Variations In Fire Activity Research Articles

Ecological and climatic controls of modern wildfire activity patterns across southwestern South America

Understanding how patterns of wildfire activity across biomes are shaped by heterogeneity in biomass resources to burn and atmospheric conditions conducive to burning is a high research priority in the context of global environmental change. Along a latitudinal gradient (25 to 56° S) from semi‐arid scrublands through Mediterranean‐type vegetation to wet forests in southwestern South America (SSA) we analyzed influences of mean climate and interannual climate variability on fire activity using documentary fire records from 1984 to 2008. We identified large regions with common temporal variability in annual area burned, related this variability to local interannual climate variability and in turn to modes of the major tropical and extratropical climate drivers of the southern hemisphere—El Niño‐Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO). Differences in fire activity response to interannual climate variability were related to the relative influences of available biomass to burn, and to weather effects on amounts of fine fuels and fuel moisture conditions. The pattern of average fire activity along this latitudinal moisture/productivity gradient corresponds well with the varying constraints model. This model predicts low fire activity towards the arid extreme due to reduced burnable biomass and again towards the humid extreme due to infrequent weather suitable for drying fuels, and predicts a broad zone of high fire activity at intermediate locations where resources to burn are abundant in all years and fuel moisture dries under reliably dry summer conditions. The dominant influence on interannual climate variability is AAO, which explained most of the variability in fire activity both by reducing seasonal precipitation in mesic and wet forests where fire is dependent on infrequent drought and by enhancing fine fuel production in Mediterranean‐type vegetation where fuel amount and continuity constrain fire activity. In the context of the drying and warming trends in SSA related to the continued positive anomaly in AAO, our results underscore the importance of the varying constraints on fire activity and modulation of fire‐climate relationships by different vegetation types, which is a much needed step toward developing fire projections under future climate.

El Niño and health risks from landscape fire emissions in Southeast Asia.

Emissions from landscape fires affect both climate and air quality1. In this study, we combine satellite-derived fire estimates and atmospheric modeling to quantify health effects from fire emissions in Southeast Asia from 1997 to 2006. This region has large interannual variability in fire activity due to coupling between El Niño-induced droughts and anthropogenic land use change2,3. We show that during strong El Niño years, fires contribute up to 200 μg/m3 and 50 ppb in annual average fine particulate matter (PM2.5) and ozone (O3) surface concentrations near fire sources, respectively. This corresponds to a fire contribution of 200 additional days per year that exceed the World Health Organization (WHO) 50 μg/m3 24-hour PM2.5 interim target (IT-2)4 and an estimated 10,800 (6,800–14,300) person (~2%) annual increase in regional adult cardiovascular mortality. Our results indicate that reducing regional deforestation and degradation fires would improve public health along with widely established benefits from reducing carbon emissions, preserving biodiversity, and maintaining ecosystem services.

024 Experimental approaches to understanding the flammability of ancient ecosystems : a case study of variations in fire activity across the Triassic-Jurassic boundary event

024 Experimental approaches to understanding the flammability of ancient ecosystems : a case study of variations in fire activity across the Triassic-Jurassic boundary event

Inter- and intra-annual profiles of fire regimes in the managed forests of Canada and implications for resource sharing

Year-to-year variation in fire activity in Canada constitutes a key challenge for fire management agencies. Interagency sharing of fire management resources has been ongoing on regional, national and international scales in Canada for several decades to better cope with peaks in resource demand. Inherent stressors on these schemes determined by the fire regimes in constituent jurisdictions are not well known, nor described by averages. We developed a statistical framework to examine the likelihood of regional synchrony of peaks in fire activity at a timescale of 1 week. Year-to-year variations in important fire regime variables and 48 regions in Canada are quantified by a joint distribution and profiled at the Provincial or Territorial level. The fire regime variables capture the timing of the fire season, the average number of fires, area burned, and the timing and extent of annual maxima. The onset of the fire season was strongly correlated with latitude and longitude. Regional synchrony in the timing of the maximum burned area within fire seasons delineates opportunities for and limitations to sharing of fire suppression resources during periods of stress that were quantified in Monte Carlo simulations from the joint distribution.

Reconstructing annual area burned in the northern Rockies, USA: AD 1626-2008

We used a tree-ring chronology as a proxy for annual area burned (AAB) in the northern Rockies, USA during AD 1626–2008. We correlated annual ring widths of alpine larch trees (Larex lyallii) sampled at a single high-elevation site in western Montana with AAB for the United States Forest Region 1. Radial growth was significantly associated with AAB (R2 = 0.35, p < 0.001), demonstrating the potential to use high-elevation conifers as markers of interannual variations in fire activity. The results suggest that the period 1929–1945 would have been the most active since the early 1600s had not extensive fire suppression and harvest activities altered the fire regime. Comparisons of the predicted values of area burned to a century-long fire atlas were significant for both the entire record (rs = 0.333, p < 0.01) and reconstruction period (rs = 0.645 p < 0.001). Similarly, predicted AAB was significantly correlated (r = 0.230) to fire-scar data during 1650–1900. These results suggest the feasibility of using tree-ring chronologies as an additional measure of fire activity, particularly as they allow an assessment and comparison of fire activity during centuries with and without fire suppression and harvest activities.

Top-Down and Bottom-Up Controls on Fire Regimes Along an Elevational Gradient on the East Slope of the Sierra Nevada, California, USA

Fire is an ecologically significant process in the fire-prone ponderosa pine and mixed conifer forests of the northern Sierra Nevada. Fire regimes are influenced by processes that operate over a range of scales that can be grouped broadly as bottom-up (e.g., topography, forest type) or top-down (e.g., climate variation, human land use) controls. To identify the bottom-up versus top-down controls on fire regimes, we quantified spatial and temporal variation in fire occurrence and extent using fire-scar dendrochronology. Inter-annual climate variability and human land use patterns strongly influenced fire regimes. Years of widespread burning and fire-free years were associated with dry and wet years, respectively. Variation in fire activity was also associated with variation in the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Widespread burning occurred during La Nina years (cool ENSO) and during positive conditions of the PDO (warm PDO). Fire occurrence declined with Euro-American settlement in the nineteenth century and only two fires were recorded in the study area after 1905, the date fire suppression was implemented. Fire regimes were also influenced by bottom-up controls. Fire return intervals (FRI) were shorter in pine-dominated low-elevation forests than in high-elevation fir-dominated mixed conifer forests, although FRI did not vary by slope aspect.

Decadal dynamics of tree cover in an Australian tropical savanna

AbstractSpatio‐temporal variation in tropical savanna tree cover remains poorly understood. We aimed to quantify the drivers of tree cover in tropical mesic savannas in Kakadu National Park by relating changes in tree cover over 40 years to: mean annual rainfall, fire activity, initial tree cover and prior changes in tree cover. Aerial photography, acquired in 1964, 1984 and 2004, was obtained for fifty sites in Kakadu that spanned a rainfall gradient from approximately 1200 to 1600 mm. The remotely sensed estimates of tree cover were validated via field survey. Linear mixed effects modelling and multi‐model inference were used to assess the strength and form of the relationships between tree cover and predictor variables. Over the 40 years, tree cover across these savannas increased on average by 4.94 ± 0.88%, but was spatio‐temporally variable. Tree cover showed a positive albeit weak trend across the rainfall gradient. The strength of this positive relationship varied over the three measurement times, and this suggests that other factors are important in controlling tree cover. Tree cover was positively related to prior tree cover, and negatively correlated with fire activity. Over 20 years tree cover was more likely to increase if (i) tree cover was initially low or (ii) had decreased in the previous 20‐year interval or (iii) there had been fewer fires. Across the examined rainfall gradient, the greater variability in fire activity and inherently higher average tree cover at the wetter latitudes resulted in greater dynamism of tree cover compared with the drier latitudes. This is consistent with savanna tree cover being determined by interactions between mean annual rainfall, tree competition and frequent fire in these tropical mesic savannas.

Temporal and spatial variability in biomass burned areas across the USA derived from the GOES fire product

Burned area is a critical input to the algorithms of biomass burning emissions and understanding variability in fire activity due to climate change but it is difficult to estimate. This study presents a robust algorithm to reconstruct the patterns in burned areas across Contiguous United States (CONUS) in diurnal, seasonal, and interannual scales from 2000–2006. Specifically, burned areas in individual fire pixels are empirically calculated using diurnal variations in instantaneous fire sizes from the Geostationary Operational Environmental Satellites (GOES) WF_ABBA (Wildfire Automated Biomass Burning Algorithm) fire product. GOES burned areas exhibit diurnal variability with a temporal scale of half hours. The cumulative burned area during 9:00–16:00 local solar time accounts for 65%–81% of the total daily burned area. The diurnal variability is strongest in croplands compared to shrublands, grasslands, savannas, and forests. Analysis on a seasonal scale indicates that over 56% of burning occurs during summer (June–August). On average, the total annual burned area during the last seven years is 2.12 × 10 4 ± 0.41 × 10 4 km 2. The algorithm developed in this study can be applied to obtain burned area from the detections of GOES active fires at near real time, which can greatly improve the estimates of biomass burning emissions needed for predicting air quality.

Future Area Burned in Canada

Historical relationships between weather, the Canadian fire weather index (FWI) system components and area burned in Canadian ecozones were analysed on a monthly basis in tandem with output from the Canadian and the Hadley Centre GCMs to project future area burned. Temperature and fuel moisture were the variables best related to historical monthly area burned with 36-64% of the variance explained depending on ecozone. Our results suggest significant increases in future area burned although there are large regional variations in fire activity. This was especially true for the Canadian GCM where some ecozones show little change in area burned, however area burned was not projected to decrease in any of the ecozones modelled. On average, area burned in Canada is projected to increase by 74-118% by the end of this century in a 3 × CO2 scenario. These estimates do not explicitly take into account any changes in vegetation, ignitions, fire season length, and human activity (fire management and land use activities) that may influence area burned. However, the estimated increases in area burned would have significant ecological, economic and social impacts for Canada.

Characterization of the spatio‐temporal patterns of global fire activity using satellite imagery for the period April 1992 to March 1993

Summary Aim This paper describes the characteristics of the spatio‐temporal distribution of vegetation fires as detected from satellite data for the 12 months April 1992 to March 1993. Location Fires are detected daily at a spatial resolution of 1 km for all land areas of the globe. Methods From the fire location information a daily gridded product at 0.5° by 0.5° has been constructed. Two methods of characterizing the spatio‐temporal pattern of vegetation fires are discussed. The first applies empirical orthogonal function analysis to the monthly series of gridded data. The second approach defines and extracts a number of spatial and temporal parameters from the gridded product. The descriptive parameters extracted are used in a cluster analysis in order to group cells with similar characteristics into a small number of classes. Results Using daily global satellite observations, it is possible to characterize the spatial and temporal variability in fire activity. Most of this variability is within the tropical belt, where the majority of fire activity is concentrated, nonetheless fire was also detected in temperate and boreal regions. The period in which fire occurred varied from region to region. Parameterization provided a very synthetic view of this variability facilitating regional intercomparison. Clustering identifies five classes of fire activity, each of which can be associated with particular climatic conditions, vegetation types and land‐use. Main conclusions Global monitoring of vegetation fire from satellite is possible. The analysis provides a coherent, consistent and synoptic view of global fire activty with one data set. The type of information extracted can be of use in global atmospheric chemistry modelling and for studying the role of fire in relation to global change issues.

An overview of GOES‐8 diurnal fire and smoke results for SCAR‐B and 1995 fire season in South America

The launch of the eighth Geostationary Operational Environmental Satellite (GOES‐8) in 1994 introduced an improved capability for diurnal fire and smoke monitoring throughout the western hemisphere. In South America the GOES‐8 automated biomass burning algorithm (ABBA) and the automated smoke/aerosol detection algorithm (ASADA) are being used to monitor biomass burning. This paper outlines GOES‐8 ABBA and ASADA development activities and summarizes results for the Smoke, Clouds, and Radiation in Brazil (SCAR‐B) experiment and the 1995 fire season. GOES‐8 ABBA results document the diurnal, spatial, and seasonal variability in fire activity throughout South America. A validation exercise compares GOES‐8 ABBA results with ground truth measurements for two SCAR‐B prescribed burns. GOES‐8 ASADA aerosol coverage and derived albedo results provide an overview of the extent of daily and seasonal smoke coverage and relative intensities. Day‐to‐day variability in smoke extent closely tracks fluctuations in fire activity.

Remote sensing of bush fire dynamics in Central Africa from 1984 to 1988: analysis in relation to regional vegetation and pluviometric patterns

Spatial and temporal subcontinental patterns of fire distribution in Africa, may vary strongly from year to year. These variations may be of climatic or anthropic origin. Global Area Coverage (GAC) data, from the Advanced Very High Resolution Radiometer (AVHRR), are known both to provide a good description of fire calendar and on a continental scale, a good indicator of locations of intense fire activity. In fact, the GAC data, available on a daily basis back to July 1981, is the only source of information actually available to determine burning patterns both on a continental scale and over long periods of time. This study presents the spatio-temporal distribution of vegetation fire in Central Africa, as derived from GAC imagery, over the four 1984/85 to 1987/88 dry seasons of the Northern Hemisphere (November to February periods). The analysis of the mean fire distribution patterns over the four dry seasons, as defined by vegetation cover and pluviometric conditions, shows a north to south gradient of fire activity in the savannah domain: This gradient of fire activity has been previously related to the annual pluviometric calendar and the amount of rainfall. The strong interannual variability in fire activity observed for this four-years-period could not, however, be explained by the monthly pluviometric patterns. The observed fire gradient therefore seems to result from additional meteorological or anthropic parameters. The methodology used in this study demonstrates the potential of GAC data for fire monitoring at a subcontinental scale. Current work is extending the area of interest to the entire African continent using the 10-yr-period of GAC imagery.

The limitations and potential of AVHRR GAC data for continental scale fire studies

Abstract Global Area Coverage (GAC) data from the Advanced Very High Resolution Radiometer (AVHRR) are available on a daily basis, dating back to July 1981. The AVHRR's 3·55–3·93 μm channel is suitable for detection of terrestrial hot spots, such as bushfires. The long-term archives and global cover make the GAC a potentially valuable data source for large scale fire studies. However, these data are sampled spatially through a combination of line skipping and averaging. This study shows that the sampling affects the sensitivity of GAC for fire detection in relation to ecosystem and season. The GAC are found to provide a reasonable measure of fire activity in grassland and open b'ush savannah, but to perform poorly in the forest margins. Overall at least 79 per cent of fires detected with non-sampled AVHRR data are missed by the GAC. This severely limits the use of GAC data for quantitative fire studies. The GAC does appear to provide a reasonable measure of fire calendar (i.e., variations in fire activity...

Fire from space: Global fire evaluation using infrared remote sensing

Abstract Mid-infrared (IR) orbiting platforms are attractive candidates for monitoring fire on a global basis, as needed for global biogeochemical studies. In the mid IR, fires radiate intensely against a low-energy background. Thus fires occupying a fraction of a percent of a pixel can be detected. Fire size and temperature can, in theory, be calculated from multi-channel IR measurements. The fire record in raw IR data is biased by obscuration by clouds and smoke, sensor saturation, difficulties in gaining a representative sample given the diurnal variation in fire activity and the large role played in global fire emissions by cooking fires, charcoal making and very small burns on agricultural wastes. The bias is spatially variant and its nature is poorly understood. Further research and engineering is required before IR sensing can improve upon current rough estimates of biomass burning based on scattered available data.