How smoky are peat fires?

Deforestation in Equatorial Asia has been increasing in recent decades, as oil palm plantations spread out into the tropical forests of Borneo and Indonesia [1]. And as UBoC PhD student Laura Kiely has found from her research, while loss of habitat from this encroachment is often shown in the media, deforestation can have other, less well known impacts on the air quality and climate.

Fires are used to clear land for plantations, and the land is then drained, so it becomes more susceptible to future fires. [2]

Smoke can cause serious issues to human health, and it has been shown to warm the atmosphere and reduce rainfall [3][4], which could further deteriorate tropical forests (Figure 1) [5].

Understanding the amount of smoke emitted from fires is therefore important for understanding the full impacts of deforestation.

Indonesia differs from other areas of the tropics as it contains large areas of peatland, a type of soil made up of decayed vegetation. This peatland builds up over thousands of years and can be several meters deep. The exact size of Equatorial Asia’s peatland is still unknown. When tropical forest covers this peatland it is kept moist and so difficult to burn. However, where deforestation occurs, the peatland is left vulnerable to fire. [7]

When vegetation on this peatland is burnt, the peatland burns too. Instead of the large, fast moving flames associated with forest fires, peatland fires can burn underground to varying depths, and can smoulder for a long time after the forest fire on the surface has burnt out (Figure 2).

This means they could be emitting more smoke than a vegetation fire covering a similar area. How much smoke, however, isn’t fully understood. Previous studies have highlighted the issues surrounding modelling peatland fires, and these fires are blamed for differences between modelled and observed smoke

The amount of smoke a fire emits can be estimated based on the location, land type and size of the fire; but when it comes to peat fires it can be difficult to determine the size, or to measure how long the fire burnt for. Often the burned area left behind after a fire (detected by satellites) is used to measure the size of the fire, and this doesn’t account for the depth burnt to underground.  In this way, smoke from the peat fires could be misrepresented.

For the first part of her PhD, Laura has been looking at how much smoke comes from these peatland fires, and how well represented they are in current data. This has involved comparing the smoke emitted from fires in peat and non-peat areas, using observational data on smoke in the air as a reference point. So far, it looks as though the current data may be struggling to correctly represent smoke from peat fires.

Next she will be running a climate model, which takes the smoke from these fires and simulates its effect on the atmosphere. Once the smoke from peatland fires is better understood, it can be used in climate models to study the full impact of deforestation on the climate in the region. Laura will then use the model to study the effects of deforestation on rainfall in Borneo.

References

  1. Gaveau, D. L. A. et al. Rapid conversions and avoided deforestation: examining four decades of industrial plantation expansion in Borneo. Rep. 6, 32017 (2016).
  2. Aiken, S. R. Runaway fires, smoke-haze pollution, and unnatural disasters in Indonesia. Rev. 94, 55–79 (2004).
  3. Tosca, M. & Randerson, J. Do biomass burning aerosols intensify drought in equatorial Asia during El Nino? Chem. Phys. Discuss. 9, 23319–23348 (2010).
  4. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp. (2013).
  5. Phillips, O. L. et al. Drought-mortality relationships for tropical forests. New Phytol. 187, 631–646 (2010).
  6. Page, S. & Banks, C. J. Tropical peatlands : Distribution , extent and carbon storage-uncertainties and knowledge gaps. (2007).
  7. Carlson, K. M. et al. Committed carbon emissions, deforestation, and community land conversion from oil palm plantation expansion in West Kalimantan, Indonesia. Natl. Acad. Sci. 109, 7559–7564 (2012).
  8. ‘Indonesia’s Joko Widodo seeks forest fire help’. Online: http://www.bbc.co.uk/news/world-asia-34472085. Accesses on: 20/10/2017 (2015)
  9. Chitra, J. ‘No more forest fires in 2016? Good land use is the key’. Online: http://indonesiaexpat.biz/featured/indonesia-forest-fires-land-management/. Accessed on 20/10/2017 (2015)
  10. Kaiser, J. W. et al. Biomass burning emissions estimated with a global fire assimilation system based on observed fire radiative power. Biogeosciences 9, 527–554 (2012).