SmokePath Explorer is a web-based decision-support tool for California, U.S.A. that quantifies smoke transport probability and population exposure risk across the state, enabling data-driven strategies to minimize impacts while advancing fire management effectiveness. SmokePath integrates the California and Nevada Smoke and Air Committee (CANSAC) high-resolution (2-km) 20-year reanalysis climatology with HYSPLIT trajectory modeling. A total of 1.3 billion transport trajectories were precomputed with initializations four times per day at four distinct height levels capturing diurnal variations and injection height influences across various prescribed fire scenarios to support probabilistic smoke projections. Within the SmokePath online dashboard, users can input fire parameters and select specific months or weeks to assess smoke transport risk. The tool generates risk-level smoke transport contours from precomputed data and summarizes key meteorological variables. The system also provides population exposure estimates, including the total affected population, the number of smoke-sensitive facilities (i.e. educational and healthcare), and impacted USPS ZIP codes. User feedback has been key to developing SmokePath, enhancing usability, data integration, and decision-making for prescribed fire planning. To assess SmokePath's efficacy, we conducted case studies across diverse regions and validated results against independent observation datasets. These use cases assessed the accuracy of the WRF-CANSAC reanalysis dataset, which serves as the meteorological input for fire weather climatology and trajectory modeling. The fire case studies focused on identifying optimal burn windows and quantifying smoke transport patterns from (i) large multi-day prescribed fires, (ii) short duration (single-day) pile burns, and (iii) burns across diverse regions with complex topographic features. In most cases, modeled transport probability aligned with satellite-observed smoke plumes, capturing predominant dispersion patterns. Stakeholder feedback further supported the tool's practical utility - 85% indicated they would use SmokePath for prescribed fire planning, and 62% found it useful during wildfires.Implications: With catastrophic wildfires on the rise, California is expanding fuel treatments, including prescribed fire. While essential for mitigation, prescribed burns release smoke that can harm public health if unmanaged. SmokePath addresses this challenge by providing evidence-based insights on plume behavior to guide short- and long-term planning. The tool helps land managers schedule burns to minimize community impact, especially for vulnerable populations, and supports wildfire response with rapid smoke risk information. By improving public communication and enabling protective actions, SmokePath advances both health protection and the strategic use of prescribed fire.

The National Weather Service is responsible for alerting wildland fire management of meteorological conditions that create an environment conducive for extreme fire behavior. This is communicated via Red Flag Warnings (RFWs), which presently lack a national standardized methodology and rarely are explicitly linked to fuel conditions such those as provided by National Fire-Danger Rating System (NFDRS) indicators. The need for a revamped RFW has been expressed recently by both fire management and fire weather meteorologists. A decision matrix approach was developed to determine criteria that consistently and explicitly associates meteorological and fuels information to extreme fire behavior. Extreme fire behavior is defined here as maximum rates of spread (area per day) observed on documented large fires from 1999–2014 utilizing the ICS209 all-hazard dataset. Meteorological conditions occurring with these rates of spread were compared to historical percentiles of relative humidity, wind speed, and the NFDRS Energy Release Component. These percentiles were assigned a numerical score from one through five based on percentile rank. The additive result of all three scores was plotted against rates of spread yielding a two-step decision matrix of RFW categories where, for example, the highest score is the most extreme RFW case. Actual RFW issuances were compared to this matrix method.

Over the past four decades, annual area burned has increased significantly in California and across the western USA. This trend reflects a confluence of intersecting factors that affect wildfire regimes. It is correlated with increasing temperatures and atmospheric vapour pressure deficit. Anthropogenic climate change is the driver behind much of this change, in addition to influencing other climate-related factors, such as compression of the winter wet season. These climatic trends and associated increases in fire activity are projected to continue into the future. Additionally, factors related to the suppression of the Indigenous use of fire, aggressive fire suppression and, in some cases, changes in logging practices or fuel management intensity, collectively have produced large build-ups of vegetative fuels in some ecosystems. Human activities provide the most common ignition source for California's wildfires. Despite its human toll, fire provides a range of ecological benefits to many California ecosystems. Given the diversity of vegetation types and fire regimes found in the state, addressing California's wildfire challenges will require multi-faceted and locally targeted responses in terms of fuel management, human-caused ignitions, building regulations and restrictions, integrative urban and ecosystem planning, and collaboration with Tribes to support the reinvigoration of traditional burning regimes.

The spring and summer of 2019–2020 (Black Summer) saw the largest and most significant bushfire outbreak recorded in eastern Australia. In Victoria, the fires ran from mid-November through early autumn. In this paper, we use a high-spatial and temporal resolution 48-year fire weather re-analysis data set (VicClim5) to describe fire weather and vertical wind and stability profiles for five significant high Forest Fire Danger Index (FFDI) fire events and compare these with detailed fire reconstructions. A feature of several of these fires was very active overnight fire spread driven by topographically enhanced low-level jets and low fine fuel moisture content. The FFDI values on these nights were either the highest or near highest on record in the 48-year data set. We describe cases of lightning ignition, prefrontal fire spread and two cases of post-frontal fire spread – one into Mallacoota on the early morning of 31 December 2019 and the other a northward overnight run down the Buffalo Valley on 4–5 January 2020. On two of the days studied there were complex wind changes associated with the inland penetration of low-level south-easterly winds under the influence of locally generated pressure gradients. An elevated hot, dry mixed layer above these shallow layers also played an important role. On one occasion there is some evidence of possible mountain-wave modulation of surface wind flows. These events demonstrate a range of features of the fire weather and climate in eastern Victoria and the utility of VicClim5 in 3-dimensional climatological analyses.

It is well-documented that global nighttime temperatures have been increasing during the past few decades. For example, the average California nighttime temperature has increased at a rate of 0.7 °C per decade over the past 20 years. Temperature and atmospheric moisture (typically indicated by relative humidity in fire danger indices) are closely related, and dead fuel moisture (DFM) is a function of temperature and moisture via the equilibrium moisture content. Typically, as night temperature decreases, relative humidity increases, as does the DFM. Higher values of DFM is a factor in reducing fire behavior as the increased moisture reduces flammability. However, warmer nighttime temperatures and lower humidity allow fuel to stay drier, thus enabling fires to be more active throughout the night. Historically, fire management would often count on fires “laying down” at night as part of their tactical planning. However, an increasing number of incident reports across the western U.S have been highlighting active nocturnal fire behavior. This has consequences for firefighter safety and suppression success, impacting managed fire activities during the night, as well as the carryover into the next day. In this presentation, we examine the western U.S. trend in nighttime temperature in the context of nighttime fire behavior, discuss the potential fire management impact, and provide a global perspective.

Abstract Climate change uncertainty poses serious challenges to conservation efforts. One emerging conservation strategy is to identify and conserve climate change refugia: areas relatively buffered from contemporary climate change that enable persistence of valued resources. This management paradigm may be pursued at broad scales by leveraging existing resources and placing them into a tangible framework to stimulate further collaboration that fosters management decision‐making. Here, we describe a framework for moving toward operationalizing climate change refugia conservation at an ecoregion scale with an analysis for the Sierra Nevada ecoregion (CA, USA). Structured within the Climate Change Refugia Conservation Cycle, we identify a preliminary suite of conservation priorities for the ecoregion, and demonstrate how existing mapping, data, and applications could be used for identifying, prioritizing, managing, and monitoring refugia. We focus on six stakeholder‐identified conservation priorities, including two process‐based refugial priorities (snow and fire), and four ecosystem‐based refugial priorities (meadows, giant sequoia, old growth forests, and alpine communities). This pilot overview of concepts and resources provides a foundation for both near‐term implementation and further discussion in moving from science to conservation practice. Such an approach may provide new practical insights for ecosystem management at ecoregion scales in the face of climate change.

This paper applies the Multivariate Adaptive Constructed Analogs (MACA) statistical downscaling method to 12 general circulation models to produce 21st century projections of fire weather variables over Victoria, Australia, under two emissions scenarios. The statistically downscaled model data accurately replicate the observed distributions of meteorological variables over the contemporary period, but underestimate fire danger extremes in some models. Under each climate scenario, both mean and extreme fire danger are expected to increase. Though there is variation across Victoria, the 12-model average by year for RCP8.5 indicates a 10–20% increase in extreme (99th percentile) Forest Fire Danger Index across the state, with the greatest change projected in the north-west region. At five geographically and climatologically different locations across Victoria, there is a 50–200% increase in the number of days per year exceeding the threshold for the Victorian Very High or higher fire danger rating by the end of the century compared with the start. The high-end warming (RCP8.5) scenario shows increased temperature to be the main driver of heightened fire danger. Changes in temperature, humidity and precipitation during spring and early summer both increase the length of the fire season and may reduce springtime opportunities for prescribed burning.

Anthropogenic climate change is expected to cause an increase in fire danger over south-eastern Australia during the 21st century, primarily driven by increased surface temperature. Studies of future fire weather in Victoria, Australia, have so far mostly utilised direct output from general circulation models, which have inadequate resolution for resolving the dynamics of local fire danger and are prone to substantial biases that may affect the seasonality of dry fuels. In this paper, we assess the ability of the Multivariate Adaptive Constructed Analogs (MACA) method to downscale output from general circulation models over Victoria, and replicate statistical attributes of fire danger indices. We find that climatological descriptors of meteorological variables of wind, temperature and humidity are captured extremely well, and fields on extreme fire days are well captured. We find that the method works very well for statistically downscaling fire weather elements over Victoria and provides a vehicle to assess the regional variation of fire weather projections over Victoria.

Editors note: For easy download the posted pdf of the Explaining Extreme Events of 2018 is a very low-resolution file. A high-resolution copy of the report is available by clicking here . Please be patient as it may take a few minutes for the high-resolution file to download.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).CORRESPONDING AUTHOR: Timothy Brown, tim.brown@dri.edu

Abstract Successful restoration of California terrestrial ecosystems requires knowledge of seed germination rates for a diversity of native species. We quantified greenhouse germination of 25 native perennial forbs, shrubs, and grasses collected coastally near Santa Cruz, CA for restoration at the Younger Lagoon Reserve and nine annual forb species from interior grasslands at Pinnacles National Park. Seeds of most species were collected in multiple years. Twenty-seven of our 34 study species had at least 25% germination without complicated germination triggers. All but two of the 13 species that were collected in ≥3 years and germinated showed significant interannual variation in germination; seven species had a trend of decreasing percent germination with increasing age. These species- and collection-year specific results indicate a necessity to test seed stock when possible prior to seeding to increase restoration success, and highlight the importance of following best practices for seed collection and storage.

Wind changes are a critical factor in fire management, particularly on days of elevated fire danger, and have been shown to be a factor in many firefighter entrapments in Australia and the USA. While there have been numerous studies of frontal wind changes over southeastern Australia since the 1950s, a spatial climatology of wind change strength and frequency over Victoria has hitherto been limited by the relatively low number of observation sites that have both high temporal resolution observations and sufficient length of record. This study used a recently developed high spatial (4-km grid) and temporal (1hour) resolution, 46-year, homogeneous gridded fire weather climatology data set to generate a climatology of wind change strength by season at each gridpoint across Victoria. The metric used to define a wind change is the vector difference between the wind speed and direction over each 1-hour interval, with the highest value occuring on each day being selected for spatial analysis of strength and frequency. The highest values of wind change strength are found along the crest of the Great Dividing Range (the Great Divide), with a peak in spring. Elsewhere, the highest values occur in summer, with the areas south of the Great Divide, west of Melbourne and in central Gippsland showing higher values than the remainder of the state. The strength of wind changes generally decreases north of the Great Divide, although it is stronger in the northwest of the state in spring rather than in autumn. Lowest summertime (and other seasons) values occur in the northeast of the state and in far-east Gippsland. Exploring the frequencies of days when the highest daily Forest Fire Danger Index and the highest daily wind change strength jointly exceed defined thresholds shows that the northwest of the state has the highest springtime frequencies, whereas the highest autumn frequencies occur west of Melbourne and south of the Great Divide. The highest numbers of joint events in summer (when the greatest frequencies also occur) extend from central Victoria west to the South Australian border, with a secondary maximum in central Gippsland. These analyses offer important information for fire weather forecasters and for fire practitioners when preparing for a fire season or managing a fire campaign (for example, for allocating resources or understanding risks).

The Fire and Smoke Model Evaluation Experiment (FASMEE) is designed to collect integrated observations from large wildland fires and provide evaluation datasets for new models and operational systems. Wildland fire, smoke dispersion, and atmospheric chemistry models have become more sophisticated, and next-generation operational models will require evaluation datasets that are coordinated and comprehensive for their evaluation and advancement. Integrated measurements are required, including ground-based observations of fuels and fire behavior, estimates of fire-emitted heat and emissions fluxes, and observations of near-source micrometeorology, plume properties, smoke dispersion, and atmospheric chemistry. To address these requirements the FASMEE campaign design includes a study plan to guide the suite of required measurements in forested sites representative of many prescribed burning programs in the southeastern United States and increasingly common high-intensity fires in the western United States. Here we provide an overview of the proposed experiment and recommendations for key measurements. The FASMEE study provides a template for additional large-scale experimental campaigns to advance fire science and operational fire and smoke models.

There is an urgent need for next-generation smoke research and forecasting (SRF) systems to meet the challenges of the growing air quality, health and safety concerns associated with wildland fire emissions. This review paper presents simulations and experiments of hypothetical prescribed burns with a suite of selected fire behaviour and smoke models and identifies major issues for model improvement and the most critical observational needs. The results are used to understand the new and improved capability required for the next-generation SRF systems and to support the design of the Fire and Smoke Model Evaluation Experiment (FASMEE) and other field campaigns. The next-generation SRF systems should have more coupling of fire, smoke and atmospheric processes. The development of the coupling capability requires comprehensive and spatially and temporally integrated measurements across the various disciplines to characterise flame and energy structure (e.g. individual cells, vertical heat profile and the height of well-mixing flaming gases), smoke structure (vertical distributions and multiple subplumes), ambient air processes (smoke eddy, entrainment and radiative effects of smoke aerosols) and fire emissions (for different fuel types and combustion conditions from flaming to residual smouldering), as well as night-time processes (smoke drainage and super-fog formation).

Rainfall interception shelters are frequently used to study the ecological consequences of drought. One common shelter design employs V-shaped plastic troughs spaced on a supporting frame to intercept rainfall. Shading, reflection, and infrared radiation may alter the radiative environment under shelters in ways independent of their intended effect on soil moisture. We measured microclimate and several photosynthetic variables for watered, potted plants under rain-out shelters and in open-air, unsheltered plots. We tested whether the shelter infrastructure altered aboveground micrometeorology and photosynthesis for watered, potted plants of native Californian species: Elymus glaucus, Eriogonum latifolium, Mimulus aurantiacus, and Morella californica. We quantified the effects on photosynthesis in terms of light harvesting by photosystem II (PSII) and leaf-level gas exchange on open-air and shelter plots, the quantum yield of PSII for darkened leaves, dark respiration, and nocturnal stomatal conductance. The rain-out shelter reduced daily integrated photosynthetically active radiation by 20%. Air temperature, leaf temperature, and leaf-to-air vapour pressure difference were not different under shelters compared with controls during the day. Likewise, there were no effects of shelters on net CO2 assimilation, stomatal conductance to water vapour (g(s)), internal leaf (CO2), or electron transport rate through PSII during the daytime. At night, T-air was 0.6 degrees C higher under shelters, but there were no effects on dark respiration or stomatal conductance. Despite some differences in micrometeorology under rain-out shelters compared with open-air plots, there were little or no aboveground nondrought effects of the shelters on leaf-level photosynthesis for watered, potted plants of these California native plant species.

During the summer of 2015, a number of large wildfires burned across Northern California in areas of localized topographic relief. Persistent valley smoke hindered fire‐fighting efforts, delayed helicopter operations, and exposed communities to extreme concentrations of particulate matter. It was hypothesized that smoke from the wildfires reduced the amount of incoming solar radiation reaching the ground, which resulted in near‐surface cooling, while smoke aerosols resulted in warming aloft. As a result of increased inversion‐like conditions, smoke from wildfires was trapped within mountain valleys adjacent to active wildfires. In this study, wildfire smoke‐induced inversion episodes across Northern California were examined using a modeling framework that couples an atmospheric, chemical, and fire spread model. Modeling results examined in this study indicate that wildfire smoke reduced incoming solar radiation during the afternoon, which lead to local surface cooling by up to 3 °C, which agrees with cooling observed at nearby surface stations. Direct heating from the fire itself did not significantly enhance atmospheric stability. However, midlevel warming (+0.5 °C) and pronounced surface cooling was observed in the smoke layer, indicating that smoke aerosols significantly enhanced atmospheric stability. A positive feedback associated with the presence of smoke was observed, where local smoke‐enhanced inversions inhibited the growth of the planetary boundary layer, and reduced surface winds, which resulted in smoke accumulation that further reduced near‐surface temperatures. This work suggests that the inclusion of fire‐smoke‐atmosphere feedback in a coupled modeling framework such as WRF‐SFIRE‐CHEM can forecast the dispersion of wildfire smoke and its radiative feedback, and potentially provide decision‐support for wildfire operations.

During the summer of 2015, a number of wildfires fires burned across northern California, which produced significant smoke across the region. Smoke from these wildfires hindered fire-fighting efforts by delaying helicopter operations and exposed communities to high concentrations of atmospheric pollutants. Nighttime inversions are common across the western U.S. and usually mix out during the early afternoon as a result of convective mixing from daytime heating. However, atmospheric conditions in valleys adjacent to the aforementioned wildfires remained stable throughout the afternoon. It is hypothesized that the smoke from nearby wildfires enhanced atmospheric stability due to surface cooling caused by reduced incoming solar radiation, and possibly by warming aloft due to absorption of the incoming solar radiation in the smoke layer. At the same time, mid-level heating from the wildfire could have increased atmospheric stability and extended the duration of the inversion. In this study, we utilize the WRF-SFIRE-CHEM modeling framework, which couples an atmospheric, chemical, and fire spread model in an effort the model the impacts of smoke on local inversions and to improve the physical understanding behind these smoke-induced inversion episodes. This modeling framework was used to simulate the Route and South Complex fires between August 10 - August 26th, 2015. Preliminary results indicate that wildfire smoke may have significantly reduced incoming solar radiation, leading to local surface cooling by up to 2-3 degrees. Direct heating from the fire itself does not significantly enhance atmospheric stability. However, mid-level warming was observed in the smoke layer suggesting that absorption in this layer may have enhanced the inversion. This study suggests the including the fire-smoke atmosphere feedbacks in a coupled modeling framework such as WRF-SFIRE-CHEM may help in capturing the impacts of wildfire smoke on near-surface stability and local inversions.

Most of the life and property losses due to bushfires in south-eastern Australia occur under extreme fire weather conditions – strong winds, high temperatures, low relative humidity (RH) and extended drought. However, what constitutes extreme, and the values of the weather ingredients and their variability, differs regionally. Using a gridded dataset to identify the highest 10 fire weather days from 1972 to 2012, as defined by McArthur’s Forest Fire Danger Index (FFDI), for 24 sites across Victoria and nearby, we analyse the extent and variability of these highest 10 FFDI days, and of the contributing temperature, RH, wind speed, wind direction and drought indices. We document the occurrence of these events by time of day, month of occurrence and inter-annual variability. We find there is considerable variability among regions in the highest FFDI days and also the contributing weather and drought parameters, with some regional groupings apparent. Many major fire events occurred on these highest 10 fire weather days; however there are also days in which extreme fire weather occurred yet no known major fires are recorded. The results from this study will be an additional valuable resource to fire agencies in fire risk planning by basing fire management decisions on site-specific extreme fire weather conditions.

Climatology data of fire weather across the landscape can provide science-based evidence for informing strategic decisions to ameliorate the impacts (at times extreme) of bushfires on community socio-economic wellbeing and to sustain ecosystem health and functions. A long-term climatology requires spatial and temporal data that are consistent to represent the landscape in sufficient detail to be useful for fire weather studies and management purposes. To address this inhomogeneity problem for analyses of a variety of fire weather interests and to provide a dataset for management decision-support, a homogeneous 41-year (1972-2012), hourly interval, 4 km gridded climate dataset for Victoria has been generated using a combination of mesoscale modelling, global reanalysis data, surface observations, and historic observed rainfall analyses. Hourly near-surface forecast fields were combined with Drought Factor (DF) fields calculated from the Australian Water Availability Project (AWAP) rainfall analyses to generate fields of hourly fire danger indices for each hour of the 41-year period. A quantile mapping (QM) bias correction technique utilizing available observations during 1996-2012 was used to ameliorate any model biases in wind speed, temperature and relative humidity. Extensive evaluation was undertaken including both quantitative and case study qualitative assessments. The final dataset includes 4-km surface hourly temperature, relative humidity, wind speed, wind direction, Forest Fire Danger Index (FFDI), and daily DF and Keetch-Byram Drought Index (KBDI), and a 32-level full three-dimensional volume atmosphere.

Restoration in Mediterranean-climate grasslands is strongly impeded by lack of native propagules and competition with exotic grasses and forbs. We report on a study testing several methods for exotic plant control combined with planting native grasses to restore prairies in former agricultural land in coastal California. Specifically we compared tarping (shading out recently germinated seedlings with black plastic) once, tarping twice, topsoil removal, herbicide (glyphosate), and a control treatment in factorial combinations with or without wood mulch. Into each treatment we planted three native grass species (Elymus glaucus, Hordeum brachyantherum, and Stipa pulchra) and monitored plant survival and cover for three growing seasons. Survival of native grass species was high in all treatments, but was slightly lower in unmulched soil removal and control treatments in the first 2 yr. Mulching, tarping, and herbicide were all effective in reducing exotic grass cover and enhancing native grass cover for the first 2 yr, but by the third growing season cover of the plant guilds and bare ground had mostly converged, primarily because of the declining effects of the initial treatments. Mulching and tarping were both considerably more expensive than herbicide treatment. Topsoil removal was less effective in increasing native grass cover likely because soil removal altered the surface hydrology in this system. Our results show that several treatments were effective in enhancing native grass establishment, but that longer term monitoring is needed to evaluate the efficacy of restoration efforts. The most appropriate approach to controlling exotics to restore specific grassland sites will depend not only on the effectiveness, but also on relative costs and site constraints.