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At least 235 records · Page 13Linked to original sources
USGS2023

Assessment of post-wildfire geomorphic change in the North Fork Eagle Creek stream channel, New Mexico, 2017–21

The 2012 Little Bear Fire caused substantial vegetation loss in the Eagle Creek Basin of south-central New Mexico. This loss was expected to alter the localized hydrologic response to precipitation by creating conditions that amplify surface runoff, which might alter the geomorphology of North Fork Eagle Creek, a major tributary to Eagle Creek. To monitor short-term geomorphic change, annual geomorphic surveys of North Fork Eagle Creek were conducted from 2017 to 2021. The surveys measured 14 cross sections, stream gradients, woody debris accumulations, and pools found within the study reach. During the 2017–21 study period, the study reach experienced multiple high-flow events that resulted from both monsoonal rainfall and snowmelt runoff. Comparisons of the cross-section and channel profile data for the repeat geomorphic surveys indicate localized erosion and deposition occurred as a result of the high-flow events but overall study reach geomorphology shower little change through the study period. Additionally, the number of woody debris accumulations and pools increased during the study period. Evidence from the 5-year geomorphic survey indicates that the North Fork Eagle Creek’s geomorphology did not change substantially during the study period. Wildfire severity and frequency within mountainous regions of the Southwest are projected to increase and their effect on fluvial systems remains uncertain; however, continued geomorphic studies can provide informative insight on watershed post-wildfire resiliency and recovery by establishing baselines that can be used in the event of a future severe wildfire within the Eagle Creek Basin.

New Mexico↗
USGS2018

Modeling wildfire-induced permafrost deformation in an Alaskan boreal forest using InSAR observations

The discontinuous permafrost zone is one of the world’s most sensitive areas to climate change. Alaskan boreal forest is underlain by discontinuous permafrost, and wildfires are one of the most influential agents negatively impacting the condition of permafrost in the arctic region. Using interferometric synthetic aperture radar (InSAR) of Advanced Land Observation Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) images, we mapped extensive permafrost degradation over interior Alaskan boreal forest in Yukon Flats, induced by the 2009 Big Creek wildfire. Our analyses showed that fire-induced permafrost degradation in the second post-fire thawing season contributed up to 20 cm of ground surface subsidence. We generated post-fire deformation time series and introduced a model that exploited the deformation time series to estimate fire-induced permafrost degradation and changes in active layer thickness. The model showed a wildfire-induced increase of up to 80 cm in active layer thickness in the second post-fire year due to pore-ice permafrost thawing. The model also showed up to 15 cm of permafrost degradation due to excess-ice thawing with little or no increase in active layer thickness. The uncertainties of the estimated change in active layer thickness and the thickness of thawed excess ice permafrost are 27.77 and 1.50 cm, respectively. Our results demonstrate that InSAR-derived deformation measurements along with physics models are capable of quantifying fire-induced permafrost degradation in Alaskan boreal forests underlain by discontinuous permafrost. Our results also have illustrated that fire-induced increase of active layer thickness and excess ice thawing contributed to ground surface subsidence.

Alaska↗
USGS2011

Wildfires alter rodent community structure across four vegetation types in southern California, USA

We surveyed burned and unburned plots across four habitat reserves in San Diego County, California, USA, in 2005 and 2006, to assess the effects of the 2003 wildfires on the community structure and relative abundance of rodent species. The reserves each contained multiple vegetation types (coastal sage scrub, chaparral, woodland, and grassland) and spanned from 250 m to 1078 m in elevation. Multivariate analyses revealed a more simplified rodent community structure in all burned habitats in comparison to unburned habitats. Reduction in shrub and tree cover was highly predictive of changes in post-fire rodent community structure in the burned coastal sage scrub and chaparral habitats. Reduction in cover was not predictive for the less substantially burned woodlands and grasslands, for which we hypothesized that interspecific competition played a greater role in post-fire community structure. Across vegetation types, generalists and open habitat specialists typically increased in relative abundance, whereas closed habitat specialists decreased. We documented significant increases in relative abundance of the deer mouse ( Peromyscus maniculatus Wagner) and Dulzura kangaroo rat ( Dipodomys simulans Merriam). In contrast, we found significant decreases in relative abundance for the California mouse ( Peromyscus californicus Gambel), San Diego pocket mouse ( Chaetodipus fallax Merriam), desert woodrat ( Neotoma lepida Thomas), and brush mouse ( Peromyscus boylii Baird). Currently, our research program involves assessment of whether habitat conservation plans (HCPs) in southern California provide long-term protection to HCP covered species, as well as preserve ecosystem function. The scenario of increased wildfires needs to be incorporated into this assessment. We discuss our results in relation to management and conservation planning under a future scenario of larger and more frequent wildfires in southern California.

California↗
USGS2009

The 2007 southern California wildfires: Lessons in complexity

The 2007 wildfire season in southern California burned over 1,000,000 ac (∼400,000 ha) and included several megafires. We use the 2007 fires as a case study to draw three major lessons about wildfires and wildfire complexity in southern California. First, the great majority of large fires in southern California occur in the autumn under the influence of Santa Ana windstorms. These fires also cost the most to contain and cause the most damage to life and property, and the October 2007 fires were no exception because thousands of homes were lost and seven people were killed. Being pushed by wind gusts over 100 kph, young fuels presented little barrier to their spread as the 2007 fires reburned considerable portions of the area burned in the historic 2003 fire season. Adding to the size of these fires was the historic 2006‐2007 drought that contributed to high dead fuel loads and long distance spotting. As in 2003, young chaparral stands and fuel treatments were not reliable barriers to fire in October 2007. Second, the Zaca Fire in July and August 2007 showed that other factors besides high winds can sometimes combine to create conditions for large fires in southern California. Spring and summer fires in southern California chaparral are usually easily contained because of higher fuel moisture and the general lack of high winds. However, the Zaca Fire burned in a remote wilderness area of rugged terrain that made access difficult. In addition, because of its remoteness, anthropogenic ignitions have been low and stand age and fuel loads were high. Coupled with this was severe drought that year that generated fuel moisture levels considerably below normal for early summer. A third lesson comes from 2007 conifer forest fires in the southern California mountains. In contrast to lower elevation chaparral, fire suppression has led to major increases in conifer forest fuels that can lead to unnaturally severe fires when ignitions escape control. The Slide and Grass Valley Fires of October 2007 occurred in forests that had been subject to extensive fuel treatment, but fire control was complicated by a patchwork of untreated private properties and mountain homes built of highly flammable materials. In a fashion reminiscent of other recent destructive conifer fires in California, burning homes themselves were a major source of fire spread. These lessons suggest that the most important advances in fire safety in this region are to come from advances in fire prevention, fire preparedness, and land-use planning that includes fire hazard patterns.

California↗
USGS2012

Effects of wildfire on source-water quality and aquatic ecosystems, Colorado Front Range

Watershed erosion can dramatically increase after wildfire, but limited research has evaluated the corresponding influence on source-water quality. This study evaluated the effects of the Fourmile Canyon wildfire (Colorado Front Range, USA) on source-water quality and aquatic ecosystems using high- frequency sampling. Dissolved organic carbon (DOC) and nutrient loads in stream water were evaluated for a one-year period during different types of runoff events, including spring snowmelt, and both frontal and summer convective storms. DOC export from the burned watershed did not increase relative to the unburned watershed during spring snowmelt, but substantial increases in DOC export were observed during summer convective storms. Elevated nutrient export from the burned watershed was observed during spring snowmelt and summer convective storms, which increased the primary productivity of stream biofilms. Wildfire effects on source-water quality were shown to be substantial following high-intensity storms, with the potential to affect drinking-water treatment processes.

Colorado↗
USGS2017

Climate, wildfire, and erosion ensemble foretells more sediment in western USA watersheds

The area burned annually by wildfires is expected to increase worldwide due to climate change. Burned areas increase soil erosion rates within watersheds, which can increase sedimentation in downstream rivers and reservoirs. However, which watersheds will be impacted by future wildfires is largely unknown. Using an ensemble of climate, fire, and erosion models, we show that post-fire sedimentation is projected to increase for nearly nine-tenths of watersheds by > 10% and for more than one-third of watersheds by > 100% by the 2041 to 2050 decade in the western USA. The projected increases are statistically significant for more than eight-tenths of the watersheds. In the western USA, many human communities rely on water from rivers and reservoirs that originates in watersheds where sedimentation is projected to increase. Increased sedimentation could negatively impact water supply and quality for some communities, in addition to affecting stream channel stability and aquatic ecosystems.

Geophysical Research Letters↗
USGS2021

Acute and lagged fitness consequences for a sagebrush obligate in a post mega-wildfire landscape

Species responses to disturbance influence their extinction risks. Greater sage- grouse ( Centrocercus urophasianus ) are bioindicators of sagebrush ecosystem health and the loss of sagebrush ( Artemisia spp.) due to wildfire, can cause long- term declines in sage- grouse populations and other sagebrush obligate species. We examined the de - mographic response of a greater sage- grouse population following a mega- wildfire using stochastic age- structured female- based matrix models over 6 years (2013– 2018). Notably, chick survival (range = 0.18– 0.38) and female survival (yearling range: 0.20– 0.68; adult range: 0.27– 0.75) were low compared to values reported for greater sage- grouse in other parts of their distribution. Greater sage- grouse displayed vari - ation in demographic tactics after the fire; however, adult female survival explained most of the variation in λ during each year, which reflected a declining population in 3 of 6 years with more uncertainty observed in 2015 when populations may have been increasing, and 2017 and 2018, when populations may have been declining. The continued annual population decline observed since 2016 suggested there were ad - ditional strong environmental impacts that may have been compounded by the fire effects, prolonging recovery of greater sage- grouse. Our results support others that reported negative effects to greater sage- grouse demographics from broad- scale fire and provide a baseline for understanding how this species responds to loss of sage - brush cover based on their life history strategy.

Nevada, Oregon↗
USGS2022

Temporal mismatch in space use by a sagebrush obligate species after large-scale wildfire

The increase in size and frequency of wildfires in sagebrush steppe ecosystems has significant impacts on sagebrush obligate species. We modeled seasonal habitat use by female greater sage-grouse ( Centrocercus urophasianus ) in the Trout Creek Mountains of Oregon and Nevada, USA, to identify landscape characteristics that influenced sage-grouse habitat selection and to create predictive surfaces of seasonal use 1 and 7 years postfire. We developed three resource selection function models using GPS location data from 2013 to 2019 for three biologically distinct seasons (breeding, n = 149 individuals: 8 March–12 June; summer, n = 140 individuals: 13 June–20 October; and winter, n = 94 individuals: 21 October–7 March). For all seasons, by the fourth or fifth year postfire, sage-grouse selected for unburned patches more than all other burn severity patches and the use of unburned areas in comparison with burned areas increased through time. During the breeding season, sage-grouse selected for low-sagebrush ( Artemisia arbuscula )-dominated ecosystems and areas with low biomass (normalized difference vegetation index). During summer, sage-grouse selected for areas with higher annual and perennial grasses and forb cover, and areas that had higher biomass. During winter, sage-grouse selected for areas of intact sagebrush on less rugged terrain. For the winter and breeding season, there was a positive linear relationship between annual grasses and forb cover through time. Seven years postfire (2019), the area predicted to have a high probability of use in each seasonal range decreased (breeding: 16.4%; summer: 12.2%; and winter: 4.2%), while the area predicted to have low or low-medium probability of use increased (breeding: 14.5%; summer: 22.5%; and winter: 22.8%) when compared to the first year following the wildfire (2013). Our results demonstrated a 4- to 5-year time lag before female sage-grouse adapted to a disturbed landscape began avoiding burned areas more than intact, unburned habitats. This mismatch in ecological response may imply declines in habitat availability for sage-grouse and may destabilize population vital rates. Spatially explicit models can aid in identifying priority areas for restoration efforts and conservation actions to mitigate the impacts of future disturbances.

Nevada, Oregon↗
USGS2022

Reestablishing a foundational species: limitations on post-wildfire sagebrush seedling establishment

Improving post-wildfire restoration of foundational plant species is crucial for conserving imperiled ecosystems. We sought to better understand the initial establishment of sagebrush ( Artemisia sp.), a foundational shrubland species over a vast area of western North America, in the first 1–2 years post-wildfire, a critical time period for population recovery. Field data from 460 sagebrush populations sampled across the Great Basin revealed several patterns. Sagebrush seedlings were uncommon in the first 1–2 years after fire, with none detected in 69% of plots, largely because most fires occurred in areas of low resistance to invasive species and resilience to disturbance (hereafter, R&R). Post-fire aerial seeding of sagebrush dramatically increased seedling occupancy, especially in low R&R areas, which exhibited a 3.4-fold increase in occupancy over similar unseeded locations. However, occupancy models and repeat surveys suggested exceptionally high mortality, as occupancy rates declined by as much as 50% between the first and second years after fire. We found the prevalence of “fertile island” microsites (patches beneath fire-consumed sagebrush) to be the best predictor of seedling occupancy, followed by aerial seeding status, native perennial grass cover, and years since fire. In populations where no sagebrush seeding occurred, seedlings were most likely to occur in locations with a combination of high fertile island microsite cover and close proximity to a remnant sagebrush plant. These important attributes were only present in 13% of post-fire locations, making them rare across the Great Basin. Finally, in the absence of fertile islands and remnant plants, seedling establishment was not observed in any unseeded areas, and rarely in seeded locations. Thus, local extirpation of sagebrush could have important, long-term implications for sagebrush reestablishment following future fires if there are no mature individuals to leave behind fertile islands or serve as remnant individuals. These findings highlight the importance of landscape legacy effects and could help guide where and how big sagebrush restoration is conducted in the future.

California, Idaho, Nevada, Oregon, Utah↗
USGS2023

Long-term relationships between seed bank communities and wildfire across four North American desert sites

It is well documented that the recovery of dryland plant communities following wildfire can be variable, and that legacies of fire can have long-lasting effects on aboveground plant communities. However, our understanding of the degree to which dryland soil seed banks, or the viable seeds in situ, are impacted by fire and their subsequent postfire succession remains extremely poor. To address this important knowledge gap, we used a time-since-fire approach to investigate soil seed bank community changes approximately 15 and 30 years after wildfire and to determine the influence of microsites (e.g., shrub vs. interspace) on seed bank composition. We assessed soil seed bank metrics across four North American deserts, including two cold desert sites (Colorado Plateau and Great Basin) and two warm desert sites (Chihuahuan and Sonoran). In greenhouse emergence trials, we found that seed bank characteristics diverged between warm and cold desert sites, such that warm desert sites had seed banks dominated by annual plants while our cold desert sites had seed banks with greater proportions of perennial species, regardless of fire history. In cold desert sites, fire significantly altered seed bank species composition even 30 years after fire. Shrub versus interspace microsites had no observed influence on seed bank composition in any desert. However, seed bank species richness was greater under shrubs in both warm deserts. Non-native species were present in the seed banks of all deserts and some were particularly abundant in the burned sites. Despite the presence of native species in both burned and unburned seed banks, the presence of non-native species suggests some degree of vulnerability to future disturbances because fire can create amplifying feedback with many non-native plants. Our results highlight strong differences in fires' relationship with seed banks for warm and cold desert sites and lend insight into how fire relates to the composition and diversity of the seeds that play a fundamental role in future plant communities.

Arizona, Colorado, Nevada, New Mexico↗
USGS2015

Measurements of the initiation of post-wildfire runoff during rainstorms using in situ overland flow detectors

Overland flow detectors (OFDs) were deployed in 2012 on a hillslope burned by the 2010 Fourmile Canyon fire near Boulder, Colorado, USA. These detectors were simple, electrical resistor-type instruments that output a voltage (0–2·5 V) and were designed to measure and record the time of runoff initiation, a signal proportional to water depth, and the runoff hydrograph during natural convective rainstorms. Initiation of runoff was found to be spatially complex and began at different times in different locations on the hillslope. Runoff started first at upstream detectors 56% of the time, at the mid-stream detectors 6%, and at the downstream detectors 38% of the time. Initiation of post-wildfire runoff depended on the time-to-ponding, travel time between points, and the time to fill surface depression storage. These times ranged from 0·5–54, 0·4–1·1, and 0·2–14 minutes, respectively, indicating the importance of the ponding process in controlling the initiation of runoff at this site. Time-to-ponding was modeled as a function of the rainfall acceleration (i.e. the rate of change of rainfall intensity) and either the cumulative rainfall at the start of runoff or the soil–water deficit. Measurements made by the OFDs provided physical insight into the spatial and temporal initiation of post-wildfire runoff during unsteady flow in response to time varying natural rainfall. They also provided data that can be telemetered and used to determine critical input parameters for hydrologic rainfall–runoff models.

Earth Surface Processes and Landforms↗
USGS2019

The ecological uncertainty of wildfire fuel breaks: Examples from the sagebrush steppe

Fuel breaks are increasingly being implemented at broad scales (100s to 10,000s of square kilometers) in fire‐prone landscapes globally, yet there is little scientific information available regarding their ecological effects (eg habitat fragmentation). Fuel breaks are designed to reduce flammable vegetation (ie fuels), increase the safety and effectiveness of fire‐suppression operations, and ultimately decrease the extent of wildfire spread. In sagebrush ( Artemisia spp) ecosystems of the western US, installation of extensive linear fuel breaks is also intended to protect habitat, especially for the greater sage‐grouse ( Centrocercus urophasianus ), a species that is sensitive to habitat fragmentation. We examine this apparent contradiction in the Great Basin region, where invasive annual grasses have increased wildfire activity and threaten sagebrush ecosystems. Given uncertain outcomes, we examine how implementation of fuel breaks might (1) directly alter ecosystems, (2) create edges and edge effects, (3) serve as vectors for wildlife movement and plant invasions, (4) fragment otherwise contiguous sagebrush landscapes, and (5) benefit from scientific investigation intended to disentangle their ecological costs and benefits.

California, Idaho, Nevada, Oregon, Utah↗
USGS2021

Wildfires and global change

No single factor produces wildfires; rather, they occur when fire thresholds (ignitions, fuels, and drought) are crossed. Anomalous weather events may lower these thresholds and thereby enhance the likelihood and spread of wildfires. Climate change increases the frequency with which some of these thresholds are crossed, extending the duration of the fire season and increasing the frequency of dry years. However, climate-related factors do not explain all of the complexity of global fire-regime changes, as altered ignition patterns (eg human behavior) and fuel structures (eg land-use changes, fire suppression, drought-induced dieback, fragmentation) are extremely important. When the thresholds are crossed, the size of a fire will largely depend on the duration of the fire weather and the extent of the available area with continuous fuels in the landscape.

southeast Australia↗
USGS2015

Water-quality response to a high-elevation wildfire in the Colorado Front Range

Water quality of the Big Thompson River in the Front Range of Colorado was studied for 2 years following a high‐elevation wildfire that started in October 2012 and burned 15% of the watershed. A combination of fixed‐interval sampling and continuous water‐quality monitors was used to examine the timing and magnitude of water‐quality changes caused by the wildfire. Prefire water quality was well characterized because the site has been monitored at least monthly since the early 2000s. Major ions and nitrate showed the largest changes in concentrations; major ion increases were greatest in the first postfire snowmelt period, but nitrate increases were greatest in the second snowmelt period. The delay in nitrate release until the second snowmelt season likely reflected a combination of factors including fire timing, hydrologic regime, and rates of nitrogen transformations. Despite the small size of the fire, annual yields of dissolved constituents from the watershed increased 20–52% in the first 2 years following the fire. Turbidity data from the continuous sensor indicated high‐intensity summer rain storms had a much greater effect on sediment transport compared to snowmelt. High‐frequency sensor data also revealed that weekly sampling missed the concentration peak during snowmelt and short‐duration spikes during rain events, underscoring the challenge of characterizing postfire water‐quality response with fixed‐interval sampling.

Colorado↗
USGS2016

Synthesis of soil-hydraulic properties and infiltration timescales in wildfire-affected soils

We collected soil-hydraulic property data from the literature for wildfire-affected soils, ash, and unburned soils. These data were used to calculate metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity ( S ) and wetting front potential (Ψ f ) were significantly different (lower) in burned soils compared with unburned soils, whereas field-saturated hydraulic conductivity ( K fs ) was not significantly different. The magnitude and duration of the influence of capillarity during infiltration was greatly reduced in burned soils, causing faster ponding times in response to rainfall. Ash had large values of S and K fs but moderate values of Ψ f , compared with unburned and burned soils, indicating ash has long ponding times in response to rainfall. The ratio of S 2 /K fs was nearly constant (~100 mm) for unburned soils but more variable in burned soils, suggesting that unburned soils have a balance between gravity and capillarity contributions to infiltration that may depend on soil organic matter, whereas in burned soils the gravity contribution to infiltration is greater. Changes in S and K fs in burned soils act synergistically to reduce infiltration and accelerate and amplify surface runoff generation. Synthesis of these findings identifies three key areas for future research. First, short timescales of capillary influences on infiltration indicate the need for better measurements of infiltration at times less than 1 min to accurately characterize S in burned soils. Second, using parameter values, such as Ψ f , from unburned areas could produce substantial errors in hydrologic modeling when used without adjustment for wildfire effects, causing parameter compensation and resulting underestimation of K fs . Third, more thorough measurement campaigns that capture soil-structural changes, organic matter impacts, quantitative water repellency trends, and soil-water content along with soil-hydraulic properties could drive the development of better techniques for numerically simulating infiltration in burned areas.

Hydrological Processes↗
USGS2013

Limiting the immediate and subsequent hazards associated with wildfires

Wildfire is a unique natural hazard because it poses immediate threats to life and property as well as creating conditions that can lead to subsequent debris flows. In recent years, the immediate destructive force of wildfires has been decreased through better understanding of fire behavior. Lightning detection networks now identify the number and locations of this common ignition source. Measurements of wind speed, temperature, slope, fuel types and fire boundaries are routinely incorporated into models for fire spread, permitting real-time adjustments to fire-fighting strategies, thus increasing fire-fighting effectiveness. Similarly, our capability to limit impacts from post-fire debris flows is improving. Empirical models for estimating the probability of debris-flow occurrence, the volume of such an event, and mapping the inundated area, linked with improved definitions of the rainfall conditions that trigger debris flows, can be used to provide critical information for post-fire hazard mitigation and emergency-response planning.

Book chapter↗
USGS1998

Water quality of two streams near Yellowstone Park, Wyoming, following the 1988 Clover-Mist wildfire

In 1988, wildfire burned over 50% of the Jones Creek watershed near Yellowstone Park, Wyoming. Crow Creek, an adjacent watershed, was unburned. Water quality data collected from 1989-1993 may show the fire's effect on weathering and nutrient transport. Jones Creek had 25-75% larger concentration of dissolved solids than Crow Creek during the sampling period. Both streams revealed molar ratios consistent with the stoichiometry of andesine and pyroxene hydrolysis in the trachyandesites that underlie the basins. During 1989, nitrate transported from the unburned Crow Creek basin peaked at 2 mmol ha-1 s-1. This was twice as much as Jones Creek, possibly indicating a source from ash fallout. By 1992 these rates diminished to 0.1 mmol ha-1 s-1 in Crow Creek and increased to 1.8 mmol ha-1 s-1 in Jones Creek, suggesting later nitrate mobilization in the burned watershed. Phosphorus transported from Jones Creek basin averaged 0.011 mmol ha-1 s-1 during summer 1989, but fell to 0.004 mg ha-1 s-1 in subsequent years.In 1988, wildfire burned over 50% of the Jones Creek watershed near Yellowstone Park, Wyoming. Crow Creek, an adjacent watershed, was unburned. Water quality data collected from 1989-1993 may show the fire's effect on weathering and nutrient transport. Jones Creek had 25-75% larger concentrations of dissolved solids than Crow Creek during the sampling period. Both streams revealed molar ratios consistent with the stoichiometry of andesine and pyroxene hydrolysis in the trachyandesites that underlie the basins. During 1989, nitrate transported from the unburned Crow Creek basin peaked at 2 mmol ha-1 s-1. This was twice as much as Jones Creek, possibly indicating a source from ash fallout. By 1992 these rates diminished to 0.1 mmol ha-1 s-1 in Crow Creek and increased to 1.8 mmol ha-1 s-1 in Jones Creek, suggesting later nitrate mobilization in the burned watershed. Phosphorus transported from Jones Creek basin averaged 0.011 mmol ha-1 s-1 during summer 1989, but fell to 0.004 mg ha-1 s-1 in subsequent years.

Environmental Geology↗
USGS2017

Drought, multi-seasonal climate, and wildfire in northern New Mexico

Wildfire is increasingly a concern in the USA, where 10 million acres burned in 2015. Climate is a primary driver of wildfire, and understanding fire-climate relationships is crucial for informing fire management and modeling the effects of climate change on fire. In the southwestern USA, fire-climate relationships have been informed by tree-ring data that extend centuries prior to the onset of fire exclusion in the late 1800s. Variability in cool-season precipitation has been linked to fire occurrence, but the effects of the summer North American monsoon on fire are less understood, as are the effects of climate on fire seasonality. We use a new set of reconstructions for cool-season (October–April) and monsoon-season (July–August) moisture conditions along with a large new fire scar dataset to examine relationships between multi-seasonal climate variability, fire extent, and fire seasonality in the Jemez Mountains, New Mexico (1599–1899 CE). Results suggest that large fires burning in all seasons are strongly influenced by the current year cool-season moisture, but fires burning mid-summer to fall are also influenced by monsoon moisture. Wet conditions several years prior to the fire year during the cool season, and to a lesser extent during the monsoon season, are also important for spring through late-summer fires. Persistent cool-season drought longer than 3 years may inhibit fires due to the lack of moisture to replenish surface fuels. This suggests that fuels may become increasingly limiting for fire occurrence in semi-arid regions that are projected to become drier with climate change.

New Mexico↗