1 Spatial Modelling of the Terrestrial Environment - Georeferencial

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9 Estimation of Energy Emissions, Fireline Intensity and Biomass Consumption in Wildland Fires: A Potential Approach Using Remotely Sensed Fire Radiative Energy Martin J. Wooster, G.L.W. Perry, B. Zhukov and D. Oertel 9.1 Introduction Aside from modification of the Earth’s surface for urban development and agricultural activity, fire is the most widespread of all terrestrial disturbance agents (Bond and van Wilgen, 1996), making it a key candidate for observation via remote sensing. Evidence from a variety of sources suggests that fire has been an important feature of the natural environment for at least 350 million years (e.g. Cope and Chaloner, 1985). Furthermore, debates continue over the role of wildfire events in climate change and species extinction at the Cretaceous/Tertiary boundary (Anders et al., 1991; McLean, 1991). Without doubt, fire has influenced terrestrial ecosystems over evolutionary time, but there is now a large body of evidence suggesting that in many, and probably most, geographical regions the majority of wildland fires are now not purely ‘natural’ phenomena, but are ignited by humans, either deliberately or as a result of some related anthropic activity (Saarnak, 2001). Brain and Sillen (1988) suggest that the earliest evidence of the use of fire by hominids is approximately 1.5 million years BP and the rise of humans as a major fire ignition source is one reason why biomass burning is believed to have significantly increased in the last 100 000–250 000 years BP (Caldararo, 2002; Keller et al., 2002). Spatial Modelling of the Terrestrial Environment. Edited by R. Kelly, N. Drake, S. Barr. C○ 2004 John Wiley & Sons, Ltd. ISBN: 0-470-84348-9.
176 Spatial Modelling of the Terrestrial Environment Fires have a range of environmental effects across multiple scales in time and space. For example, fires at the local scale significantly reduce the vegetation cover, and more intense fires may completely remove all above-ground vegetation. At the appropriate time and place such processes maybe advantageous, for example, in rapidly returning nutrients to the soils after grassland senescence, or by keeping forest surface litter levels low so as to reduce the likelihood of larger, more intense fires that may kill normally fire-tolerant vegetation. Furthermore, the reproductive biology of many species in fire-prone systems is closely related to fire activity (Whelan, 1995), with, for example, heat or chemicals in the smoke emitted by the fire triggering flowering and/or seed release (Enright et al., 1997). Additionally, the nutrient-rich post-fire ash bed may be important for the establishment of seedlings in certain systems. However, at the local scale, fires can also alter the species makeup and ecology of an area and render the underlying soils more prone to erosion (Johansen, 2001). In extreme cases dramatically altered fire regimes may cause the local extinction of some species (Keith, 1996), whilst at the regional scale fire may also have significant ecological effects, resulting in altered flows of energy and matter through the landscape and the generation of spatially complex mosaic patterns (Turner et al., 1994, 1997). At these regional scales, the particulates and gases released during burning can concentrate at levels far beyond recognized safe human health limits, leading to hazardous visibility and poor air quality. A high-profile example of regional-scale fire-related pollution occurred during the 1997–1998 fires in SE Asia, when an El Niño-related drought allowed fires to become much more intense and widespread than is normally the case, and which also significantly reduced the incidence of ‘cleaning’ of the atmosphere by rainfall (Wooster and Strub, 2002). The widespread haze blanketed areas of SE Asia for weeks and resulted in regional economic losses of more than $1.4 billion, exposing more than 20 million people to potentially dangerous levels of air pollution (Brown, 1998; Schweithelm, 1998). Such is the magnitude of fire activity on Earth, particularly in the tropics, that pyrogenic gaseous and particulate emissions are now recognized to be highly significant at the global scale, where Earth’s atmospheric chemistry, cloud and rainfall characteristics, and radiative budget are all influenced by the combustion products (Rosenfeld, 1999; Andreae and Merlet, 2001; Chou et al., 2002). Clearly, for the above reasons, biomass burning and pyrogenic emissions must be rigorously considered when analysing the effect of wildfires on Earth’s surface and atmosphere (Beniston et al., 2000). As such, the quantification of biomass burning activity is now a major focus in the global change community and the large-scale, repetitive measurements required to quantify terrestrial fire activity mean Earth Observation (EO) satellites have been identified as a key technology for the study of pyrogenic activity and the assessment of emissions (Robinson, 1991). However, whilst the emission of certain chemical species and particulates can in theory be examined directly through the use of EO (Kaufman et al., 1990; Goode et al., 2000; Kita et al., 2000; Kaufman et al., 2002), not all species are easily inventoried in this way. Instead the majority of EO-based studies of fire emissions have been limited to mapping the location of active fires or burnt areas (Scholes et al., 1996), with little information provided on the fire physical characteristics such as fire intensity, rate of spread, etc. The absence of this information has been highlighted as a potential problem in certain studies of fire ecology (Whelan, 1995; Morrison, 2002), as has the reliance on maps of burnt area to estimate the amount of biomass combusted in the fire event (Andrea and Merlet, 2001). This is because the relationship between remotely measured
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Spatial Modelling of the Terrestria
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Copyright C○ 2004 John Wiley & So
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Contents List of Contributors Prefa
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Contributors Jonathan L. Bamber Sch
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List of Contributors xi George Perr
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xiv Preface in theory and applicati
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2 Spatial Modelling of the Terrestr
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Editorial: Spatial Modelling in Hyd
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Editorial: Spatial Modelling in Hyd
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2 Modelling Ice Sheet Dynamics with
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Modelling Ice Sheet Dynamics by Sat
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36 Spatial Modelling of the Terrest
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4 Using Coupled Land Surface and Mi
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Coupled Land Surface and Microwave
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100 Spatial Modelling of the Terres
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Editorial: Terrestrial Sediment and
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Editorial: Terrestrial Sediment and
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6 Remotely Sensed Topographic Data
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Remotely Sensed Topographic Data fo
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11 Modelling the Impact of Traffic
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Modelling the Impact of Traffic Emi
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PART IV CURRENT CHALLENGES AND FUTU
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268 Index Bi-spectral InfraRed Dete
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270 Index floodplain maps, UK 92 fl
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272 Index Long-Term Ecological Rese
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274 Index snow depth measurement ne
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276 Index urban land use in remotel
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