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Anatomy of the false link between forest fires and anthropogenic CO2
Abstract
In this critical review of the scientific literature about fire, I describe how the false notion of a link between forest fires and anthropogenic CO2 was ignited in 2006 by a fatally flawed article promoted in the science-trend-setting magazine Science, and spread like wildfire through the scientific literature and beyond, driven in part by high winds of climate modelling extravagance, while fortunately leaving large unburnt patches. There is no evidentiary basis for such a link. On the contrary, established knowledge about forest fires leads to the conclusion that dedication to teasing out such a link is preposterous: In the present circumstances starting in approximately 1900, the dominant effect is direct human impacts on land use, which causes global fire occurrences to be dramatically less than from the known long-term natural cycles (modern fire deficit). No special circumstances or regions have been correctly identified where forest fire behaviour can be attributed to CO2. Canada’s recent Fort McMurray fire is no exception. The claimed 7 g mean birth weight loss arising from mothers’ general exposure to CO2-driven southern California wildfires, like all such claims, is a product of statistical and conceptual overenthusiasm. I use concepts from the animal-behaviour scientific literature to explain how some scientists and their followers can get so carried away.
Human impact on wildfires, a major earth system component, remains
poorly understood. While local studies have found more fires close
to settlements and roads, assimilated charcoal records and analyses
of regional fire patterns from remote-sensing observations point to
a decline in fire frequency with increasing human population. Here,
we present a global analysis using three multi-year satellite-based
burned-area products combined with a parameter estimation and
uncertainty analysis with a non-linear model. We show that at the
global scale, the impact of increasing population density is mainly
to reduce fire frequency. Only for areas with up to 0.1 people
per km2, we find that fire frequency increases by 10 to
20% relative to its value at no population. The results are
robust against choice of burned-area data set, and indicate that at
only very few places on earth, fire frequency is limited by human
ignitions. Applying the results to historical population estimates
results in a moderate but accelerating decline of global burned area
by around 14% since 1800, with most of the decline since 1950.
High fire activity in western North America is associated with drought. Drought and fire prevail under negative El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) phases in the Southwest and with positive phases in the Northwest. Here, I infer climate effects on historic fire patterns in the geographically intermediate, eastern Great Basin and seek out evidence of human influence on reconstructed fire regimes. Surface fire chronologies were constructed for 10 sites using tree-ring-based fire scars. Regional (67) and local (247) fire years and no-fire (187) years were identified from 1400 to 1900 C.E. I compared fire chronologies with indices of the Palmer Drought Severity Index (PDSI), ENSO, and PDO. Regionally, fires were significantly more common during drought and were associated with negative ENSO and positive-to-negative PDO transitions while no-fire years were associated with positive ENSO and negative-to-positive PDO transitions. Conditions were significantly wetter 2 years prior to regional fire years and drier 4 years prior to no-fire years, providing evidence that fires were historically fuel limited. Local fire years occurred under a broad range of climate conditions. Most sites showed either persistent late or bimodal (early and late) fire seasonality patterns. These patterns are distinct from the mid-season peak observed for modern lightning-caused fires, suggesting a human influence on historical ignition patterns. Results demonstrate that climate was an important synchronizer of fire at the regional scale and that locally fire regimes were the product of climate-regulated fuels and some combination of human and lightning ignition patterns.
Analyses to identify and relate trends in wildfire activity to factors such as climate, population, land use or land cover and wildland fire policy are increasingly popular in the United States. There is a wealth of US wildfire activity data available for such analyses, but users must be aware of inherent reporting biases, inconsistencies and uncertainty in the data in order to maximise the integrity and utility of their work. Data for analysis are generally acquired from archival summary reports of the federal or interagency fire organisations; incident-level wildfire reporting systems of the federal, state and local fire services; and, increasingly, remote-sensing programs. This paper provides an overview of each of these sources and the major reporting biases, inconsistencies and uncertainty within them. Use of national fire reporting systems by state and local fire organisations has been rising in recent decades, providing an improved set of incident-level (documentary) data for all-lands analyses of wildfire activity. A recent effort to compile geospatial documentary fire records for the USA for 1992–2013 has been completed. The resulting dataset has been evaluated for completeness using archival summary reports and includes a linkage to a widely used, remotely sensed wildfire perimeter dataset.
Downscaled climate models provide projections of how climate change may exacerbate the local impacts of natural hazards. The extent to which people facing exacerbated hazard conditions understand or respond to climate-related changes to local hazards has been largely overlooked. In this article, we examine the relationships among climate change beliefs, environmental beliefs, and hazard mitigation actions in the context of wildfire, a natural hazard projected to be intensified by climate change. We find that survey respondents are situated across a continuum between being ‘believers’ and ‘deniers’ that is multidimensional. Placement on this believer–denier spectrum is related to general environmental attitudes. We fail, however, to find a relationship between climate change beliefs and wildfire risk-reduction actions in general. In contrast, we find a statistically significant positive relationship between level of wildfire risk mitigation and being a climate denier. Further, certain pro-environmental attitudes are found to have a statistically significant negative association with the level of wildfire risk mitigation.
Dry forests at low elevations in temperate-zone mountains are commonly hypothesized to be at risk of exceptional rates of severe fire from climatic change and land-use effects. Their setting is fire-prone, they have been altered by land-uses, and fire severity may be increasing. However, where fires were excluded, increased fire could also be hypothesized as restorative of historical fire. These competing hypotheses are not well tested, as reference data prior to widespread land-use expansion were insufficient. Moreover, fire-climate projections were lacking for these forests. Here, I used new reference data and records of high-severity fire from 1984-2012 across all dry forests (25.5 million ha) of the western USA to test these hypotheses. I also approximated projected effects of climatic change on high-severity fire in dry forests by applying existing projections. This analysis showed the rate of recent high-severity fire in dry forests is within the range of historical rates, or is too low, overall across dry forests and individually in 42 of 43 analysis regions. Significant upward trends were lacking overall from 1984-2012 for area burned and fraction burned at high severity. Upward trends in area burned at high severity were found in only 4 of 43 analysis regions. Projections for A.D. 2046-2065 showed high-severity fire would generally be still operating at, or have been restored to historical rates, although high projections suggest high-severity fire rotations that are too short could ensue in 6 of 43 regions. Programs to generally reduce fire severity in dry forests are not supported and have significant adverse ecological impacts, including reducing habitat for native species dependent on early-successional burned patches and decreasing landscape heterogeneity that confers resilience to climatic change. Some adverse ecological effects of high-severity fires are concerns. Managers and communities can improve our ability to live with high-severity fire in dry forests.
Although there is acute concern that insect-caused tree mortality increases the likelihood or severity of subsequent wildfire, previous studies have been mixed, with findings typically based on stand-scale simulations or individual events. This study investigates landscape-and regional-scale wildfire likelihood following outbreaks of the two most prevalent native insect pests in the US Pacific Northwest (PNW): mountain pine beetle (MPB; Dendroctonus ponderosae) and western spruce budworm (WSB; Choristoneura freemani). We leverage seamless census data across numerous insect and fire events to (1) summarize the interannual dynamics of insects (1970–2012) and wildfires (1984–2012) across forested ecoregions of the PNW; (2) identify potential linked disturbance interactions with an empirical wildfire likelihood index; (3) quantify this insect-fire likelihood across different insect agents, time lags, ecoregions, and fire sizes. All three disturbance agents have occurred primarily in the drier, interior conifer forests east of the Cascade Range. In general, WSB extent exceeds MPB extent, which in turn exceeds wildfire extent, and each disturbance typically affects less than 2% annually of a given ecoregion. In recent decades across the PNW, wildfire likelihood does not consistently increase or decrease following insect outbreaks. There is evidence, however, of linked interactions that vary across insect agent (MPB, WSB), space (ecoregion), and time (interval since insect onset). Specifically, in most cases following MPB activity, fire likelihood is neither higher nor lower than in non-MPB-affected forests. In contrast, fire likelihood is lower following WSB activity across multiple ecoregions and time lags. In addition, insect-fire likelihood is not consistently associated with interannual fire extent, suggesting that other factors (e.g., climate) control the disproportionately large fire years accounting for regional fire dynamics. Thus, although both bark beetles and defoliators alter fuels and associated fire potential, the windows of opportunity for increased or decreased fire likelihood are too narrow—or the phenomena themselves too rare—for a consistent signal to emerge across PNW conifer forests. These findings suggest that strategic plans should recognize (1) the relative rarity of insect-fire interactions and (2) the potential ecosystem restoration benefits of native insect outbreaks, when they do occur.
In Canadian forests, the majority of burned area occurs on a small number of days of extreme fire weather. These days lie within the tail end of the distribution of fire weather, and are often the periods when fire suppression capacity is most challenged. We examined the historic and future frequency of such extreme fire weather events across 16 fire regime zones in the forested regions of Canada from 1970 to the year 2090. Two measurements are used to measure the extreme fire weather events, the 95th percentile of Fire Weather Index (FWI 95) and the number of spread days. The annual frequency of fire spread days is modelled to increase 35–400 % by 2050 with the greatest absolute increases occurring in the Boreal Plains of Alberta and Saskatchewan. The largest proportional increase in the number of spread days is modelled to occur in coastal and temperate forests. This large increase in spread days was found despite a modest average increase in FWI 95. Our findings suggest that the impact of future climate change in Canadian forests is sufficient to increase the number of days with active fire spread. Fire management agencies in coastal and temperate regions may need to adapt their planning and capacity to deal with proportionally larger changes to their fire weather regime compared to the already high fire management capacity found in drier continental regions.
Research in the Sierra Nevada range of California, USA, has provided conflicting results about current trends of high-severity fire. Previous studies have used only a portion of available fire severity data, or considered only a portion of the Sierra Nevada. Our goal was to investigate whether a trend in fire severity is occurring in Sierra Nevada conifer forests currently, using satellite imagery. We analysed all available fire severity data, 1984–2010, over the whole ecoregion and found no trend in proportion, area or patch size of high-severity fire. The rate of high-severity fire has been lower since 1984 than the estimated historical rate. Responses of fire behaviour to climate change and fire suppression may be more complex than assumed. A better understanding of spatiotemporal patterns in fire regimes is needed to predict future fire regimes and their biological effects. Mechanisms underlying the lack of an expected climate- and time since fire-related trend in high-severity fire need to be identified to help calibrate projections of future fire. The effects of climate change on high-severity fire extent may remain small compared with fire suppression. Management could shift from a focus on reducing extent or severity of fire in wildlands to protecting human communities from fire.
A B S T R A C T Past the middle of the 20th century, forest fires started to increase markedly in the Mediterranean countries of southern Europe. Hazardous land-use and land-cover (LULC) changes are considered major drivers of increased fire-hazard and fire risk. However, the contribution of various LULC changes to increased fire-hazard, as well as the role of environmental or socioeconomic factors in driving them, including its changing role over time, are poorly known. Understanding how changes in socio-economics in interaction with other factors modify landscape fire-hazard and risk is a major priority in fire-prone areas. Here we determined changes in fire-hazard through time, focusing on the contribution of agriculture abandonment to it, and on the changing role of its driving factors, in a large (56,000 km 2) rural area in West-Central Spain. The study period covers from 1950s to 2000. LULC maps at different time steps (1950s, 1978, 1986 and 2000) were available, as well as environmental and socioeconomic information at various scales. We analyzed trends in LULC change, focusing on those altering fire-hazard, and used general linear models (GLM) with generalized linear mixed models (GLMM) to account for the effects of variables at different spatial scales in determining changes leading to shifts in fire-hazard. We found that the proportion of hazardous LULC types increased twofold (26–42%) from 1950s to 2000. Until 1986, agriculture abandonment was the dominant LULC change leading to increased fire-hazard. Post-1986, LULC changes were mainly driven by deforestation due to fires and densification caused by natural vegetation dynamics. Models showed that the first abandoned lands were driven by local environmental and socioeconomic constraints (small farms, in distant locations, in municipalities with low population), whereas later abandonments were driven by non-local ones (large farms, in more productive soils, closer to towns, populations with high unemployment, and higher employment in the services sector). Throughout the entire period, high proportion of wildland vegetation, low mechanization level, and large number of land-holders older than 55 years favored abandonment. This implies that as the population ages, larger, more accessible and productive areas are abandoned, fire-hazard will increase closer to human settlements, increasing the wild-land urban interface and fire risk. ã
Wildfires have played a determining role in distribution, composition and structure of many ecosystems worldwide and climatic changes are widely considered to be a major driver of future fire regime changes. However, forecasting future climatic change induced impacts on fire regimes will require a clearer understanding of other drivers of abrupt fire regime changes. Here, we focus on evidence from different environmental and temporal settings of fire regimes changes that are not directly attributed to climatic changes. We review key cases of these abrupt fire regime changes at different spatial and temporal scales, including those directly driven (i) by fauna, (ii) by invasive plant species, and (iii) by socio-economic and policy changes. All these drivers might generate non-linear effects of landscape changes in fuel structure; that is, they generate fuel changes that can cross thresholds of landscape continuity, and thus drastically change fire activity. Although climatic changes might contribute to some of these changes, there are also many instances that are not primarily linked to climatic shifts. Understanding the mechanism driving fire regime changes should contribute to our ability to better assess future fire regimes.
The amount, frequency, and duration of precipitation have important impact on the occurrence and severity of forest fires. To fully understand the effects of precipitation regimes on forest fires, a drought index was developed with number of consecutive dry days (daily precipitation less than 2 mm) and total precipitation, and the relationships of drought and precipitation with fire activities were investigated over two periods (i.e., 1982-1988 and 1989-2008) in five ecoregions of Yunnan Province. The results showed that precipitation regime had a significant relationship with fire activities during the two periods. However, the influence of the drought on fire activities varied by ecoregions, with more impacts in drier ecoregions IV-V and less impacts in the more humid ecoregions I-III. The drought was more closely related to fire activities than precipitation during the two study periods, especially in the drier ecoregions, indicating that the frequency and the duration of precipitation had significant influences on forest fires in the drier areas. Drought appears to offer a better explanation than total precipitation on temporal changes in fire regimes across the five ecoregions in Yunnan. Our findings have significant implications for forecasting the local fire dangers under the future climate change.
[1] The area burned by forest fires in Canada has increased over the past four decades, at the same time as summer season temperatures have warmed. Here we use output from a coupled climate model to demonstrate that human emissions of greenhouse gases and sulfate aerosol have made a detectable contribution to this warming. We further show that human-induced climate change has had a detectable influence on the area burned by forest fire in Canada over recent decades. This increase in area burned is likely to have important implications for terrestrial emissions of carbon dioxide and for forest ecosystems.
It has been suggested that on a global scale, fire activity changes along the productivity/aridity gradient following a humped relationship, i.e. the intermediate fire–productivity hypothesis. This relation should be driven by differing relative roles of the main fire drivers (weather and fuel) along the productivity gradient. However, the full intermediate fire–productivity model across all world ecosystems remains to be validated. The entire globe, excluding Antarctica. To test the intermediate fire–productivity hypothesis, we use the world ecoregions as a spatial unit and, for each ecoregion, we compiled remotely sensed fire activity, climate, biomass and productivity information. The regression coefficient between monthly MODIS fire activity and monthly maximum temperature in each ecoregion was considered an indicator of the sensitivity of fire to high temperatures in the ecoregion. We used linear and generalized additive models to test for the linear and humped relationships. Fire occurs in most ecoregions. Fire activity peaked in tropical grasslands and savannas, and significantly decreased towards the extremes of the productivity gradient. Both the sensitivity of fire to high temperatures and above-ground biomass increased monotonically with productivity. In other words, fire activity in low-productivity ecosystems is not driven by warm periods and is limited by low biomass; in contrast, in high-productivity ecosystems fire is more sensitive to high temperatures, and in these ecosystems, the available biomass for fires is high. The results support the intermediate fire–productivity model on a global scale and suggest that climatic warming may affect fire activity differently depending on the productivity of the region. Fire regimes in productive regions are vulnerable to warming (drought-driven fire regime changes), while in low-productivity regions fire activity is more vulnerable to fuel changes (fuel-driven fire regime changes).
Remote sensing can quantify past and present fire activity at spatial scales useful for a range of fire and vegetation management applications. In this study, we present a new automated approach to classifying burnt areas across the state of Queensland, Australia. The method is applied to complete time series of Landsat TM/ETM + imagery rather than single images and considers spectral (band 4, B4, and bands 4 + 5, B45), thermal, temporal and contextual information within a hierarchical framework. To maximise the available observations and the burnt area detected, we used imagery containing up to 60% cloud that was screened during pre-processing. Median filters were applied to smooth the time series and multi-date change detection used to locate negative outliers (large declines in reflectance relative to the median-smoothed time series). Watershed region growing was used to segment and map a larger spatial extent of the change while minimising commission errors. These segmented change objects were attributed as either burnt or unburnt using their thermal, reflective and contextual characteristics in a classification tree. Thermal information was found to be more important than reflective indices in the change attribution. Algorithm calibration used training data from ten Path/Rows located strategically across Queensland with four images sampled per path row (n = 40). Thresholds were optimised to maximise the burnt area detected while limiting under/over-growing of burnt area. Validation data covered a range of burnt areas from ten independent Path/Rows with ten images sampled across a range of burnt area fractions per Path/Row (n = 100). The results for burnt area mapping demonstrated an average producer's accuracy of 85% (range of 28 to 100% for individual images) and average user's accuracy of 71% (range of 4 to 99% for individual images). A morphological dilation of one pixel restricted to locations exhibiting a decline in B45 over time, increased the producer's accuracy by 4% but reduced the user's accuracy by 8%. The total accuracy for the burnt area classification was greater than 99%, however this is more a reflection of the small fraction of landscape represented by burnt area rather than the ability to detect burnt area. Areas frequently misclassified were related to areas of high spectral/land use change which included areas of cropping, frequently inundated land, and moisture/ground cover variations over dark soils. In this study, we applied a crop and water mask to minimise commission errors. Significantly, the results of this study demonstrate that an automated time series method for mapping burnt areas can be successfully applied across a diversity of land cover types. The method may be applied in similar savanna dominated environments but is likely to require modification to be applicable in other landscapes.
Understanding the fire prediction capabilities of fuel models is vital to forest fire management. Various fuel models have been developed in the Great Xing'an Mountains in Northeast China. However, the performances of these fuel models have not been tested for historical occurrences of wildfires. Consequently, the applicability of these models requires further investigation. Thus, this paper aims to develop standard fuel models. Seven vegetation types were combined into three fuel models according to potential fire behaviors which were clustered using Euclidean distance algorithms. Fuel model parameter sensitivity was analyzed by the Morris screening method. Results showed that the fuel model parameters 1-hour time-lag loading, dead heat content, live heat content, 1-hour time-lag SAV(Surface Area-to-Volume), live shrub SAV, and fuel bed depth have high sensitivity. Two main sensitive fuel parameters: 1-hour time-lag loading and fuel bed depth, were determined as adjustment parameters because of their high spatio-temporal variability. The FARSITE model was then used to test the fire prediction capabilities of the combined fuel models (uncalibrated fuel models). FARSITE was shown to yield an unrealistic prediction of the historical fire. However, the calibrated fuel models significantly improved the capabilities of the fuel models to predict the actual fire with an accuracy of 89%. Validation results also showed that the model can estimate the actual fires with an accuracy exceeding 56% by using the calibrated fuel models. Therefore, these fuel models can be efficiently used to calculate fire behaviors, which can be helpful in forest fire management.
Time-varying fire-climate relationships may represent an important component of fire-regime variability, relevant for understanding the controls of fire and projecting fire activity under global-change scenarios. We used time-varying statistical models to evaluate if and how fire-climate relationships varied from 1902-2008, in one of the most flammable forested regions of the western U.S.A. Fire-danger and water-balance metrics yielded the best combination of calibration accuracy and predictive skill in modeling annual area burned. The strength of fire-climate relationships varied markedly at multi-decadal scales, with models explaining < 40% to 88% of the variation in annual area burned. The early 20th century (1902-1942) and the most recent two decades (1985-2008) exhibited strong fire-climate relationships, with weaker relationships for much of the mid 20th century (1943-1984), coincident with diminished burning, less fire-conducive climate, and the initiation of modern fire fighting. Area burned and the strength of fire-climate relationships increased sharply in the mid 1980s, associated with increased temperatures and longer potential fire seasons. Unlike decades with high burning in the early 20th century, models developed using fire-climate relationships from recent decades overpredicted area burned when applied to earlier periods. This amplified response of fire to climate is a signature of altered fire-climate-relationships, and it implicates non-climatic factors in this recent shift. Changes in fuel structure and availability following 40+ yr of unusually low fire activity, and possibly land use, may have resulted in increased fire vulnerability beyond expectations from climatic factors alone. Our results highlight the potential for non-climatic factors to alter fire-climate relationships, and the need to account for such dynamics, through adaptable statistical or processes-based models, for accurately predicting future fire activity.
Changing climatic conditions are influencing large wildfire frequency, a globally widespread disturbance that affects both human and natural systems. Understanding how climate change, population growth, and development patterns will affect the area burned by and emissions from wildfires - and how populations will in turn be exposed to emissions - is critical for climate change adaptation and mitigation planning. We quantified the effects of a range of population growth and development patterns in California on emission projections from large wildfires under six future climate scenarios. Here we show that end-of-century wildfire emissions are projected to increase by 19-101% (median increase 56%) above the baseline period (1961-1990) in California for a medium-high temperature scenario, with the largest emissions increases concentrated in Northern California. In contrast to other measures of wildfire impacts previously studied (e.g., structural loss), projected population growth and development patterns are unlikely to substantially influence the amount of projected statewide wildfire emissions. However, increases in wildfire emissions due to climate change may have detrimental impacts on air quality and-combined with a growing population-may result in increased population exposure to unhealthy air pollutants.
We explore the large spatial variation in the relationship between population density and burned area, using continental-scale Geographically Weighted Regression (GWR) based on 13 years of satellite-derived burned area maps from the global fire emissions database (GFED) and the human population density from the gridded population of the world (GPW 2005). Significant relationships are observed over 51.5% of the global land area, and the area affected varies from continent to continent: population density has a significant impact on fire over most of Asia and Africa but is important in explaining fire over < 22% of Europe and Australia. Increasing population density is associated with both increased and decreased in fire. The nature of the relationship depends on land-use: increasing population density is associated with increased burned are in rangelands but with decreased burned area in croplands. Overall, the relationship between population density and burned area is non-monotonic: burned area initially increases with population density and then decreases when population density exceeds a threshold. These thresholds vary regionally. Our study contributes to improved understanding of how human activities relate to burned area, and should contribute to a better estimate of atmospheric emissions from biomass burning.
Wildfires in the United States can be destructive to human life and property. The ability to predict fire danger helps reduce the risks associated with wildfires by keeping firefighters on high alert and allowing better preparedness. In the state of Oklahoma, fire is a common occurrence. By looking at past wildfire records and researching the weather conditions under which they burned, we were able to determine the most important weather conditions affecting wildfire size. We looked at 10 different weather variables and found that minimum relative humidity (r = 0.9, P = 0.001), maximum and average wind speed (r = 0.95, P = 0.003; r = 0.95, P = 0.004 respectively), and precipitation (r = 0.88, P = 0.02) were the most important factors relating to wildfire size. Temperature variables did not have significant relationships with wildfire size. Additionally, we found that most of the largest wildfires occurred in January and December. This information can be used to adjust and improve current wildfire danger models and predictive abilities. We define conditions under which firefighters should be on high alert with hopes of improving their ability to expediently manage rangeland wildfires.
During the summer of 1910 large wildfires occurred throughout the western United States, and especially in the Northern Rocky Mountains. The “Great Idaho Fires” of 1910, alone burned about three million acres (~1.2 Mha)—an area that is approximately the size of Connecticut. Multiple fires ignited and coalesced, burning in forests of northern Idaho and western Montana including parts of the Bitterroot, Cabinet, Clearwater, Coeur d'Alene, Flathead, Kaniksu, Kootenai, Lewis and Clark, Lolo, and St. Joe National Forests. The firestorm burned for days in late August of 1910 and killed 87 people, including 78 firefighters. It is believed to be the largest, although not the deadliest, wildfire complex in recorded U.S. history. Here we show that highly anomalous weather preceded the conflagration in much of the West, including the occurrence of the warmest March on record for the contiguous United States (except March 2012). While the occurrence of very high winds greatly contributed to fast spread of the wildfire, the preceding highly anomalous warm and dry condition since the spring of 1910 likely also contributed to the magnitude of this event. Improved understanding of extreme wildfire outbreaks and climatological conditions associated with them is increasingly important, as such events are increasing in frequency as global and regional warming continues.
A Large Fire Database (LFDB), which includes information on fire location, start date, final size, cause, and suppression action, has been developed for all fires larger than 200 ha in area for Canada for the 1959-1997 period. The LFDB represents only 3.1% of the total number of Canadian fires during this period, the remaining 96.9% of fires being suppressed while <200 ha in size, yet accounts for ∼97% of the total area burned, allowing a spatial and temporal analysis of recent Canadian landscape-scale fire impacts. On average ∼2 million ha burned annually in these large fires, although more than 7 million ha burned in some years. Ecozones in the boreal and taiga regions experienced the greatest areas burned, with an average of 0.7% of the forested land burning annually. Lightning fires predominate in northern Canada, accounting for 80% of the total LFDB area burned. Large fires, although small in number, contribute substantially to area burned, most particularly in the boreal and taiga regions. The Canadian fire season runs from late April through August, with most of the area burned occurring in June and July due primarily to lightning fire activity in northern Canada. Close to 50% of the area burned in Canada is the result of fires that are not actioned due to their remote location, low values-at-risk, and efforts to accommodate the natural role of fire in these ecosystems. The LFDB is updated annually and is being expanded back in time to permit a more thorough analysis of long-term trends in Canadian fire activity.
We evaluated agreement in the location and occurrence of 20th century fires recorded in digital fire atlases with those inferred from fire scars that we collected systematically at one site in Idaho and from existing fire-scar reconstructions at four sites in Washington. Fire perimeters were similar for two of three 20th century fires in Idaho (1924 and 1986). Overall spatial agreement was best in 1924 (producers accuracy = 94% and 68% and users accuracy = 90% and 70% for the 1924 and 1986 fires, respectively). In 1924, fire extent from the atlas was greater than for fire scars, but the reverse was true for 1986. In 1986, fire extent interpreted from the delta normalized burn ratio derived from pre- and post-fire satellite imagery was similar to that inferred from the fire-scar record (producers accuracy = 92%, users accuracy = 88%). In contrast, agreement between fire-scar and fire-atlas records was poor at the Washington sites. Fire atlases are the most readily available source of information on the extent of late 20th century fires and the only source for the early 20th century. While fire atlases capture broad patterns useful at the regional scale, they should be field validated and used with caution at the local scale.
(1) We investigate the impact of climate change on wildfire activity and carbonaceous aerosol concentrations in the western United States. We regress observed area burned onto observed meteorological fields and fire indices from the Canadian Fire Weather Index system and find that May-October mean temperature and fuel moisture explain 24-57% of the variance in annual area burned in this region. Applying meteorological fields calculated by a general circulation model (GCM) to our regression model, we show that increases in temperature cause annual mean area burned in the western United States to increase by 54% by the 2050s relative to the present day. Changes in area burned are ecosystem dependent, with the forests of the Pacific Northwest and Rocky Mountains experiencing the greatest increases of 78 and 175%, respectively. Increased area burned results in near doubling of wildfire carbonaceous aerosol emissions by midcentury. Using a chemical transport model driven by meteorology from the same GCM, we calculate that climate change will increase summertime organic carbon (OC) aerosol concentrations over the western United States by 40% and elemental carbon (EC) concentrations by 20% from 2000 to 2050. Most of this increase (75% for OC and 95% for EC) is caused by larger wildfire emissions with the rest caused by changes in meteorology and for OC by increased monoterpene emissions in a warmer climate. Such an increase in carbonaceous aerosol would have important consequences for western U.S. air quality and visibility.
Although grassland and savanna occupy only a quarter of the world's vegetation, burning in these ecosystems accounts for roughly half the global carbon emissions from fire. However, the processes that govern changes in grassland burning are poorly understood, particularly on time scales beyond satellite records. We analyzed microcharcoal, sediments, and geochemistry in a high-resolution marine sediment core off Namibia to identify the processes that have controlled biomass burning in southern African grassland ecosystems under large, multimillennial-scale climate changes. Six fire cycles occurred during the past 170,000 y in southern Africa that correspond both in timing and magnitude to the precessional forcing of north-south shifts in the Intertropical Convergence Zone. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, we found that wetter and cooler climates cause increased burning in the study region, owing to a shift in rainfall amount and seasonality (and thus vegetation flammability). We also show that charcoal morphology (i.e., the particle's length-to-width ratio) can be used to reconstruct changes in fire activity as well as biome shifts over time. Our results provide essential context for understanding current and future grassland-fire dynamics and their associated carbon emissions.
Steep decline in forest fires about a century ago occurred in coniferous forests over large areas in North America and Fennoscandia. This poorly understood phenomenon has been explained by different factors in different regions. The objective of this study is to evaluate the validity of the four most commonly suggested causes of the decrease in forest fires: fire fighting, over-grazing, climate change and human influence. I compiled the available dendrochronological data and estimated the annually burned proportions of Pinus-dominated forests in four subcontinental regions during the past 500 years. These data were compared to the development of fire suppression, grazing pressure, climate and human livelihoods. The annually burned proportions declined over 90% in all studied regions. In three out of the four regions fires decreased decades before fire suppression began. Available drought data are annually well correlated with fires but could not explain the decrease of the level in annually burned areas. A rapid increase in the number of livestock occurred at the same time with the decrease in fires in the Western US but not in Fennoscandia. Hence, fire suppression in Central Fennoscandia and over-grazing in the Western US may have locally contributed to the reduction of burned areas. More general explanation is offered by human influence hypothesis: the majority of the past forest fires were probably caused by humans and the decrease in the annually burned areas was because of a decrease in human caused fires. This is in accordance with the old written records and forest fire statistics. The decrease in annually burned areas, both in Fennoscandia and the United States coincides with an economic and cultural transition from traditional livelihoods that are associated with high fire use to modern agriculture and forestry.
There has been considerable interest in the recent literature regarding the assessment of post-fire effects on forested areas within the North American boreal forest. Assessing the physical and ecological effects of fire in boreal forests has far-reaching implications for a variety of ecosystem processes – such as post-fire forest succession – and land management decisions. The present paper reviews past assessments and the studies presented in this special issue that have largely been based on the Composite Burn Index and differenced Normalized Burn Ratio (dNBR). Results from relating and mapping fire/burn severity within the boreal region have been variable, and are likely attributed, in part, to the wide variability in vegetation and terrain conditions that are characteristic of the region. Satellite remote sensing of post-fire effects alone without proper field calibration should be avoided. A sampling approach combining field and image values of burn condition is necessary for successful mapping of fire/burn severity. Satellite-based assessments of fire/burn severity, and in particular dNBR and related indices, need to be used judiciously and assessed for appropriateness based on the users’ need. Issues unique to high latitudes also need to be considered when using satellite-derived information in the boreal forest region.
Humans and their ancestors are unique in being a fire-making species, but ‘natural’ (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from ‘natural’ background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.
The factors controlling the extent of fire in Africa south of the equator were investigated using moderate resolution (500 m) satellite-derived burned area maps and spatial data on the environmental factors thought to affect burnt area. A random forest regression tree procedure was used to determine the relative importance of each factor in explaining the burned area fraction and to address hypotheses concerned with human and climatic influences on the drivers of burnt area. The model explained 68% of the variance in burnt area. Tree cover, rainfall in the previous 2 years, and rainfall seasonality were the most important predictors. Human activities – represented by grazing, roads per unit area, population density, and cultivation fraction – were also shown to affect burnt area, but only in parts of the continent with specific climatic conditions, and often in ways counter to the prevailing wisdom that more human activity leads to more fire. The analysis found no indication that ignitions were limiting total burnt area on the continent, and most of the spatial variation was due to variation in fuel load and moisture. Split conditions from the regression tree identified (i) low rainfall regions, where fire is rare; (ii) regions where fire is under human control; and (iii) higher rainfall regions where burnt area is determined by rainfall seasonality. This study provides insights into the physical, climatic, and human drivers of fire and their relative importance across southern Africa, and represents the beginnings of a predictive framework for burnt area.
Large wildfire occurrence and burned area are modeled using hydroclimate and landsurface characteristics under a range of future climate and development scenarios. The range of uncertainty for future wildfire regimes is analyzed over two emissions pathways (the Special Report on Emissions Scenarios [SRES] A2 and B1 scenarios); three global climate models (Centre National de Recherches Météorologiques CM3, Geophysical Fluid Dynamics Laboratory CM2.1 and National Center for Atmospheric Research PCM1); three scenarios for future population growth and development footprint; and two thresholds for defining the wildland-urban interface relative to housing density. Results were assessed for three 30-year time periods centered on 2020, 2050, and 2085, relative to a 30-year reference period centered on 1975. Increases in wildfire burned area are anticipated for most scenarios, although the range of outcomes is large and increases with time. The increase in wildfire burned area associated with the higher emissions pathway (SRES A2) is substantial, with increases statewide ranging from 36% to 74% by 2085, and increases exceeding 100% in much of the forested areas of Northern California in every SRES A2 scenario by 2085.
We estimated the impact of climatic change on wildland fire and suppression effectiveness in northern California by linking
general circulation model output to local weather and fire records and projecting fire outcomes with an initial-attack suppression
model. The warmer and windier conditions corresponding to a 2 × CO2 climate scenario produced fires that burned more intensely and spread faster in most locations. Despite enhancement of fire
suppression efforts, the number of escaped fires (those exceeding initial containment limits) increased 51% in the south San
Francisco Bay area, 125% in the Sierra Nevada, and did not change on the north coast. Changes in area burned by contained
fires were 41%, 41% and –8%, respectively. When interpolated to most of northern California's wildlands, these results translate
to an average annual increase of 114 escapes (a doubling of the current frequency) and an additional 5,000 hectares (a 50%
increase) burned by contained fires. On average, the fire return intervals in grass and brush vegetation types were cut in
half. The estimates reported represent a minimum expected change, or best-case forecast. In addition to the increased suppression costs and economic damages, changes in fire
severity of this magnitude would have widespread impacts on vegetation distribution, forest condition, and carbon storage,
and greatly increase the risk to property, natural resources and human life.
Background: In late October 2003, a series of wildfires exposed urban populations in Southern California to elevated levels of air pollution over several weeks. Previous research suggests that short-term hospital admissions for respiratory outcomes increased specifically as a result of these fires.
Objective: We assessed the impact of a wildfire event during pregnancy on birth weight among term infants.
Methods: Using records for singleton term births delivered to mothers residing in California’s South Coast Air Basin (SoCAB) during 2001–2005 (n = 886,034), we compared birth weights from pregnancies that took place entirely before or after the wildfire event (n = 747,590) with those where wildfires occurred during the first (n = 60,270), second (n = 39,435), or third (n = 38,739) trimester. The trimester-specific effects of wildfire exposure were estimated using a fixed-effects regression model with several maternal characteristics included as covariates.
Results: Compared with pregnancies before and after the wildfires, mean birth weight was estimated to be 7.0 g lower [95% confidence interval (CI): –11.8, –2.2] when the wildfire occurred during the third trimester, 9.7 g lower when it occurred during the second trimester (95% CI: –14.5, –4.8), and 3.3 g lower when it occurred during the first trimester (95% CI: –7.2, 0.6).
Conclusions: Pregnancy during the 2003 Southern California wildfires was associated with slightly reduced average birth weight among infants exposed in utero. The extent and increasing frequency of wildfire events may have implications for infant health and development.
Fire frequency, extent, and size exhibit a strong linkage with climate conditions and play a vital role in the climate system. Previous studies have shown that the frequency of large fires in the western United States increased significantly since the mid-1980s due to climate warming and frequent droughts. However, less work has been conducted to examine burned area and fire emissions of large fires at a national scale, and the underlying mechanisms accounting for the increases in the frequency of large fires are far from clear. In this study, we integrated remote-sensed fire perimeter and burn severity data sets into the Dynamic Land Ecosystem Model to estimate carbon emissions from large fires (i.e., fires with size larger than 1000acres or 4.05km2) in conterminous United States from 1984 to 2012. The results show that average area burned by large fires was 1.44×104km2yr-1 and carbon emissions from large fires were 17.65TgCyr-1 during the study period. According to the Mann-Kendall trend test, annual burned area and pyrogenic carbon emissions presented significant upward trends at the rates of 810km2yr-1 and 0.87TgCyr-1, respectively. Characteristic fire size (fire size with the largest contribution to the total burned area) in the period of 2004-2012 increased by 176.1% compared to the period of 1984-1993. We further found that the larger fires were associated with higher burn severity and occurred more frequently in the warmer and drier conditions. This finding implies that the continued warming and drying trends in the 21st century would enhance the total burned area and fire emissions due to the contributions of larger and more severe wildfires.
What makes a good clinical study may not be the source of a discovery that propells a medical breakthrough, but getting to to innovation may require other ways of collaboration and investigation melding ideas from many disciplines as has been highlighted in this Future of Medicine series of Viewpoints.Biomedical research is clearly blossoming in terms of accumulated data, evolving technologies, and published articles. The pace of growth has been rapid and can seem vertiginous at times. This issue of JAMA concludes a 9-month series of stimulating Viewpoints on the theme of Scientific Discovery and the Future of Medicine.1 The richness of the ideas that have been summarized by brilliant, world-caliber investigators deserves attention and acknowledgment. However, few advances in biomedical science materialize into human applications that affect health; even when successful, the translation sometimes takes several decades.2,3 Thus, a tantalizing question remains: which of the most promising ideas will soon prove to be most important, translatable, and life saving? Is it possible to identify a major scientific discovery when first reported?
Natural and human systems are increasingly affected by climate change. A synopsis of the documentation of scientific evidence for the observed effects of climate change in the third, fourth and fifth assessment reports of the Intergovernmental Panel on Climate Change shows that the amount of evidence available, the range of impacts observed and their geographical scope has expanded rapidly. Fifteen years ago, robust evidence for observed climate change impacts was almost exclusively available for the cryosphere and terrestrial ecosystems in mid to high northern latitudes or mountain regions. By contrast, the effects of climate change are now documented for all land areas and oceans, for both natural and human systems. Over the last decade, evidence has increased especially for impacts on marine ecosystems, food production and wildfire regimes. No recent progress has been found in the documentation of impacts of climate change related sea level rise. Though the evidence base has improved substantially for regions in the Southern hemisphere and developing countries, the global distribution of observed impacts remains uneven.
"Denis Rancourt has turned the entire notion of RACISM on its head and at the same time exposes racist acts committed by others to deflect that characterization from sticking at the highest levels of The Academy. North American civil rights defenders need this book at this time. Rancourt’s deeply incisive Fight Against Racism brings us back to the reality of the struggle, away from the manoeuvring for class advantage and away from the victim’s desire to create illusions of state-given justice."—Cynthia McKinney, First African-American woman elected to represent Georgia in the US Congressional House of Representatives
The Interdecadal Pacific Oscillation (IPO) influences multidecadal drought risk across the Pacific, but there are no millennial-length, high resolution IPO reconstructions for quantifying long-term drought risk. In Australia, drought risk increases in positive phases of the IPO, yet few suitable rainfall proxies and short (~100 y) instrumental records mean large uncertainties remain around drought frequency and duration. Likewise, it is unknown whether mega-droughts have occurred in Australia's past. In this study, an atmospheric teleconnection in the Indian Ocean mid-latitudes linking East Antarctica and Australia is exploited to produce the first accurate, annually dated millennial-length IPO reconstruction from the Law Dome (East Antarctica) ice core. Combined with an eastern Australian rainfall proxy from Law Dome, the first millennial-length Australian mega-drought (>5 y duration) reconstruction is presented. Eight mega-droughts are identified including one 39 y drought (AD 1174–1212), which occurred during an unprecedented century of aridity (AD 1102–1212).
We used a database capturing large wildfires (> 405 ha) in the western US to document regional trends in fire occurrence, total fire area, fire size, and day of year of ignition (DOY) for 1984-2011. Over the western US and in a majority of ecoregions, we found significant, increasing trends in the number of large fires and/or total large fire area per year. Trends were most significant for southern and mountain ecoregions, coinciding with trends towards increased drought severity. For all ecoregions combined, the number of large fires increased at a rate of seven fires per year while total fire area increased at a rate of 355 km2 per year. Continuing changes in climate, invasive species, and consequences of past fire suppression, added to the impacts of larger, more frequent fires, will drive further disruptions to fire regimes of the western US and other fire-prone regions of the world.
These experiments point to a cholesterol dependent mechanism for controlling recep- tor function. As hematopoietic growth factor receptors in stem cells organize in membrane rafts, the availability of cholesterol for raft for- mation modulates receptor function. Mem- brane
A high-resolution black carbon (BC) record from 27.5 kyr BP to present was reconstructed using a chemical oxidation method on loess and paleosol samples from the Lijiayuan section of the Chinese Loess Plateau. The black carbon mass sedimentation rates (BCMSR) and carbon isotopic record reveal a paleofire history and its relationship with climate and vegetation changes at the study site. The BCMSR record was decomposed into two components: background BCMSR and the BCMSR peaks. The background BCMSR represents regional fires and shows high fire activities occurred contemporaneous with the Younger Dryas, Older Dryas, Heinrich events and Greenland stadials as registered in the loess grain size record. This suggests a rapid response of regional fires on the Loess Plateau to abrupt climate changes. Spectral analysis of background BCMSR showed two meaningful periodicities of 1620 and 1040 years, close to the cyclicity of the East Asian monsoon as recorded in the stalagmite δ18O record in Central China. This indicates a tight control of millennial scale wet–dry changes in the monsoonal climate on regional fires on the Loess Plateau. By contrast, the BCMSR peaks are considered to reflect local fire episodes. The occurrences of local fires were more frequent during the last glacial period, with a maximum frequency of ~ 6 episodes/1000 years during the Last Glacial Maximum (LGM) (22.3 to 14.6 kyr BP), when the climate was drier and more continuous grassy fuels existed on the landscape. During the last glacial–interglacial transition (LGIT) period (14.6 to 11.0 kyr BP), fire frequency was largely reduced due to an increase in precipitation and more woody vegetation. If the LGIT period is taken as an analog for the projected near future, then future global warming alone may not produce large wildfires in northwestern China. Wildfires remained infrequent during the early-to-middle Holocene. Biomass burning increased after 4.0 kyr BP, when the climate became drier and land-use was more intensive. BC carbon isotope ratios may well reflect changes in the vegetation being burnt (i.e., grasses versus trees), yielding results consistent with the associated pollen data in the region.
Satellite fire products have the potential to construct inter-annual time series of fire activity, but estimating area burned requires considering biases introduced by orbiting geometry, fire behavior, and the presence of clouds and smoke. Here we evaluated the performance of fire counts from the Advanced Thermal Scanning Radiometer (ATSR) for the boreal forest region using area burned information from other sources. We found ATSR detection rate varied between regions and different years, being higher during large fire years than during small fire years. The results show ATSR fire counts do not represent an unbiased sample of fire activity, and independent validation may be required prior to using this data set in studies of global emissions from biomass burning.
A century of wildfire suppression in the United States has led to increased fuel loading and large-scale ecological change across some of the nation's forests. Land management agencies have responded by increasing the use of prescribed fire and thinning. However, given the continued emphasis on fire suppression, current levels of funding for such fuel management practices are unlikely to maintain the status quo, let alone reverse the effects of fire exclusion. We suggest an alternative approach to wildfire management, one that places less emphasis on suppression and instead encourages managers to balance short-term wildfire damages against the long-term consequences of fire exclusion. However, any major change in wildfire management, such as the one proposed here, will shift the costs and benefits of wildfire management, inevitably raising opposition.
Vegetation fires remain as one of the most important processes governing land use and land cover change in tropical areas. The large area extent of fire prone areas associated with human activities makes satellite remote sensing of active fires a valuable tool to help monitor biomass burning in those regions. However, identification of active fire fronts under optically thick clouds is not possible through passive remote sensing, often resulting in omission errors. Previous analyses of fire activity either ignored the cloud obscuration problem or applied corrections based on the assumption that fire occurrence is not impacted by the presence of clouds. In this study we addressed the cloud obscuration problem in the Brazilian Amazon region using a pixel based probabilistic approach, using information on previous fire occurrence, precipitation and land use. We implemented the methodology using data from the geostationary GOES imager, covering the entire diurnal cycle of fire activity and cloud occurrence. Our assessment of the method indicated that the cloud adjustment reproduced the number of potential fires missed within 1.5% and 5% of the true fire counts on annual and monthly bases respectively. Spatially explicit comparison with high resolution burn scar maps in Acre state showed a reduction of omission error (from 58.3% to 43.7%) and only slight increase of commission error (from 6.4% to 8.8%) compared to uncorrected fire counts. A basin-wide analysis of corrected GOES fire counts during 2005 showed a mean cloud adjustment factor of approximately 11%, ranging from negligible adjustment in the central and western part of the Brazilian Amazon to as high as 50% in parts of Roraima, Para and Mato Grosso.