation fires. The RRA considers the changing patterns of wildfires around the world, their impact on people and the environment, and options for mitigating risk and improving our response.

Book↗
USGS2024

Learning from the past and planning for the future: Experience-driven insight into managing for ecosystem transformations induced by drought and wildfire

Drought and wildfire pose enormous threats to the integrity of natural resources that land managers are charged with protecting. Recent observations and modeling forecasts indicate that these stressors will likely produce catastrophic ecosystem transformations, or abrupt changes in the condition of plants, wildlife, and their habitats, in regions across the country in coming decades. In this project, researchers will bring together land managers who have experienced various degrees of ecosystem transformation (from not yet experiencing any changes to seeing large changes across the lands they manage) to share their perspectives on how to mitigate large-scale changes in land condition. The team will conduct surveys and structured interviews and invite participants to an in-person field trip and workshop. Encouraging land managers to share perspectives across diverse ecosystems with different degrees of drought and wildfire stress will produce new insight into how to better prevent and prepare for ecosystem changes. New knowledge generated from this project will be widely shared with land managers throughout the western U.S. to improve climate adaptation decision making processes.

Final Report↗
USGS2017

Climate changes and wildfire alter vegetation of Yellowstone National Park, but forest cover persists

We present landscape simulation results contrasting effects of changing climates on forest vegetation and fire regimes in Yellowstone National Park, USA, by mid-21st century. We simulated potential changes to fire dynamics and forest characteristics under three future climate projections representing a range of potential future conditions using the FireBGCv2 model. Under the future climate scenarios with moderate warming (>2°C) and moderate increases in precipitation (3–5%), model simulations resulted in 1.2–4.2 times more burned area, decreases in forest cover (10–44%), and reductions in basal area (14–60%). In these same scenarios, lodgepole pine ( Pinus contorta ) decreased in basal area (18–41%), while Douglas-fir ( Pseudotsuga menziesii ) basal area increased (21–58%). Conversely, mild warming (<2°C) coupled with greater increases in precipitation (12–13%) suggested an increase in forest cover and basal area by mid-century, with spruce and subalpine fir increasing in abundance. Overall, we found changes in forest tree species compositions were caused by the climate-mediated changes in fire regime (56–315% increase in annual area burned). Simulated changes in forest composition and fire regime under warming climates portray a landscape that shifts from lodgepole pine to Douglas-fir caused by the interaction between the magnitude and seasonality of future climate changes, by climate-induced changes in the frequency and intensity of wildfires, and by tree species response.

Wyoming↗
USGS2024

Assessing giant sequoia mortality and regeneration following high-severity wildfire

Fire is a critical driver of giant sequoia ( Sequoiadendron giganteum [Lindl.] Buchholz) regeneration. However, fire suppression combined with the effects of increased temperature and severe drought has resulted in fires of an intensity and size outside of the historical norm. As a result, recent mega-fires have killed a significant portion of the world's sequoia population (13%–19%), and uncertainty surrounds whether severely affected groves will be able to recover naturally, potentially leading to a loss of grove area. To assess the likelihood of natural recovery, we collected spatially explicit data assessing mortality, crown condition, and regeneration within four giant sequoia groves that were severely impacted by the SQF- (2020) and KNP-Complex (2021) wildfires within Sequoia and Kings Canyon National Parks. In total, we surveyed 5.9 ha for seedlings and assessed the crown condition of 1104 giant sequoias. To inform management, we used a statistical methodology that robustly quantifies the uncertainty in inherently “noisy” seedling data and takes advantage of readily available remote sensing metrics that would make our findings applicable to other recently burned groves. A loss of giant sequoia grove area would be a consequence of giant sequoia tree mortality followed by a failure of natural regeneration. We found that areas that experienced very high-severity fire (above ~800 RdNBR) are at substantial risk for the loss of grove area, with tree mortality rapidly increasing and giant sequoia seedling density simultaneously decreasing with fire severity. Such high-severity areas comprised 17.8, 142.0, 14.6, 1.6 ha and ~90%, ~14%, ~53%, and ~27% of Board Camp, Redwood Mountain, Suwanee, and New Oriole Lake groves, respectively. In all sampling areas, we found that seedling densities fell far below the average density measured after prescribed fires, where seedling numbers were almost certainly adequate to maintain giant sequoia populations and postfire conditions were more in keeping with historical norms. Importantly, spatial pattern is also important in assessing the risk of grove loss, and in two groves, Suwanee and New Oriole Lake, the high-severity patches were not always contiguous, potentially making some areas more resilient to regeneration failure due to the proximity of surviving trees.

Ecosphere↗
USGS2018

Incorporating spatially heterogeneous infiltration capacity into hydrologic models with applications for simulating post‐wildfire debris flow initiation

Soils in post‐wildfire environments are often characterized by a low infiltration capacity with a high degree of spatial heterogeneity relative to unburned areas. Debris flows are frequently initiated by run‐off in recently burned steeplands, making it critical to develop and test methods for incorporating spatial variability in infiltration capacity into hydrologic models. We use Monte Carlo simulations of run‐off generation over a soil with a spatially heterogenous saturated hydraulic conductivity ( K s ) to derive an expression for an aerially averaged saturated hydraulic conductivity ( ) that depends on the rainfall rate, the statistical properties of K s , and the spatial correlation length scale associated with K s . The proposed method for determining is tested by simulating run‐off on synthetic topography over a wide range of spatial scales. Results provide a simplified expression for an effective saturated hydraulic conductivity that can be used to relate a distribution of small‐scale K s measurements to infiltration and run‐off generation over larger spatial scales. Finally, we use a hydrologic model based on to simulate run‐off and debris flow initiation at a recently burned catchment in the Santa Ana Mountains, CA, USA, and compare results to those obtained using an infiltration model based on the Soil Conservation Service Curve Number.

California↗
USGS2007

Linking runoff response to burn severity after a wildfire

Extreme floods often follow wildfire in mountainous watersheds. However, a quantitative relation between the runoff response and burn severity at the watershed scale has not been established. Runoff response was measured as the runoff coefficient C, which is equal to the peak discharge per unit drainage area divided by the average maximum 30 min rainfall intensity during each rain storm. The magnitude of the bum severity was expressed as the change in the normalized burn ratio. A new burn severity variable, hydraulic functional connectivity ?? was developed and incorporates both the magnitude of the burn severity and the spatial sequence of the bum severity along hillslope flow paths. The runoff response and the burn severity were measured in seven subwatersheds (0.24 to 0.85 km2) in the upper part of Rendija Canyon burned by the 2000 Cerro Grande Fire Dear Los Alamos, New Mexico, USA. A rainfall-discharge relation was determined for four of the subwatersheds with nearly the same bum severity. The peak discharge per unit drainage area Qupeak was a linear function of the maximum 30 min rainfall intensity I30. This function predicted a rainfall intensity threshold of 8.5 mm h-1 below which no runoff was generated. The runoff coefficient C = Qupeak/I30 was a linear function of the mean hydraulic functional connectivity of the subwatersheds. Moreover, the variability of the mean hydraulic functional connectivity was related to the variability of the mean runoff coefficient, and this relation provides physical insight into why the runoff response from the same subwatershed can vary for different rainstorms with the same rainfall intensity. Published in 2007 by John Wiley & Sons, Ltd.

Hydrological Processes↗
USGS2025

Variability in hydrologic response to wildfire between snow zones in forested headwaters

Rising temperatures and shifting fire regimes in the western United States are pushing fires upslope into areas of deep winter snowpack, where we have little knowledge of the likely hydrologic impacts of wildfire. We quantified differences in the timing and magnitude of stormflow responses to summer rainstorms among six catchments of varying levels of burn severity and seasonal snowpack cover for years 1–3 after the 2020 Cameron Peak fire. Our objectives were to (1) examine whether responsiveness, magnitude, and timing of stormflow responses to rainfall vary between burned and unburned catchments and between snow zones, and (2) identify the factors that affect these responses. We evaluated whether differences in storm hydrograph peak flow, total flow, stage rise, and lag to peak time differed by snow zone and burn category using generalised linear models. Additional predictors in these models are the maximum 60-min rainfall intensity for each storm, the cumulative potential water deficit prior to the storm, and the year post-fire. These models showed that the high snow zone (HSZ) has higher total stormflow than the low snow zone (LSZ), likely due to the higher soil moisture content in that area. In both snow zones, the biggest driver of the magnitude of the stormflow response was MI 60 . Burn category did not have a clear impact on stormflow response in the HSZ, but it did impact stage rise at the severely burned catchment in the LSZ. This was the only site that had widespread overland flow post-fire. These results demonstrate that the stormflow responses to fire vary between snow zones, indicating a need to account for elevation and snow persistence in post-fire risk assessments.

Colorado↗
USGS2008

Effects of 2003 wildfires on stream chemistry in Glacier National Park, Montana

Changes in stream chemistry were studied for 4 years following large wildfires that burned in Glacier National Park during the summer of 2003. Burned and unburned drainages were monitored from December 2003 through August 2007 for streamflow, major constituents, nutrients, and suspended sediment following the fires. Stream-water nitrate concentrations showed the greatest response to fire, increasing up to tenfold above those in the unburned drainage just prior to the first post-fire snowmelt season. Concentrations in winter base flow remained elevated during the entire study period, whereas concentrations during the growing season returned to background levels after two snowmelt seasons. Annual export of total nitrogen from the burned drainage ranged from 1·53 to 3·23 kg ha −1 yr −1 compared with 1·01 to 1·39 kg ha −1 yr −1 from the unburned drainage and exceeded atmospheric inputs for the first two post-fire water years. Fire appeared to have minimal long-term effects on other nutrients, dissolved organic carbon, and major constituents with the exception of sulfate and chloride, which showed increased concentrations for 2 years following the fire. There was little evidence that fire affected suspended-sediment concentrations in the burned drainage. Sediment yields in subalpine streams may be less affected by fire than in lower elevation streams because of the slow release rate of water during spring snowmelt.

Hydrological Processes↗
USGS2019

Effects of historic wildfire and prescribed fire on site occupancy of bats in Shenandoah National Park, Virginia, USA

Given high likelihood of regional extirpation of several once-common bat species in eastern North America from White-nose Syndrome, it is critical that impacts of forest management activities such as prescribed fire are known to minimize potentially additive negative effects on bat populations. Historic wildfires may offer a suitable surrogate to assess long-term burn impacts on bats for planning, implementing and assessing burning programs going forward. To examine effects of historic fire on bats, we sampled bat activity at 24 transect locations in burned and unburned forest stands in the central Appalachian Mountains of Shenandoah National Park (SNP), Virginia, USA, 2015. We found limited evidence positive fire effects over time on hoary bats (Lasiurus cinereus) and big brown bats (Eptesicus fuscus) occupancy. Overall, we found few or mostly equivocal relationships of bat occupancy relative to burn condition or time since fire at SNP across species using a false-positive occupancy approach. Our results suggest that fire does not strongly affect bat site occupancy at short or long-term time scales in the central Appalachians.

Virginia↗
USGS2004

Wildfire-resistant biological soil crusts and fire-induced loss of soil stability in Palouse prairies, USA

Frequent low-intensity fires are a natural component of the ecology of the Palouse prairies of northwestern North America. To study the effects of fire upon biological soil crusts (BSCs) occurring in these grasslands, we sampled three burned (in 2000) sites and three unburned sites in the Hell's Canyon area (OR, USA) ???1 year post-fire. We measured vascular plant and BSC cover, soil microbe pigmentation, texture and chemistry, and soil surface physical properties (stability and rugosity). Festuca idahoensis was two times more abundant in unburned plots (P=0.0006), and vascular plant and litter cover were generally higher in unburned plots. At the community scale, there was no difference in the lichen and moss species composition, suggesting much less drastic effects of fire on BSCs than reported in other systems. Soil surface stability (measured using slake value) was significantly lower in burned sites than unburned sites (median value=5 versus 6, P=0.008), a result which is likely due to the greater density of lichens and mosses encountered in the unburned plots. Soil microbe pigmentation was lower in burned plots (P=0.03), suggesting that the biomass of photosynthetic microbes had decreased; however, the presence of intra- and extracellular pigments in burned soils indicates that microorganisms were not eradicated. Pigments most strongly associated with cyanobacteria were more abundant in unburned sites, suggesting that cyanobacteria may have been more strongly impacted by the fire than other BSC components. Composition of nutrients and surface rugosity did not differ significantly between treatments. We hypothesize that Palouse prairie soil crusts are relatively resistant to wildfire because of low fire intensity and their occupation of space away from the vascular plant fuel load.

Applied Soil Ecology↗
USGS2024

Rethinking cost-share programs in consideration of economic equity: A case study of wildfire risk mitigation assistance for private landowners

Public agencies and organizations often deliver financial assistance through cost sharing, in which recipients contribute some portion toward total costs. However, cost sharing might raise equity concerns if it reduces participation among populations with lower incomes. Here, we revisit a past study using a richer dataset (n=1,689) to assess whether stated income levels affect survey respondents' willingness to participate in a cost share program for vegetation reduction to mitigate wildfire risk in western Colorado. Results show that residents with lower incomes are less likely to participate even though they can choose to contribute 0% toward a cost share. Residents reporting incomes less than $50,000 are 11 percentage points less likely to participate than those reporting incomes of $200,000 or more. They also are willing to pay a lower share (26 percentage points less) if they do participate. Results indicate potential economic equity concerns from the use of such programs.

Colorado↗
USGS2026

Valuing socio-economic and ecological attributes of forested watershed restoration to reduce wildfire risk in the southwestern U.S.

Forest restoration in a watershed can provide numerous ecological improvements and social benefits, including reducing the risk of extreme wildfire. Understanding the values of the accrued benefits can be used to evaluate the use of funds to support restoration. The Rio Grande watershed is a vast watershed covering approximately 335,000 mile 2 (867,646 km 2 ). The Rio Grande watershed provides a host of ecosystem services and recreation opportunities and supports municipal water supplies. We estimate the non-market values of forest restoration in the Rio Grande watershed using a choice experiment (CE) approach. While the ecological benefits are established in literature, we focus on the social characteristics, capturing the human-forest system in a comprehensive manner. Our results indicate a significant willingness to pay (WTP) for improving air quality, reducing private property damage, and creating local jobs, with the highest WTP for job creation. Split-sample analysis indicates respondents residing within the watershed highly value the socio-economic attributes of the restoration, while ecological attributes are preferred more outside of the watershed. Our results provide insights into the benefits of multi-dimensional services from forest restoration activities in a watershed.

New Mexico↗
USGS2009

'Natural background' soil water repellency in conifer forests of the north-western USA: Its prediction and relationship to wildfire occurrence

Soils under a wide range of vegetation types exhibit water repellency following the passage of a fire. This is viewed by many as one of the main causes for accelerated post-fire runoff and soil erosion and it has often been assumed that strong soil water repellency present after wildfire is fire-induced. However, high levels of repellency have also been reported under vegetation types not affected by fire, and the question arises to what degree the water repellency observed at burnt sites actually results from fire. This study aimed at determining 'natural background' water repellency in common coniferous forest types in the north-western USA. Mature or semi-mature coniferous forest sites (n = 81), which showed no evidence of recent fires and had at least some needle cast cover, were sampled across six states. After careful removal of litter and duff at each site, soil water repellency was examined in situ at the mineral soil surface using the Water Drop Penetration Time (WDPT) method for three sub-sites, followed by collecting near-surface mineral soil layer samples (0-3 cm depth). Following air-drying, samples were further analyzed for repellency using WDPT and contact angle (?? sl ) measurements. Amongst other variables examined were dominant tree type, ground vegetation, litter and duff layer depth, slope angle and aspect, elevation, geology, and soil texture, organic carbon content and pH. 'Natural background' water repellency (WDPT > 5 s) was detected in situ and on air-dry samples at 75% of all sites examined irrespective of dominant tree species (Pinus ponderosa, Pinus contorta, Picea engelmanii and Pseudotsuga menziesii). These findings demonstrate that the soil water repellency commonly observed in these forest types following burning is not necessarily the result of recent fire but can instead be a natural characteristic. The notion of a low background water repellency being typical for long-unburnt conifer forest soils of the north-western USA is therefore incorrect. It follows that, where pre-fire water repellency levels are not known or highly variable, post-fire soil water repellency conditions are an unreliable indicator in classifying soil burn severity. The terrain and soil variables examined showed, overall, no convincing relationship with the repellency levels observed (R 2 < 0.15) except that repellency was limited in soils (i) developed over meta-sedimentary lithology and (ii) with clay contents >4%. This suggests that water repellency levels cannot be predicted with confidence from common terrain or soil variables. ?? 2009 Elsevier B.V.

Journal of Hydrology↗