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.
The area burned in southern Africa during the 2000 dry season was mapped on a monthly basis from May to November using SPOT‐VEGETATION (VGT) satellite imagery at 1 km spatial resolution. Burned areas were identified with a classification tree that relied only on the near‐infrared channel of VGT. The classification tree algorithm yielded very accurate results (Kappa = 0.93). However, when compared with burned area maps derived from 30 m resolution Landsat Enhanced Thematic Mapper (ETM+) imagery, the VGT 1 km burned area maps reveal variable accuracy, dependent on vegetation type and on the spatial pattern of the burned areas. Fire incidence was higher in the northern part of the study area, especially in Wetter Zambezian Miombo Woodland, Mosaic of Guineo‐Congolian Lowland Forest and Secondary Grassland, Edaphic and Secondary Grassland on Kalahari Sand, Drier Zambezian Miombo Woodland, and Undifferentiated North‐Zambezian Miombo Woodland. Fire incidence was lower in the eastern part of the study area and almost absent from the western and southern semiarid and desert regions. The most extensively burned countries were, in decreasing order, the Democratic Republic of Congo, Angola, Mozambique and Zambia. The total area burned was estimated at 959480 km2.
Abstract. Spectral properties of recent burns are characterised, in the visible, near infrared, mid-infrared, thermal infrared, and microwave spectral domains. Fireinduced reflectance changes are also compared for various ecosystems and biomes, and discussed in terms of the ecological effects of phytomass combustion. The spectral signatures of combustion products and of burnt areas are compared with those of various plant material and land cover types, in order to graphically represent relevant aspects of burnt area spectral discrimination. A series of colour composite images, based on Landsat Thematic Mapper data is used to illustrate the appearance of burnt surfaces in various tri-spectral spaces, and in contrast with healthy forests, agricultural fields, and urban areas. The temporal evolution of the spectral properties of burns is also demonstrated, with a five-year time series of Thematic Mapper images of two conifer forest burns in central Portugal. Finally, a series of conclusions is proposed, concerning the distinctive spectral properties of burnt surfaces, and implications for discrimination and mapping of such areas. IntroductionVegetation fires are common in tropical, temperate, and boreal biomes. In the tropics fire is often used as a land management tool, employed in shifting agriculture, hunting practices, to prevent the invasion of grasslands by shrubs, and in the conversion of primary forest to other uses. In temperate regions fire is also extensively used for slash burning, but is most often considered a hazard when it burns in ecosystems that are prized for their economic and ecological value. In both tropical and temperate biomes, a great majority of fires, whether desired or not, occur as a result of human activities, but in boreal regions natural causes (i.e. lightning) still account for a significant proportion of the total area burnt, and fire is a very important ecological factor influencing plant community dynamics.These various kinds of fire activity generate a range of economic, ecological, atmospheric and climatic impacts, with magnitudes that are strongly dependent on the areal extent of the burns. Detailed and current information concerning the location and extent of the burnt areas is important for assessing economic losses and ecological effects, monitoring land use and land cover changes, and modelling E. Chuvieco (ed.), Remote Sensing of Large Wildfires
The extreme 2017 fire season in Portugal led to widespread recognition of the need for a paradigm shift in forest and wildfire management. We focused our study on Alvares, a parish in central Portugal located in a fire-prone area, which had 60% of its area burned in 2017. We evaluated how different fuel treatment strategies may reduce wildfire hazard in Alvares through (i) a fuel break network with different extents corresponding to different levels of priority and (ii) random fuel treatments resulting from a potential increase in stand-level management intensity. To assess this, we developed a stochastic wildfire simulation system (FUNC-SIM) that integrates uncertainties in fuel distribution over the landscape. If the landscape remains unchanged, Alvares will have large burn probabilities in the north, northeast and center-east areas of the parish that are very often associated with high fireline intensities. The different fuel treatment scenarios decreased burned area between 12.1–31.2%, resulting from 1–4.6% increases in the annual treatment area and reduced the likelihood of wildfires larger than 5000 ha by 10–40%. On average, simulated burned area decreased 0.22% per each ha treated, and cost-effectiveness decreased with increasing area treated. Overall, both fuel treatment strategies effectively reduced wildfire hazard and should be part of a larger, holistic and integrated plan to reduce the vulnerability of the Alvares parish to wildfires.
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