Lightning-caused Wildfires Research Articles

Human-related ignitions concurrent with high winds promote large wildfires across the USA

Large wildfires (>40 ha) account for the majority of burned area across the contiguous United States (US) and appropriate substantial suppression resources. A variety of environmental and social factors influence wildfire growth and whether a fire overcomes initial attack efforts and becomes a large wildfire. However, little is known about how these factors differ between lightning-caused and human-caused wildfires. This study examines differences in temperature, vapour pressure deficit, fuel moisture and wind speed for large and small lightning- and human-caused wildfires during the initial days of fire activity at ecoregion scales across the US. Large fires of both human and lightning origin occurred coincident with above-normal temperature and vapour pressure deficit and below-normal 100-hour dead fuel moisture compared with small fires. Large human-caused wildfires occurred, on average, coincident with higher wind speeds than small human-caused wildfires and large lightning-caused wildfires. These results suggest the importance of winds in driving rapid fire growth that can allow fires to overcome many of the factors that typically inhibit large human-caused fires. Additionally, such findings highlight the interplay between human activity and meteorological conditions and the importance of incorporating winds in modelling large-fire risk in human-dominated landscapes.

The rainfall factor in lightning-ignited wildfires in Catalonia

Wildland fires originated by lightning in Catalonia (NE Spain) are systematically examined through the use of lightning and precipitation data. The region of study, with a Mediterranean climate, is prone to summer wildfires. Despite being mainly anthropogenic, lightning-ignited fires (10%) are relevant as they can trigger large fires. Given that the lightning efficiency in Catalonia is of 1/1400 fires per lightning, the ability to identify potential ignition candidates among the whole lightning population would be of great value to forest protection agencies. Literature reveals that lightning characteristics such as polarity or multiplicity has proven to be of limited value as predictors. Therefore, another approach is necessary to set a probability of wildfire ignition to each lightning. In this regard, the aim of this study was to explore the relationship between lightning-ignited wildfires and precipitation, as lightning-ignited wildfires in the region are often attributed to ‘dry’ lightning (lightning accompanied with little or no precipitation). Results revealed that 25% of the lightning strokes related to wildfire ignitions had no associated precipitation at all, 40% had less than 2mm of precipitation and 90% had less than 10mm. Results also revealed that holdover fires (ignitions with delayed arrivals) are rare in the region. Finally, results suggest that there is no apparent link between the amount of precipitation and the holdover duration, indicating that the survival phase of lightning-ignitions is mainly driven by the daily cycle of solar heating. All in all, adding information on the precipitation associated to each lightning may help focusing attention on a reduced sample of strokes and provide fire managers with valuable information about potential lightning-caused wildfires.

Some Wildfire Ignition Causes Pose More Risk of Destroying Houses than Others.

Many houses are at risk of being destroyed by wildfires. While previous studies have improved our understanding of how, when and why houses are destroyed by wildfires, little attention has been given to how these fires started. We compiled a dataset of wildfires that destroyed houses in New South Wales and Victoria and, by comparing against wildfires where no houses were destroyed, investigated the relationship between the distribution of ignition causes for wildfires that did and did not destroy houses. Powerlines, lightning and deliberate ignitions are the main causes of wildfires that destroyed houses. Powerlines were 6 times more common in the wildfires that destroyed houses data than in the wildfires where no houses were destroyed data and lightning was 2 times more common. For deliberate- and powerline-caused wildfires, temperature, wind speed, and forest fire danger index were all significantly higher and relative humidity significantly lower (P < 0.05) on the day of ignition for wildfires that destroyed houses compared with wildfires where no houses were destroyed. For all powerline-caused wildfires the first house destroyed always occurred on the day of ignition. In contrast, the first house destroyed was after the day of ignition for 78% of lightning-caused wildfires. Lightning-caused wildfires that destroyed houses were significantly larger (P < 0.001) in area than human-caused wildfires that destroyed houses. Our results suggest that targeting fire prevention strategies around ignition causes, such as improving powerline safety and targeted arson reduction programmes, and reducing fire spread may decrease the number of wildfires that destroy houses.

Controls on interannual variability in lightning-caused fire activity in the western US

Lightning-caused wildfires account for a majority of burned area across the western United States (US), yet lightning remains among the more unpredictable spatiotemporal aspects of the fire environment and a challenge for both modeling and managing fire activity. A data synthesis of cloud-to-ground lightning strikes, climate and fire data across the western US from 1992 to 2013 was conducted to better understand geographic variability in lightning-caused wildfire and the factors that influence interannual variability in lightning-caused wildfire at regional scales. Distinct geographic variability occurred in the proportion of fires and area burned attributed to lightning, with a majority of fires in the interior western US attributed to lightning. Lightning ignition efficiency was highest across the western portion of the region due to the concomitance of peak lightning frequency and annual nadir in fuel moisture in mid-to-late summer. For most regions the number of total and dry lightning strikes exhibited strong interannual correlation with the number of lightning-caused fires, yet were a poor predictor of area burned at regional scales. Commonality in climate–fire relationships for regional annual area burned by lightning- versus human-ignited fires suggests climate conditions, rather than lightning activity, are the predominant control of interannual variability in area burned by lightning-caused fire across much of the western US.

Assessing possible shifts in wildfire regimes under a changing climate in mountainous landscapes

Climate change may affect the probability of extreme events such as wildfires. Although wildfires are some of the most important ecological processes in forest ecosystems, large-scale wildfires are often perceived as an environmental disaster. Since failure to include the dynamic nature of ecosystems in planning will inevitably lead to unexpected outcomes, we need to enhance our ability to cope with future extreme events coupled with climate change. This study presents several future scenarios in three different time periods for Canada’s Columbia Montane Cordillera Ecoprovince, which is prone to wildfires. These scenarios predict the probability of occurrence of widespread wildfires based on the hierarchical Bayesian model. The model was based on the relationships between wildfires and the Monthly Drought Code (MDC). The MDC is a generalized monthly version of the Daily Drought Code widely used across Canada by forest fire management agencies for monitoring of wildfire risk. To calculate future MDC values, we relied on different possible future conditions of climate, given by the Global Circulation Models. We found a regime shift in drought intensity with abrupt decreases in lightning-caused wildfire activity around 1940, suggesting that future wildfire risks can be inferred primarily from the summer drought code. For future periods, we found increasing trends in the probabilities of large-scale fires with time in most areas. It should be notable that, by the 2080s, there is a probability of some areas having more than 50% of large-scale wildfires under the “average” climatic conditions in the future, indicating that, even without “extreme” weather conditions, some ecosystems will have a fundamental probability of experiencing catastrophic fires under the condition of average summer. However, the rate of progression toward a fire-prone condition is quite different among the three climate change scenarios and among the region analyzed. Given such scenario-sensitive, spatially-heterogeneous patterns of wildfire probability in response to climate variability, management strategy should be flexible and more localized. By drawing on this knowledge, it may be possible to mitigate climate change impacts both before they arise and once they have occurred. These considerations are critical for maintaining the integrity of systems shaped by large-scale natural disturbances to increase their resilience to the changing climate while protecting human society and infrastructures. Working with alternative scenarios will facilitate our adaptation to climate change in managing fire-prone forest ecosystems.

Influences of forest roads on the spatial patterns of human- and lightning-caused wildfire ignitions

Understanding the spatial patterns of fire ignitions and fire sizes is essential for understanding fire regimes. Although previous studies have documented associations of human-caused fire ignitions with road corridors, less consideration has been given to understanding the multiple influences of roads on the fire regime at a broader landscape-scale. Therefore, we examined the difference between lightning- and human-caused fire ignitions in relation to forest road corridors and other anthropogenic and biophysical factors in the eastern Cascade Mountains of Washington State. We used geographical information systems and case-control logistic regression models to assess the relative importance of these explanatory variables that influence the locations of lightning versus human-caused ignitions. We found that human-caused ignitions were concentrated close to roads, in high road density areas, and near the wildland–urban interface (WUI). In contrast, lightning-caused ignitions were concentrated in low road density areas, away from WUI, and in low population density areas. Lightning-caused ignitions were also associated with fuels and climatic and topographic factors. A weak but significant relationship between lightning-caused fire and proximity to gravel roads may be related to fuels near roads or to bias in detection and reporting of lightning-caused fires near roads. Although most small fires occurred in roaded areas, they accounted for only a small proportion of the total burned area. In contrast, the large fires in roadless and wilderness areas accounted for most of the burned area. Thus, from the standpoint of the total area burned, the effect of forest roads on restricting fire size is likely greater than the impact of roads on increasing fire ignitions. The results of our study suggest that roads and their edge effect area should be more widely acknowledged as a unique type of landscape effect in fire research and management.

Short-Term Effects of a Summer Wildfire on a Desert Grassland Arthropod Community in New Mexico

Surface-active arthropods were sampled after a lightning-caused wildfire in desert grassland habitat on the Sevilleta National Wildlife Refuge, Socorro County, NM. Pitfall traps (n = 32 per treatment) were used to evaluate species-specific "activity-density" indices after the June wildfire in both burned and unburned areas. In total, 5,302 individuals were collected from 69 taxa. Herbivore activity-densities generally decreased, whereas predators often increased in the burned area; pitfall trap bias likely contributed to this latter observation. Fire caused the virtual extirpation of scaly crickets (Mogoplistidae), field crickets (Gryllidae), and camel crickets (Raphidophoridae), but recolonization began during the first postfire growing season. Several grasshoppers (Acrididae) also exhibited significant postfire declines [Ageneotettix deorum (Scudder), Eritettix simplex (Scudder), Melanoplus bowditchi Scudder, and Amphitornus coloradus (Thomas)]. Some beetles showed lower activity-density, including Pasimachus obsoletus LeConte (Carabidae) and Eleodes extricatus (Say) (Tenebrionidae). Taxa exhibiting significant postfire increases in activity-density included acridid grasshoppers (Aulocara femoratum (Scudder), Hesperotettix viridis (Thomas), Trimerotropis pallidipennis (Burmeis.), and Xanthippus corallipes Haldeman); carabid beetles (Amblycheila picolominii Reiche, Cicindela punctulata Olivier), tenebrionid beetles (Eleodes longicollis LeConte, Edrotes rotundus (Say), Glyptasida sordida (LeConte), Stenomorpha consors (Casey); the centipedes Taiyubius harrietae Chamberlin (Lithobiidae) and Scolopendra polymorpha Wood (Scolopendridae); scorpions (Vaejovis spp.; Vaejovidae); and sun spiders (Eremobates spp.; Eremobatidae). Native sand roaches (Arenivaga erratica Rehn, Eremoblata subdiaphana (Scudder); Polyphagidae) displayed no significant fire response. Overall, arthropod responses to fire in this desert grassland (with comparatively low and patchy fuel loads) were comparable to those in mesic grasslands with much higher and more continuous fuel loads.

A parametric model of the fire-size distribution

This paper developes statistical models of the size distribution of lightning-caused wildfires in the boreal mixedwood forests of Alberta, Canada, for the intervals 1980––1998 and 1961––1998. Above any minimum threshold size [Formula: see text]3 ha, the logarithm of fire size is approximately exponentially distributed. However, computer simulations using the best-fit distribution would over predict the frequency of large fires, and thus the mean rate of disturbance. A truncated exponential distribution, which places an upper bound on fire size, is more suitable and, according to probability plots, provides an excellent fit to the data. I estimate the maximum fire size in the study area to be [Formula: see text] 650 000 ha. This estimate is insensitive to the choice of lower bound for fire sizes (between 3 and 1000 ha) and to the choice of sampling interval. Parametric modelling of fire sizes using covariates derived from forest inventory data shows that the expected size of a fire is positively related to the abundance of pine forest in the vicinity of the point of detection and negatively related to the abundance of recently logged or burnt areas. This implies that variation in forest structure and disturbance history impose marked spatial variability on the fire size distribution. Other covariates, such as periodic indices of fire weather, could readily be evaluated in this framework.

The Impact of a 2 × CO2Climate on Lightning-Caused Fires

Future climate change could have significant repercussions for lightning-caused wildfires. Two empirical fire models are presented relating the frequency of lightning fires and the area burned by these fires to the effective precipitation and the frequency of thunderstorm activity. One model deals with the seasonal variations in lightning fires, while the second model deals with the interannual variations of lightning fires. These fire models are then used with the Goddard Institute for Space Studies General Circulation Model to investigate possible changes in fire frequency and area burned in a 2 X CO2 climate. In the United States, the annual mean number of lightning fires increases by 44%, while the area burned increases by 78%. On a global scale, the largest increase in lightning fires can be expected in untouched tropical ecosystems where few natural fires occur today.

Fire behaviour in spinifex fuels on the Gibson Desert Nature Reserve, Western Australia

Fire management proposed for desert conservation reserves in Western Australia will aim to recreate the fire-induced diversity that is believed to have existed for thousands of years during Aboriginal occupation. Since Aboriginal people no longer practise their traditional nomadic lifestyle, there has been a reduction in the diversity of fire regimes. There exists vast areas of long unburnt and sensescing spinifex (Triodia sp. and Plectrachne sp.) and vast areas burnt infrequently by lightning-caused wildfire. This has probably contributed to the reported decline in native fauna. In order to implement a patch burn strategy to increase habitat diversity, it is necessary to understand fuels and fire behaviour. In the Gibson Desert Nature Reserve, spinifex is the dominant fuel type and its distribution and cover were found to be closely related to landform soils. Detailed measures of fuel characteristics and the behaviour of experimental fires allowed functional models for predicting fire spread to be developed. Spinifex fires were wind-driven and spread rapidly when wind speed exceeded 12–17 kmh−1 at 2 m above ground. The patchy nature of the fuel prevented the development of a continuous fire perimeter. Crescent-shaped head fires burnt a finger-like pattern through the spinifex, unlike the typically elliptical shapes common to fires burning in continuous fuels. Direction of fire spread, hence fire scar pattern, was very responsive to shifts in wind direction.

Wildfire and the Evolution of Dorsal Melanism in Fox Squirrels, Sciurus niger

Populations of fox squirrels ( Sciurus niger ) of the southeastern United States often include melanistic individuals. The genetic determinants of melanism in fox squirrels of the lower Mississippi River drainage (Louisiana and Mississippi) appear to differ from those for melanism in fox squirrels of the rest of the southeastern U.S. coastal plain, but functional causes of the melanism could be the same in both regions. I examine the hypothesis that melanistic polymorphism may have resulted from alternating cryptic superiority of light and dark individuals as a result of intermittent blackening of substrates by wildfires. I show that frequencies of all wildfires and of lightning-caused wildfires (both normalized per unit area) over the total range of the squirrels are correlated positively with the incidence of melanistic individuals. However, when just the southeastern coastal-plain states are considered, only frequency of lightning-caused fires shows significant correlation with melanism; in the lower Mississippi River drainage region, neither measure of fire frequency shows significant positive correlations. Other climatic variables have little potential for explaining maintenance of the polymorphism. Weak sex and size correlations with melanism may be pleiotropic side-effects of genetic systems determining coloration rather than clues to the functional significance of the trait.