by Mountaineerbr

#9 - What causes forest fires?

Em anos anteriores o lema na imprensa era Amazônia em Chamas!. Este ano estamos vendo Pantanal em Chamas!.. Há a formação de uma La Niña fraca no oceano Pacífico, e a região ~sudoeste do Brasil ficou mais seca, enquanto que a região ~nordeste (provavelmente cerrado) e também a Amazônia ficaram mais úmidas.

Decidi fazer uma lista genérica com possíveis causas naturais de incêndios florestais pois a imprensa parece saber somente de uma (incêndios criminosos), mas há uma literatura enquanto que enterrada pelo tempo, rica em informações relevantes, e muitas vezes, revelantes.

There started again the annual talk of forest fires! In the last two years, the headlines were Amazon is on fire! and now they are Pantanal is on fire!. For those who are not familiar with what a Pantanal is, it is actually a Brazilian ecosystem, which terrais flood in the rain season and dry up in the dry season, so there are many bogs and meandering rivers.

We are currently in the dry season! Also, this year it seems we are having a weak La Niña, which makes the Pantanal region (and where I live, some further south at the Capricorn Tropical Line), drier. On the other hand, the Amazon, cerrado and thereabouts in the northeast region, are in their turn more humid, and of course there are less forest fires there than the previous years.

I have been reading some material about fire management and found some very good Brazilian and Portuguese papers and documents. Specially, Portugal has got competent technical knowledge on the subject. In one the of the papers, after explaining Portugal fire index system through history (from ~1960), the author acknowledges the index could be far more useful for society if forest and fire management could make use of it!

I decided to start compiling a list of causes of forest fires other than criminal human or indigenous activity, which seems to be the only cause of forest fires the media knows and talks about.

This is a general list, forests may be more prone to some causes than others depending on geography and other factors. That is a shame I did not start making this list a few days ago, now it is rather hard to find some of the references and I can't be 100% sure about some technical wording, so while not ideal, I will link to similar references, leave them without reference or remove the item from the list eventually.

Causes of forest fires:

More links

Interesting quotes

Deve-se distinguir claramente a diferença entre uso da terra e desmatamento. Todo desmatamento é uma forma de uso da terra, mas nem todo uso da terra é um desmatamento. Deve-se portanto, quantificar separadamente uso da terra e desmatamento. As áreas agrícolas (uso da terra) fora da região do domínìo da floresta tropical úmida que ocorre nas regiões de savana (cerrado, campos cerrados) dos estados periféricos da Amazônia Legal (Mato Grosso, Tocantins, Pará, Maranhão) não devem ser consideradas como áreas desmatadas e não o foram neste relatório. [..]
CONTRARY to widespread belief, evidence is mounting that pre-Columbian America was not a pristine wilderness inhabited by people who lived in such harmony with nature that they left it unmarked. Instead, many scientists now say, the original Americans powerfully transformed their landscape in ways both destructive and benign -- just like modern people.
[...] more extensive fires on the alluvial islands of the middle Rio Negro were those of the1925/26 El Niño year, witnessed and poetically described by Marchesi (1975): Thunder and lightning appeared every day without rain. Then the great forest fires began. Flames crossed from one side of the river to the other... Dense smoke covered the entire region, eclipsing thesolar disk. It was night for us too on the upper Rio Negro where the fire had not yet arrived. Weasked ourselves if it weren’t the end of the world. Finally, in early April after 100 days of drought unlike any known before, a tempest struck.

Fire triangle

fire triangle schematics
Fig 1. This triangle is used throughout many booklets about fire, and it draws attention the fact that is composed of only three (essential) parts: oxidizer, heat and fuel. (credit: University of South Carolina)