Bolts from the blue: lightning and forest fires

Lightning arcing through a conifer tree in Arizona, USA (photo sent to me by Phil Cheney)

Like most people, lightning both scares and fascinates me.

It is not just the colossal, explosive power and the thunderous sound effects, but the fact that a lightning strike is somehow so arbitrary and undiscriminating. It can strike anything or anyone. Lightning can even strike down from a clear sky, having originated from a thunderstorm twenty kilometers away. [This phenomenon, incidentally, is the origin of the expression “a bolt from the blue”, a phrase that has come these days to describe (appropriately) any totally unexpected and usually unhappy event].

But apart from the fear and awe conjured up by a noisy and flickering thunderstorm, lightning has also played a significant part in my professional life. This has been through its agency as an igniter of bushfires. Over the years, I have had to confront the consequences of lightning-caused fires in various ways and across a wide spectrum: from digging firebreaks with a shovel (when I was a firefighter in a forestry gang in 1961), to designing fire management strategies for forests prone to summer thunderstorms (when in the 1990s I was a senior land management officer). Lightning, and lightning-caused bushfires are a fact of life in the south-west forests of Western Australia, where I spent all those years, and nobody likes them. They cannot be prevented and their precise location cannot be predicted, and all too often the consequences can be, and usually are, extremely unpleasant.

Luckily, I have never been struck by lightning, unlike my former sister-in-law who took a jolt from a lightning strike in the Yemen many years ago. I think she only survived because my brother, a doctor, was present at the time and took the necessary ressusitative action on the spot.

You would think the fact that lightning bolts start forest fires would not be controversial.

I have always thought it self-evident. A highly concentrated shaft of enormous electrical energy strikes into dry grass, leaves or shrubs, or into the crown of a tree with volatile foliage. This raises the temperature of the earth connection above ignition point, and bingo, you have fire. Then if conditions are suitable, you can also get a bushfire.

It is also self-evident that fires caused by electricity are omni-present and can hardly be described as imaginary. Every summer firefighters have to deal with bushfires caused by faulty or fallen powerlines – this is one of the most common causes of bushfires right across Australia these days. Moreover, electrical fires are caused by the sparkplugs within the internal combustion engine that powers my motorcar. And increasingly these days we read about the spontaneous combustion of electric vehicles. I would not have thought you would need a degree in physics to understand the principle or the process: electricity can start fires, and lightning is concentrated electricity.

But to my consternation one day I found that there is a bevy of environmentalists who actually deny all this. “Lightning does not cause bushfires,” said one of their most aggressive spokeswomen at a public meeting I once attended. “These so-called lightning fires are secretly lit by foresters who are looking for paid overtime for the firefighting, and who blame the fires on lightning”.

To say that I greeted this statement with incredulity (verging on anger) would be an understatement, especially as I had been a firefighter during the 1961 bushfires in Western Australia when lightning-caused fires burned down whole towns, including the homes of many foresters, and no overtime at all was paid to the foresters striving to put them out.

In January 1961, there were 19 separate fires started in jarrah forests near Dwellingup in a period of about 24 hours, from two massive lighting storms. In the summer of 1960/61 the entire southwest was swept by repeated lightning storms, and many strikes resulted in catastrophic fires.

The question of whether lightning causes forest fires was also a matter of contention in 19th century India, as I discovered one day when leafing through back issues of my favourite journal, The Indian Forester. In the 1885 edition I came across this letter to the editor from a forester working in Jaunsar:

In the Annual Report… for the North-West provinces for 1883-4, you will observe that the Conservator makes special mention of a forest fire having been caused ... by a flash of lightning. [The Conservator] … seems to be somewhat doubtful of the credulity of the report.

It may, however, interest some of your readers to learn that an exactly similar case occurred in June 1882, and which came to my immediate notice. In this case a kail (Pinus excelsa) tree was struck by lightning, and the electric fluid, having split the tree, at once set fire to the grass at its foot, and about an acre was burnt before the conflagration was extinguished by the Forest Guard and some villagers who happened to be near.

I visited the place a few weeks afterwards and satisfied myself that the fire was due to lightning, and to no other cause.

There was a follow-up to this story. According to this correspondent:

On the 30th April about 5 pm a thunderstorm passed along the Siwalik Hills, and in its course a flash of lightning struck a young green sal tree of some 18 inches girth on one of the numerous summits of the range about two miles north of the Beribara Rest House.

This tree was at once in a blaze, and one of its branches falling onto the grass beneath, at this time of the year as dry as tinder, set it on fire, which was at once carried by the wind into the surrounding jungle. In spite of the storm of rain, the fire burnt over some 300 acres before it was finally extinguished.

There are about 12 feet of the trunk of the tree still standing, all charred and burnt ...

And finally, under the heading ‘An Authentic Case of a Forest Fire Caused by Lightning’:

... readers of The Indian Forester will be interested to learn of an authentic case of a forest fire caused by lightning, which occurred last April in the Alapelli forests of the Chanda District of the Central Provinces. During a heavy thunderstorm a large teak tree was struck in the Mirkalu reserve which, it is hardly necessary to say, is protected from fire.

The lightning current first struck an upright branch and then ran down the stem setting it on fire. The tree was shivered to pieces, large fragments being scattered over long distances. The storm being accompanied with but little rain, the grass and dry leaves round the burning tree were set ablaze. As this unfortunately occurred in the middle of the night, more than 80 acres were burnt before my establishment could reach the spot and extinguish the fire.

I enjoyed these little stories from India, firstly intrigued by the need for the writers to support the “controversial” notion that lightning causes forest fires, but also because they confirmed my own experiences and those of many of my colleagues. I read a good example of this recently, in a memoir sent to me by fire ecologist Neil Burrows. He recalled his involvement in the investigation of a serious fire at Kin Kin in 2013:

This fire was one of eight lightning-caused fires associated with thunderstorm activity on 12 and 13 February 2013. Seven of the fires were suppressed by departmental firefighters when less than one hectare in area.

I was called in to investigate the Kin Kin fire, the one that got away. It was started by a lightning strike in State forest about 25 km sout-east of Manjimup on 13 Feb 2013. The fire burnt about 1200 ha, most of it in old fuels (10-30 yo). It was eventually controlled when the headfire ran into 4-year-old fuels. I was able to backtrack to the source of the fire, and found the lightning-struck marri tree where it all began. The photo below shows the classic lightning-caused spiral ‘gouge’ down its bole.

Bushfire specialist Lachy MCaw also told me an interesting story about a lightning-caused fire:

It was an early season (late October) lightning strike that ignited dead wood in the topmost branches of a tall, dead karri tree. A logging crew on their way to work early in the morning saw smoke, found the burning tree and reported it. Because the tree was tall and well alight it had to be felled and this was done by the Parks crew from Pemberton when they arrived on site. Had this burning tree not been detected and reported it could have burnt down slowly from the top for several weeks as the spring weather warmed and the ground fuels dried. Eventually the bush might well have been ignited. Lightning fires in October are uncommon in the karri forest but not unknown. They indicate that spring fires do occur.

Not every lightning strike starts a bushfire, in fact most do not, especially those during the winter months when the bush is saturated. I recall a time in the 1970s when I drove out along the Graphite Road west of Manjimup on the morning after a heavy overnight thunderstorm. Just before the steep pinch where the road drops down into the valley of the Donnelly River I came across a large marri (Eucalyptus calophylla) tree on the road verge that had been blown to bits by a lightning bolt a few hours previously. For a radius of thirty metres in all directions neighbouring trees had been peppered with tiny match-sized spears, and thousands of these were deeply embedded in their trunks. Anybody standing near the marri when it was struck, had they survived at all, would have suffered terrible shrapnel wounds.

A mature jarrah near Nannuup, shattered by a lightning strike. This occurred during winter, and no fire resulted, but the power of the strike was such as to throw chunks of timber up to 100 metres from the strike (details and photo by Kevin Coate)

The power and intense heat of a lightning bolt was also witnessed by forester Jack Bradshaw:

I was out in the Big Brook karri regrowth forest one day and I came across a tree that had been struck by lightning. It had been killed stone dead. What I found interesting was that there was a circle of trees surrounding it, in which only the ‘inside’ edges of the trees (those facing the tree that had been struck) were damaged. The bark and foliage that had been exposed to the lightning were dead, but the trees were still alive. I had never seen such a thing before or since.

Thinking about these blasted trees, I reflected briefly on the fact that I had once worked for a while as lookoutman on the Gardner Tree, fire-watching from a cabin bolted into the uppermost forks of the tree, two hundred feet above the ground. What would have been the consequences of a lightning strike on the Gardner Tree while I was in the cabin? It was a sobering thought. All of the tree lookouts in the karri forest were equipped with lightning conductors (a heavy copper wire running from the roof of the cabin to the earth below), but their efficacy was never tested (or at least never reported). I suspect that I would have been blown to bits.

I also recalled the time I was the district forester at Pemberton and a massive dry thunderstorm rolled down on us from the north. Standing on the office veranda I could hear and see it approaching across the farmland at Eastbrook and north-Pemberton. It was a fearsome experience. We ended up that day having to deal with numerous fires on farms and in the bush, but fortunately nothing too difficult; on that occasion, as sometimes happens, the lightning had been accompanied by thundery showers, making them easy to control. However, showers accompanying lightning are not always a bonus. Every firefighter is alert to the likelihood of “sleepers” after a lightning storm. These are fires started by a bolt, then dampened down by light rain, but not extinguished. Later when the weather warms up, the sleepers awake, and a rash of new fires start.

And yet, while I have no doubt that lightning strikes can start bushfires, I never actually saw it happen. Never, that is, until one day in December 2005 when I was working in the Kimberley region in the north of Western Australia. The Kimberley has a sub-tropical climate with a long, lovely dry season from about March to October, followed by a transitional and unsettled season known locally as ‘the build-up’ through November and December. Then, usually just after Christmas, the monsoon arrives, heralding a hot, humid rainy season (known locally as ‘the wet’) that lasts for about the next three to four months. I recall:

Late in the afternoon of a trying, hot and humid day, typical of the build-up, I was on my way home after a long day in the field, driving back to Kununurra where my motel promised an air-conditioned bar. My colleague Chris Done and I could see a towering black thunderstorm up ahead. The late afternoon sun was glowing on the roiling cloudtop reaching thousands of feet into the sky, and the whole animal was shot through with flickering lightning.

Not far from town I actually saw a lightning bolt strike into the bushland on the ranges north of the road on which we were driving, about five kilometres away. It was accompanied by an almost instantaneous and almighty metallic thunderclap. Within seconds, we could see smoke rising from the strike point, and then flames. Within minutes the fire was going well and covered about half a hectare; the flames appeared to be about three to five metres high. “This is going to be interesting,” I thought.

It was, but not for the reason I expected. We had slowed to watch and in less than about 10 minutes from fire ignition, the heavens opened and a massive deluge of rain thumped down. Having watched nature at work starting the fire, I watched it finish the job by putting it out. In another minute or two our vehicle was also engulfed by the deluge, the water cascading down as if we had parked under a great waterfall. Driving was impossible as we could scarcely see over the bonnet of the Land Cruiser.

Within fifteen minutes it was over as quickly as it had begun. The sun came out and everything was steaming. The fire in the ranges was no more than a memory.

Ordering a beer in the bar that night, my lips suddenly pursed, remembering that environmentalist who categorically denied that lightning starts bushfires. I almost wished she had been there with me that afternoon to see it with her own eyes. But the more I visualised this, the less the vision appealed to me, especially compared with that of the foaming pint glass before me. I turned to the beer with relief.

I don’t think I have ever read an article in an Australian forestry or bushfire journal from firefighters seeking to authenticate the fact that lightning causes bushfires. It seems to me that this has always been taken as a given, based not only on their own experiences, but on those of the Aboriginal people and the generations of bushmen and pioneer settlers who knew and worked in the bush before foresters arrived on the scene. Furthermore, we now have heat-seeking satelites that can observe and map lightning strikes, and the relationship from strike to bushfire is completely transparent. Apart from anything else, these images provide a graphic demonstration of the poultice of strikes that can reach earth from one thunderstorm.

Satelite mapping of the strikes from a single thunderstorm that traversed the south-west of WA in January 2023 (image courtesy of Ed Hatherley)

One of the other advantages modern bushfire managers enjoy is that lightning storms have become easier to forecast … the storm, that is, not the location of a strike. Meteorologists have instruments that can measure the electrical charge in the atmosphere, and they can calculate the risk of a lightning storm developing. It is no longer necessary to stand on the office veranda, listening to the thunder, and watching the storm approach.

I was thinking about this recently when re-reading Green Mountains by Bernard O’Reilly, a classic in Australian pioneering literature. O’Reilly was one of the first settlers to carve farms from the great rainforests that later became surrounded by the world-renowned Lamington National Park in southern Queensland.

Like most intelligent pioneering settlers, Bernard O’Reilly had a profound interest in the weather. I loved his observations on thunderstorms and lightning. These display the understanding of the natural world around them that bushmen needed before the days of weather forecasts, satelites and other modern technology:

Perched as we are on the roof of Queensland we have a unique opportunity of studying the weather … when a storm is still a long way off it is frequently possible to forecast what kind it will be ...

… storms with dangerous lightning are unobtrusive-looking in the distance, their formation is high, the clouds smooth, even-coloured greyish black with sometimes a touch of brown, but it is the sound of their thunder which gives warning. Even at a great distance it is possible to identify a type of lightning by the sound of the thunder; it must be obvious that chain lightning which takes the shortest cut from a negative cloud to the positive earth, must make a sound entirely different from that of the harmless brush lightning which writhes across miles of sky and branches out into a hundred leads. More than once when on the point of starting home from the Stockyard Creek depot with packhorses I have been warned by a distant barrage of separate metallic explosions unaccompanied by any rumble; I would unpack and stay under the little iron roof while big trees were blown to splinters up along the stony ridges where the homeward track lay ...

An unpopular feature of many lightning strikes/fires is that they occur in remote and dense forests far from a road. I can remember during the 1961 fires that our crew had great difficulty in finding the fire we had been sent to extinguish, and then having to walk in through thick karri bush, carrying our equipment. Things are better these days since the advent of spotter aircraft - they can give a precise GPS of a fire and communicate this to firefighters. And while I am opposed to the deployment of huge water/retardant bombers, there is a key role for the small, agile water bomber which can be rapidly on the scene of a lightning strike and (provided conditions are not extreme), hold a fire in a remote spot until ground crews arrive.

A lightning strike in remote forest (photo ex-Google)

I don’t do much firefighting anymore, and I try to stay out of the way when lightning is around. However, the threat of a strike and of a resulting bushfire is always at the back of my mind. This is especially so when I am up on our property at Gwambygine in mid-summer and the whole countryside is tinder-dry. I keep the paddocks mown, and the fuels down under my trees, just in case, and I have an old forestry fire rake which still works (even if the man behind the rake is not as tough and supple as once was the case). But I don’t like summer thunderstorms, or the prospect of a large fire sweeping in on us.

Moreover, I always stand-to when the occasion demands. Only last summer, on a day of extreme heat and blustery wind, a fierce electrical storm came at us over the ranges, complete with jagged lightning bolts and almighty claps of thunder. I put on the boots, overalls and hard hat, filled buckets and gutters, had the rake, hose, shovel and mop handy, and waited, ready to defend my cottage and my woman, or go down with them.

But the drama passed. The storm rolled and rumbled off to the west and we were unscathed. I was almost disappointed. It would have provided a grand finale to a life in which the risk of bolts from the blue and nasty bushfires, like Damocles Sword, was always hanging just over me.