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Rim Fire map, with color scheme indicating the USFS estimated daily fire progression based on the NIROPS observation closest to local midnight for 17 August to 22 September 2013. Solid blue and dashed black arrows indicate the approximate area burned during spread event #1 and spread event #2, respectively.
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The 2013 Rim Fire, which burned over 104,000 ha, was one of the most severe fire events in California’s history, in terms of its rapid growth, intensity, overall size, and persistent smoke plume. At least two large pyrocumulonimbus (pyroCb) events were observed, allowing smoke particles to extend through the upper troposphere over a large portion o...
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... conditions. The intense burning and rapid spread observed during the primary burning period of 17-31 August generally coincided with warm temperatures and relative humidity (RH) values below 40% each afternoon. However, several key changes in local meteorology were also observed. During the first few days of the fire, a large portion of California was under the influence of a broad upper-level low that became cutoff from the mean synoptic flow in the days preceding ignition (Fig. 3a). The North American Regional Reanalysis (NARR; #narr_datasets; Mesinger et al. 2006) shows that the center of the low was located off the southern California coastline on the first day of burning (18 August), and low-level winds (850 hPa) were light and southeasterly near the Rim Fire. As is typical with large cutoffs, the low then began to retrograde (e.g., Holton 2004), causing low-level winds near the fire to shift more northerly by the evening of 19 August (Fig. 4a). This directed the fire front to the south, or generally downhill (Fig. 1). During 20 - 22 August, the low progressed back toward California, causing low-level winds to become southwesterly (Fig. 4b- d), redirecting the fire to the northeast along generally uphill slopes (Fig. 1). As near-surface pressure gradients increased between the low and an inland ridge, wind speeds increased from 5 kt (3 m·s ) to 15-20 kt (8-10 m·s ). This combination of stronger winds in a general uphill and up-canyon direction very likely increased the rate of fire spread. Relatively cold upper-tropospheric air associated with the cutoff low provided sufficient instability for scattered convection and some precipitation in the higher terrain near the fire. The two pyroCb events also occurred during this period, on 19 and 21 August. Convective activity then diminished as the cutoff low merged with a broad synoptic trough approaching the Pacific Northwest. Southwesterly synoptic flow on the eastern side of the trough pushed the ...
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... conditions. The intense burning and rapid spread observed during the primary burning period of 17-31 August generally coincided with warm temperatures and relative humidity (RH) values below 40% each afternoon. However, several key changes in local meteorology were also observed. During the first few days of the fire, a large portion of California was under the influence of a broad upper-level low that became cutoff from the mean synoptic flow in the days preceding ignition (Fig. 3a). The North American Regional Reanalysis (NARR; #narr_datasets; Mesinger et al. 2006) shows that the center of the low was located off the southern California coastline on the first day of burning (18 August), and low-level winds (850 hPa) were light and southeasterly near the Rim Fire. As is typical with large cutoffs, the low then began to retrograde (e.g., Holton 2004), causing low-level winds near the fire to shift more northerly by the evening of 19 August (Fig. 4a). This directed the fire front to the south, or generally downhill (Fig. 1). During 20 - 22 August, the low progressed back toward California, causing low-level winds to become southwesterly (Fig. 4b- d), redirecting the fire to the northeast along generally uphill slopes (Fig. 1). As near-surface pressure gradients increased between the low and an inland ridge, wind speeds increased from 5 kt (3 m·s ) to 15-20 kt (8-10 m·s ). This combination of stronger winds in a general uphill and up-canyon direction very likely increased the rate of fire spread. Relatively cold upper-tropospheric air associated with the cutoff low provided sufficient instability for scattered convection and some precipitation in the higher terrain near the fire. The two pyroCb events also occurred during this period, on 19 and 21 August. Convective activity then diminished as the cutoff low merged with a broad synoptic trough approaching the Pacific Northwest. Southwesterly synoptic flow on the eastern side of the trough pushed the ...
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... and ejected it through central California between 21 and 22 August (Fig. 3a). The digging trough also maintained a strong pressure gradient over central California, producing strong surface winds (Fig. 4d). This coincides with the rapid uphill fire spread observed during spread event #1 (Fig. 1), marked by the largest increases in both area burned and FRP (Fig. 2). During 24 August and part of 25 August, the Rim Fire’s growth slowed and FRP decreased (Figs. 1, 2). This was largely influenced by increasing RH, reduced wind speed, and the lowest surface temperatures observed during the primary burning period. While the air temperature was lower, the passage of a shortwave trough (Fig. 3b) caused low-level wind speeds to increase again during the afternoon and evening of 25 August, coinciding with the initiation of spread event #2. By the end of August, temperatures warmed and RH values reached another relative minimum. However, surface wind conditions were not as favorable as during the major spread events. Portions of the fire were also becoming increasingly contained, either by fire suppression teams or natural barriers. As a result, extreme fire spread did not occur. Burning continued through 10 September at a slower rate of spread than the primary burning period (Figs. 1, 2). During 11-21 September, FRP dropped significantly and very slow growth was observed. The first substantial (> 12 mm) synoptic rainfall occurred on 21-22 September, effectively ending the satellite fire detection record for the Rim Fire (Fig. 2). However, smoldering and occasional weak flare-ups continued into early October. A variety of fire weather indices are currently available to forecast the potential for “extreme fire danger” across North America. In the Continental United States ...
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... fire weather forecasts commonly employ the Haines Index: an integer scale (1-6) based on two equally weighted ingredients for moisture and stability, respectively derived from a lower-level (850 or 700 hPa) dew point depression and lower atmospheric lapse rate (Haines 1988; Potter et al. 2008). The specific pressure levels used for the Haines Index calculations vary, depending on local topography. The majority of the Rim Fire’s primary burning period, including spread event s #1 and #2, was marked by a dry lower troposphere, with a low-level thermal lapse rate near dry- adiabatic. As a result, all fire weather indices, including the Haines Index, indicated maximum fire danger (value of 6) nearly every afternoon. Figure 5 highlights the high Haines Index environment on the first afternoon of spread event #1 (22 August), using the NARR-derived sounding for the Rim Fire coincident with the Aqua MODIS overpass at 2130 UTC. The upper limit of the Haines Index can be extended for increased sensitivity to the most extreme fire danger (Mills and McCaw 2010). However, this “Continuous Haines Index” also produced values near the 95 percentile of fire danger (value of ~8-10). Therefore, lower-atmospheric fire weather indices, such as the Haines Index, lack the fidelity for distinguishing days with extreme fire spread from those with more gradual spread. During the Rim Fire, the largest spread and FRP was generally initiated as an upper-level disturbance passed over (or near) the fire (Fig. 3). A similar link has been highlighted by previous studies (e.g., Brotak and Reifsnyder 1977; Westphal and Toon 1991; Werth and Ochoa 1993). The impact on surface wind speed and RH is inferred from Fig. 6, using hourly observations from the Remote Automatic Weather Station (RAWS, at Crane Flat Lookout (37.76 N, 119.82 W, elevation of 2025.1 m; Fig. 1). These data confirm that spread event #1 coincided with some of ...
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... 6. Primary burning period surface observations (black curve) of hourly mean wind speed (top) and relative humidity (bottom) from the RAWS station at Crane Flat Lookout ( located within Yosemite National Park at 37.76°N, 119.82°W (Fig. 1), with an elevation of 2025.1 m (6644 ft). Daytime (green triangles) and nighttime means (blue circles) were calculated using the hours of 16-03 UTC (9 AM - 8 PM) and 04-15 UTC (9 PM - 8 AM), respectively. The time series of cumulative fire area based on nighttime NIROPS observations is displayed in red. Spread events #1 and #2 are highlighted with yellow shading, and the approximate time of the shortwave passage (8/25, evening) is denoted by the dashed brown vertical line.
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... and relative humidity (bottom) from the RAWS station at Crane Flat Lookout ( located within Yosemite National Park at 37.76 N, 119.82 W (Fig. 1), with an elevation of 2025.1 m (6644 ft). Daytime (green triangles) and nighttime means (blue circles) were calculated using the hours of 16-03 UTC (9 AM - 8 PM) and 04-15 UTC (9 PM - 8 AM), respectively. The time series of cumulative fire area based on nighttime NIROPS observations is displayed in red. Spread events #1 and #2 are highlighted with yellow shading, and the approximate time of the shortwave passage (8/25, evening) is denoted by the dashed brown vertical ...
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... Using these resources, the limitations of traditional fire weather indices and conflicting hypotheses surrounding pyroCb development are examined. Variations in smoke plume altitude and transport are also explored. Therefore, the analysis of the Rim Fire is an important step toward improving methodologies currently used for regional fire weather, air quality, and visibility forecasts. Using nightly airborne-based observations, the United States Forest Service (USFS) National InfraRed OPerationS (NIROPS) provides fire perimeter maps and burned area estimates for many fire events, especially when there is an immediate risk to life and property ( NIROPS analyses were posted at an irregular schedule during the Rim Fire, generally between 03 and 09 UTC (9 PM - 3 AM local time). Figure 1 displays the estimated daily fire progression based on the NIROPS observation closest to local midnight each day. Steady growth was observed for the first two days (17-18 August), with the fire front generally spreading in all directions. On 19 August, the front was displaced noticeably to the south. By 20 August, the direction of spread shifted to the east-northeast and the rate of spread increased further, exploding in relative size during the evening of 21 August. As shown in Fig. 2 (red curve), this period of extreme fire spread (spread event #1) persisted through 23 August, burning 36206 ha (~35% of the total burned area). A second significant spread event (#2) began during the evening of 25 August, and burned 12067 ha (~12% of the total) by the evening of 26 August. Several space-borne sensors have fire detection capabilities, and are typically used in combination with (or in place of) NIROPS burned area estimates. The ...
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Wildland fires are responsible for large socio-economic impacts. Fires affect the environment, damage structures, threaten lives, cause health issues, and involve large suppression costs. These impacts can be mitigated via accurate fire spread forecast to inform the incident management team. We show that a fire forecast system based on a numerical...
Citations
... During June-August 2013, 88 enormous wildfires were observed in Western North America, producing 26 intense pyroCb storms [24]. One of the biggest wildfires in the history of California was reported to burn around 104,000 ha of land and created two intense pyroCb events [25]. ...
... Still, no literature work has been reported yet on the charge structure of pyroCb thunderclouds or analysis of the electrical conditions that favour pyroCb lightning discharge. But the scenario in pyroCb storms is generally facilitated by strong wind-shear and undiluted updraft, which raise the possibility of pyroCb thunderclouds forming the charge configurations mentioned above [20], [25], [34], [35]. ...
This paper demonstrates a 2-D numerical model to represent two conceptual pyrocumulonimbus (pyroCb) thundercloud structures: i) tilted dipole and ii) tripole structure with enhanced lower positive charge layer, which are hypothesized to explain the occurrence of lightning flashes in pyroCb storms created from severe wildfire events. The presented model considers more realistic thundercloud charge structures to investigate the electrical states and determine surface charge density for identifying potential lightning strike areas on Earth. Simulation results on dipole structure-based pyroCb thunderclouds confirm that the wind-shear extension of its upper positive (UP) charge layer by 2–8 km reduces the electric field and indicates the initiation of negative surface charge density around the earth periphery underneath the anvil cloud. These corresponding lateral extensions have confined the probable striking zone of –CG and +CG lightning within 0–23.5 km and 23.5–30 km in the simulation domain. In contrast, pyroCb thundercloud possessing the tripole structure with enhanced lower positive charge develops a negative electric field at the cloud's bottom part to block the progression of downward negative leader and cause the surface charge density beneath the thundercloud to become negative, which would lead to the formation of +CG flashes. Later, a parametric study is conducted assuming a positive linear correlation between the charge density and aerosol concentration to examine the effect of high aerosol concentration on surface charge density in both pyroCb thunderclouds. The proposed model can be expanded into 3-D to simulate lightning leader movement, aiding wildfire risk management.
... PyroCb development is a dynamic process of fire-atmospheric coupling that is driven by the interaction of large and vigorous wildfires and favorable meteorological conditions. Most pyroCb events begin with an extreme fire capable of developing a deep convective plume, while requiring instability and moisture aloft to facilitate condensation, latent heat release, and subsequent enhancement of the buoyancy of growing convective cells [9,[17][18][19]. Therefore, analysis and prediction of pyroCb development is often based on atmospheric indices, which measure atmospheric instability, and surface-based fire risk indices, which measure the potential for fire development. ...
... This is especially true in Victoria, where CA is the only variable that is significant in the univariate models for almost all subsets. This may be because CA, the temperature lapse component, has the potential to identify plumedominated fire behavior, which is necessary for most pyroCb development [9,17]. But not all plume-dominated fires have sufficient potential to cause a pyroCb, and this process is also influenced by fire intensity, fire geometry, upper wind speed and other meteorological and geographical conditions [28,29,47]. ...
The incidence of pyro-cumulonimbus (pyroCb) caused by extreme wildfires has increased markedly in Australia over the last several decades. This increase can be associated with a dangerous escalation of wildfire risk and severe stratospheric pollution events. Atmospheric and fuel conditions are important influences on pyroCb occurrence, but the exact causal relationships are still not well understood. We used the Continuous Haines Index (C-Haines) to represent atmospheric instability and the Fuel Moisture Index (FMI) to represent fuel moisture to provide better insight into the effects of atmospheric and fuel conditions on pyroCb occurrence over southeast Australia. C-Haines and FMI were related to the probability of pyroCb occurrence by employing a logistic regression on data gathered between 1980 and 2020. Emphasis is placed on investigating the independent effects and combined effects of FMI and C-Haines, as well as assessing their potential to predict whether a pyroCb develops over a fire. The main findings of this study are: (1) high C-Haines and low FMI values are representative of favorable conditions for pyroCb occurrence, but C-Haines can offset the effect of FMI—the addition of C-Haines to the logistic model muted the significance of FMI; (2) among the components of C-Haines, air temperature lapse rate (CA) is a better predictor of pyroCb occurrence than the dryness component (CB); (3) there are important regional differences in the effect of C-Haines and FMI on pyroCb occurrence, as they have better predictive potential in New South Wales than in Victoria.
... Research on wildfires in the western United States focused on the relationship between climate and wildfires [19][20][21][22][23]. For example, Sierra Nevada in California experienced several catastrophic wildfires owing to the early warming in spring and summer in recent years [24][25][26][27]. Although climate is the dominant factor in the occurrence of large wildfires, other factors such as land cover and topographic features also play an important role [28][29][30][31][32]. Land use types influence forest wildfire regimes (particularly fire size, interval, and intensity) through differences in fuel accumulation and vegetation structure [33][34][35][36]. ...
... In addition, there is less vegetation and accumulated fuel on steeper slopes, so the vegetation structure is less flammable [64,65]. However, Mermoz et al. (2005) [64] and Carmo et al. (2011) [33] found that wildfires are more likely to occur on steep slopes, and explained that land cover types on steep slopes were most likely to burn [24,66]. In this study, the western United States is less populated, and steep slopes are less covered by vegetation and less accessible to human beings. ...
... In contrast, slopes of 5%-25% are found to have higher fire proneness. It could be explained that wildfires spread more rapidly on less steep but vegetation-abundant slopes [24,65]. ...
Understanding the role of land use type and topographic features in shaping wildfire regimes received much attention because of the intensification of wildfire activities. The intensifying wildfires in the western United States are a great concern both for the environment and society. We investigate the patterns of wildfire occurrence in the western United States at the landscape level by using 118 wildfires with areas greater than 405 ha in the study year of 2018. The selection ratios were calculated to measure fire preference with regard to land cover type, slope, and aspect. The results suggest that grasslands, steeper slopes, and south-facing aspects were more susceptible to wildfires in the western United States. Additionally, there were regional variations in wildfire susceptibility in Washington, Oregon, and California. The most wildfire-prone land cover type in Washington was mixed forests, whereas that in Oregon and California was grassland. The findings of this study improve the understanding of the role of land use changes and topographic features in shaping wildfire patterns in the western United States, providing insights for managing wildfire risks for forest management strategies at the landscape level.
... D. Fromm et al., 2008a;M. D. Fromm et al., 2008b), Yosemite National Park, California in 2013 (Peterson et al., 2015), the Great Slave Lake, Northwest Territories in 2014 , and central British Columbia in 2017 (Ansmann et al., 2018;Baars et al., 2019;Peterson et al., 2018; among others. In addition, a large number of PyroCb events have been occurring in recent years around the annual bushfires of southeastern Australia and have garnered significant amounts of interest and study (Cruz et al., 2012;Dowdy et al., 2017;M. ...
Pyrocumulonimbus (PyroCb) clouds have a complex origin dependent on fire dynamics and meteorological conditions. When a pyrocumulonimbus cloud develops and is maintained over a period of time, it can inject significant aerosol into the troposphere and lower stratosphere, resulting in a longer‐term (months to years) occurrence of aerosol in the stratosphere. In this work, we investigate the British Columbia wildfires on 12–13 August 2017 using a multi‐scale simulation framework. We use the output of a physics‐based wildfire model (FIRETEC) with parameterized energy, particle, and gas emissions to drive the upper atmospheric aerosol mass injection within a regional cloud resolving model (HIGRAD). We demonstrate that vertical motions produced by latent heat release of the condensation of ice and cloud particles within the PyroCbs induce another 5 km of lifting of the simulated aerosol plume. Primary black carbon and organic aerosols (OAs) alone may not be enough to explain the observed aerosol burden, thus we show that secondary OA produced via condensation of gases by the fires, ash, and possibly dust can enhance lofted aerosol mass. A simulation with all emission mechanisms active, driven by the observed fuel load and environmental conditions, reasonably reproduces an aerosol profile inferred from observational data.
... Large scale atmospheric campaigns in temperate regions began specifying wildfires as targets during NASA's ARCTAS 2008 and SEAC 4 RS 2013 (Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys) . The latter included detailed evaluation of the plume from the Rim Fire, which was one of the largest known wildfires in California at the time (Forrister et al., 2015;Peterson et al., 2015;Saide et al., 2015;Yates et al., 2016;Yu et al., 2016). SEAC 4 RS also measured emissions and smoke evolution from 15 small agricultural fires in the Mississippi River Valley (MRV) (Liu et al., 2016). ...
The NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) experiment was a multi‐agency, inter‐disciplinary research effort to: (a) obtain detailed measurements of trace gas and aerosol emissions from wildfires and prescribed fires using aircraft, satellites and ground‐based instruments, (b) make extensive suborbital remote sensing measurements of fire dynamics, (c) assess local, regional, and global modeling of fires, and (d) strengthen connections to observables on the ground such as fuels and fuel consumption and satellite products such as burned area and fire radiative power. From Boise, ID western wildfires were studied with the NASA DC‐8 and two NOAA Twin Otter aircraft. The high‐altitude NASA ER‐2 was deployed from Palmdale, CA to observe some of these fires in conjunction with satellite overpasses and the other aircraft. Further research was conducted on three mobile laboratories and ground sites, and 17 different modeling forecast and analyses products for fire, fuels and air quality and climate implications. From Salina, KS the DC‐8 investigated 87 smaller fires in the Southeast with remote and in‐situ data collection. Sampling by all platforms was designed to measure emissions of trace gases and aerosols with multiple transects to capture the chemical transformation of these emissions and perform remote sensing observations of fire and smoke plumes under day and night conditions. The emissions were linked to fuels consumed and fire radiative power using orbital and suborbital remote sensing observations collected during overflights of the fires and smoke plumes and ground sampling of fuels.
... The process is broadly used to assess the chances for the plume to reach lifting condensation level (LCL) or convective condensation level (CCL) and the likelihood of pyroconvection phenomena (Charney & Potter, 2017;Tory et al., 2018). The most common vertical profile producing pyroCu/Cb formation (Goens & Andrews, 1998;Johnson et al., 2014;Lareau & Clements, 2016;Peterson et al., 2015Peterson et al., , 2017 is identified as a well-mixed dry ABL with a moist layer on top. In a SkewT diagram, a classic inverted-V shape can identify these conditions (Beebe, 1955;Wakimoto, 1985). ...
Pyrocumulus (pyroCu) formation during convective fire‐atmosphere interaction is a driving factor causing extreme and unpredictable wildfires. Here, by investigating several cases of pyroCu occurrence, we have monitored fire‐induced changes in atmospheric boundary layer (ABL) vertical profiles of state variables (temperature, humidity, and wind). Particular emphasis is placed in relating them to observed versus modeled fire spread biases. To this end, during the 2021 fire season in the Iberian Peninsula, we conducted a pyroconvection monitoring campaign. We gathered data on hourly fire spread, plume surface, deepening and penetration stages, and in‐situ radiosoundings within wildfire plumes. European Centre for Medium‐Range Weather Forecasts ERA5 weather data completed the analysis as reference modeling information to characterize the meso and synoptic scales on the thermodynamic profiles. We propose a novel classification of pyroconvection‐type events based on (a) differences in ABL thermodynamic stability, (b) regions characterized by high turbulence in the sub or pyroCu‐layers, and (c) the reinforced entrainment of free‐tropospheric air on top of every convective plume. This classification defines four types: (a) convective plumes, (b) overshooting pyroCu, (c) resilient pyroCu, and (d) deep pyroCu/pyroCb. Those prototypes change ABL conditions (temperature, humidity, height) differently depending on the dry or moist convection enhancement that drives them. Using this distinct behavior, we find correlations between observed ABL thermodynamic changes after fire‐atmosphere interaction and fire spread biases. Our findings pave the way to quantify the pyroconvection effect on fire spread and facilitate safer and more physically sound decisions when analyzing extreme fires.
... A key feature to note is the increased transport of Saharan dust into the Caribbean during JJA [46][47][48], observed by CATS. Additionally, we find the increased detection and transport of smoke associated with seasonal biomass burning over northwestern North America [49,50], the Amazon [51,52], and over central and southern Africa [53,54] in JJA and SON. ...
... This difference can be attributed to differences in the thresholds and wavelengths used in each algorithm to discriminate dust from dust mixed with other aerosol types. Additionally, owing to the incorporation of the MERRA-2 aerosol information content, the V3-00 CATS algorithm depicts the downwind transport of pollution originating from Asia over the north Pacific Ocean [55,56] and smoke associated with biomass burning in the US Pacific Northwest between the surface and 4 km [49,50]. ...
Concentrations of particulate aerosols and their vertical placement in the atmosphere determine their interaction with the Earth system and their impact on air quality. Space-based lidar, such as the Cloud–Aerosol Transport System (CATS) technology demonstration instrument, is well-suited for determining the vertical structure of these aerosols and their diurnal cycle. Through the implementation of aerosol-typing algorithms, vertical layers of aerosols are assigned a type, such as marine, dust, and smoke, and a corresponding extinction-to-backscatter (lidar) ratio. With updates to the previous aerosol-typing algorithms, we find that CATS, even as a technology demonstration, observed the documented seasonal cycle of aerosols, comparing favorably with the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) space-based lidar and the NASA Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) model reanalysis. By leveraging the unique orbit of the International Space Station, we find that CATS can additionally resolve the diurnal cycle of aerosol altitude as observed by ground-based instruments over the Maritime Continent of Southeast Asia.
... The Rim fire started on August 17, 2013, in a remote area of the Stanislaus National Forest near the confluence of the Clavey and Tuolumne Rivers, about 29 km east of Sonora, California (Tuolumne County) (Van Gerrevink and Veraverbeke 2021) and spread rapidly to August 31, 2013, due to rising temperature, high near-surface wind speed, and low relative humidity (Peterson et al. 2015). Within a few weeks, it expanded further north and east, burning 257,314 acres (104,131 hectares or 402 square miles) of the Stanislaus National Forest (NF), Nos Yosemite National Park (CALFIRE 2013;USDA 2014;Stavros et al. 2016), making it the largest recorded fire in the Sierra Nevada Mountains ( Fig. 1). ...
One of the crucial components in improving the quality of forests is post-fire vegetation regrowth monitoring. This is done by analyzing the time series of satellite data and studying the severity of forest fires to improve the ability to monitor the dynamic changes of the forest. This study investigates the regeneration process of existing vegetation types in different severities of The Rim fire in Sierra Nevada, California, using the time series of vegetation indices obtained from the MODIS sensor. The Vegetation Return Period (VRP) and the Recovery Rate (RR) after the fire were evaluated to monitor the regrowth of vegetation types. According to the results, the VRP values of the species for low, moderate, and high severity were estimated to be between 22 to 33 months, 33 to 47 months, and about 5 years, in this area. The 8-year changes in the time series of vegetation indices confirm that some vegetation types in this region have not fully recovered. In addition, spatio-temporal variations of the burned regions were examined with Landsat images at 2-year post-fire intervals until 2021. The results showed that in three 2-year periods after the fire, 16,074 hectares, 48,722 hectares, and 27,391 hectares of land were, respectively, converted into unburned areas, and until 2019, about 60% of the burned areas were recovered. Researchers and land managers can use the results of such studies to identify areas that need more attention after a fire.
... As the air ascends, moisture can condense releasing latent heat, which enhances convection and results in the formation of pyrocumulus (pyroCu) or pyrocumulonimbus (pyroCb) clouds [4]. In cases of deeper convection, the fire may form a firestorm, leading to (a) intense updrafts and downdrafts that can modify surface winds and affect fire spread [5][6][7], (b) lightning activity that can spark new ignitions [8], (c) the formation of tornados [9,10] and (d) stratospheric smoke injections [9,11,12] that may even alter the atmospheric chemistry [13] and have synoptic weather impacts [14,15]. The feedbacks between firestorm and surface atmospheric conditions may lead to an unpredictable and hazardous fire behaviour. ...
... Several authors have related the presence of pyroconvective events to an inverted-V atmospheric profile [5,20,21], consisting of a dry and unstable lower layer overlaid by a relatively moist middle troposphere. However, upper-and mid-tropospheric conditions also seem to play an important role in the development of deep pyroconvection [12,17]. ...
... Some authors claim that the fire-released moisture can constitute a large part of the water content in the fire plume [22], having a significant impact on the development of pyroconvection [10]. However, other studies point to fire-released sensible heat and midlevel moisture entrainment as much more relevant contributors [12,21,23,24]. Lareau and Clements [25] measured the relative importance of these factors by comparing the ambient lifted condensation level with the height of the base of pyroCu clouds, finding that the moisture release during combustion is of secondary importance in the convective process. ...
Deep pyroconvection associated with the development of firestorms, can significantly alter wildfire spread, causing severe socioeconomic and environmental impacts, and even posing a threat to human's lives. However, the limited number of observations hinders our understanding of this type of events. Here, we identify the environmental conditions that favour firestorm development using a coupled fire-atmosphere numerical model. From climate model projections for the 21st century, we show that the number of days with deep pyroconvection risk will increase significantly in southern Europe, especially in the western Mediterranean region, where it will go from between 10 and 20 days per year at present to between 30 and 50 days per year by the end of the century. Our results also suggest fuel reduction as an effective landscape management strategy to mitigate firestorm risks in the future.
... In an examination of the 2013 Rim Fire (California), Peterson et al. (2015) employed FRP estimates from the GOES-14 satellite to study extreme fire spread and pyroconvection. Peaks in FRP during the Rim Fire likely coincided with the most intense burning (Fig. 3.7). ...
... Peaks in FRP during the Rim Fire likely coincided with the most intense burning (Fig. 3.7). Although diurnal variability in FRP is evident, it is equally evident that variation in FRP does not follow a simple diurnal distribution as Peterson et al. (2015) described for the Western Regional Air Partnership and Western Governors Association (Air Resources Inc. 2005). The co-occurrence of high FRP on days with weaker atmospheric stability is likely tied to a greater vertical extent of the smoke plumes and an enhanced probability of smoke injection into the free troposphere (Val Martin et al. 2010;Peterson et al. 2014). ...
... Finer-scale models such as CAWFE may improve the resolution of fire-induced flows but lack the ability to do so operationally until faster computers or more computationally efficient approaches are available. However, these retrospective approaches have the potential to help in planning and prioritizing areas of the landscape where fuels, weather, and topography might create fire-atmosphere coupling characteristic of some large wildfires [e.g., the previously mentioned Rim fire (Peterson et al. 2015) and King fire (Coen et al. 2018)]. ...
Recent large wildfires in the USA have exposed millions of people to smoke, with major implications for health and other social and economic values. Prescribed burning for ecosystem health purposes and hazardous fuel reduction also adds smoke to the atmosphere, in some cases affecting adjacent communities. However, we currently lack an appropriate assessment framework that looks past the planned versus unplanned nature of a fire and assesses the environmental conditions under which particular fires burn, their socio-ecological settings, and implications for smoke production and management. A strong scientific foundation is needed to address wildland fire smoke challenges, especially given that degraded air quality and smoke exposure will likely increase in extent and severity as the climate gets warmer. It will be especially important to provide timely and accurate smoke information to help communities mitigate potential smoke impacts from ongoing wildfires, as well as from planned prescribed fires. This assessment focuses on primary physical, chemical, biological, and social considerations by documenting our current understanding of smoke science and how the research community can collaborate with resource managers and regulators to advance smoke science over the next decade.
