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Polluting fires the result of human activity
The enormous forest fires that rage throughout Indonesia during periods of low rainfall cannot be attributed solely to severe drought. A team of researchers, including Veni winner Guido van der Werf, analysed the density of smog generated by these forest fires. They have firmly established that population density and land use have a significant influence on the ferocity of forest fires. Nature Geoscience published the results of this study on 22 February.
The greatest problem posed by Indonesian forest fires is not the fire itself, but the noxious smoke created by such blazes. In Indonesia, the death toll from this smoke is probably many times greater than that in Australia this year. The smog also causes enormous environmental damage. It is essential to find out as much as possible about the causes of these blazes in order to improve our ability to forecast major forest fires.
There is no smoke without ...
The researchers analysed Indonesian forest fires using the dense smoke released from these infernos. In the absence of good satellite imagery, little is known about the fires that occurred prior to the 1990s. The researchers circumvented this problem by using daily records that have been kept for the last fifty years, coupled with visibility observations and meteorological data from various airfields.
One of the most striking results of the study is that low rainfall in Sumatra has caused fires since as long ago as 1960, while this has only been the case in Kalimantan since 1980. Prior to 1980, Kalimantan came through these dry periods very well, but in the years since then this province has become extremely sensitive to fires in periods of drought. The population of Sumatra grew substantially during the 1960s. A comparable level of population growth did not develop in Kalimantan until the 1980s.
In addition, this increase in population in Kalimantan was accompanied by a shift from small-scale agriculture to large-scale industrial agriculture. This transformation involved the drainage of large areas of peat bog and large-scale deforestation. It was these changes in population and land use that caused Kalimantan to become more susceptible to fires. It has long been suspected that these large-scale effects resulted from human activity. However, this is the first study to obtain the reliable data needed to demonstrate that this is indeed the case.
Climate change
In addition to those major effects that are largely the result of human activities, the researchers investigated the influence of two climatological phenomena. El Niño has long been known to affect levels of precipitation, but the Indian Ocean dipole (a phenomenon that has great influence on ocean surface temperatures) has been shown to be an equally important factor.
While severe droughts create the conditions for forest fires, it is often people who actually initiate these conflagrations. Many of these fires are deliberately set, in order to clear land for cultivation. In addition to the greenhouse gases carbon dioxide and methane, the combustion of biomass over an extended period also releases large amounts of carbon monoxide and particulate matter. As a result, during those years in which there are major fires, air quality in Indonesia is many times worse than in the world’s most highly polluted cities. This polluted air also causes problems in areas far removed from the fire zones.
Guido van der Werf, a researcher at VU University Amsterdam, carried out this study in collaboration with Robert Field and Samuel Shen. In 2008, Dr van der Werf won the Netherlands Organisation for Scientific Research’s Vening Meinesz prize for the most promising recent PhD graduate in the earth sciences.
The article entitled ‘Human amplification of drought-induced biomass burning in Indonesia since 1960’ was published as an Advance Online Publication on the Nature Geoscience web site, at 19:00 on 22 February.
Human amplification of drought-induced biomass burning in Indonesia since 1960 (pdf)
