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At a very rough estimate, what proportion of wildfires are caused by natural events like lightning? I am absolutely sure that in Europe, where there are often wildfires, the sun is never hot enough to set fire to vegetation directly, though it obviously makes things tinder dry and easily combustible. The broken bottle theory has been disproved. Experiments involving broken glass among highly combustible straw or hay were unsuccessful in causing combustion, though manual focussing of the suns rays with the lens-shaped bottom of a bottle were on rare occasions and with much difficulty successful. Although lightning undoubtedly causes the occasional wildfire, the majority have no connection with lightning. It should also be remembered that lightning is usually accompanied by torrential rain. These fires often start in several places at once, which is stretching the long arm of coincidence a bit too far.

Apart from the very rare instances of volcanos causing wildfires, what other natural causes could there be? Comparison of wildfire frequency in tinder-dry uninhabited areas, well away from civilisation, versus frequency in or near similar but populated areas should give a good idea of the scale of the problem.

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    $\begingroup$ Only the first sentence is the actual question. The following wall of text are various claims, opinions, and thoughts with differing relatedness to the question. Can you please focus and edit your question so it is answerable? $\endgroup$ – Gimelist Aug 6 at 1:06
  • $\begingroup$ At Spain 95% of wildfires have an antropogenic origin, 50% are deliberated spain gov source. I don't know from where they take those data as the sources are not allways known by autorities. $\endgroup$ – user12525 Aug 6 at 18:46
  • $\begingroup$ This is what I suspected. It's disgraceful that people could do such things. I won't go into a list of all the environmental damage done by wildfires, but the list is long. Perhaps worse, people are often killed by these needless fires, just to entertain a few nut cases. $\endgroup$ – Michael Walsby Aug 6 at 19:04
  • $\begingroup$ Maybe at other countries there are more than 5% of natural wildfires, as at Spain they used to burn the forest to speculate with soil. The law is trying to stop it I think with measures as not to permit to construct in burned zones, but deliberated fires still occur. Sometimes they are menthal illness people (they could immolate theirselves if they are trying to claim something). In what concerns not deliberated but human, tobacco is the main source (barbecues with no care the second). Philipp Morris was obligated to eliminate the fuel the cigarrette papers have, at least at my country. $\endgroup$ – user12525 Aug 6 at 19:32
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    $\begingroup$ "... lightning is usually accompanied by torrential rain..." In the arid western USA, where I was a wildland fire fighter for eight summers, lightning storms are commonly accompanied by very little rain (the regional colloqiualism is "dry lightning"). Even with torrential rain, a lightning-struck tree may smolder internally for a long time only to reignite as conditions dry out. As a fire lookout, I would remain especially vigilant for up to two weeks following a "wet" lightning episode. $\endgroup$ – Stu Smith Aug 7 at 15:04
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There was an interesting paper on this for the United States a couple of years ago:

Balch et al (2017) Human-started wildfires expand the fire niche across the United States, PNAS, doi: 10.1073/pnas.1617394114

They estimate that in the coterminous U.S. human-started events account "for 84% of all wildfires and 44% of total area burned". There is a marked spatial variation, with lightning-started wildfires occurring mainly in the more sparsely populated western forests. If you have access, the paper's worth a read, it has lots of interesting figures picking apart the details.

enter image description here

It's worth noting that there are a number of reasons for human-started wildfires, which are could be classed as accidental, deliberate or careless:

Human-started wildfires were caused by a variety of sources, including the US Forest Service-designated categories of equipment use, smoking, campfire, railroad, arson, debris burning, children, fireworks, power line, structure, and miscellaneous fires.

They also note that their data contains this, perhaps not unsurprising, feature:

There was also a notable mark of American culture on the distribution of wildfires, with the peak day of wildfires occurring on July 4th, concurrent with Independence Day fireworks displays (Fig. 2). Indeed, Americans start over twice as many wildfires on July 4th as any other summer day.

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  • $\begingroup$ We need to find some way of dealing with it. There's nothing we can do about lightning, but we need to find and punish the pyromaniacs responsible. I bet Hitler would soon have had the problem under control if it had happened in Germany. Not everything he did was bad. A pyromaniac burned down the Reischstag in 1933,and he had his head chopped off! Do gooders, bleeding hearts and pioneers of political correctness got frogmarched to a concentration camp. $\endgroup$ – Michael Walsby Aug 8 at 17:04
  • $\begingroup$ @MichaelWalsby Even as a Brit, I think that capital punishment for celebrating Independence Day is a bit much. $\endgroup$ – Deditos Aug 9 at 9:34
  • $\begingroup$ I agree, but I'm just telling you what Hitler would have done with pyromaniacs who started fires deliberately. Those guilty of starting them through carelessness would have got more lenient treatment, but would not have gone unpunished if the fire was a serious one, and especially those fires which caused loss of life. $\endgroup$ – Michael Walsby Aug 9 at 9:44

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