On Aug. 18, lightning struck a heavily wooded area near the Ontario-Manitoba border, sparking a blaze dangerously close to some cottages on Lake of the Woods.

The moment it happened, the bolt's location showed up as a bright mark on a computerized map, warning fire officials at the Ontario Ministry of Natural Resources that conditions were ripe to nurture and grow a dangerous inferno.

Lightning detected near Lake of the Woods in northwestern Ontario on Aug. 18 prompted aerial patrols that found a fire dangerously close to some remote cottages.Lightning detected near Lake of the Woods in northwestern Ontario on Aug. 18 prompted aerial patrols that found a fire dangerously close to some remote cottages. Ontario Ministry of Natural Resources

“They knew that that was a critical area — they’d had only a little bit of rain on very dry forest fuels,” said Mick Rice, weather systems co-ordinator for the ministry’s aviation, forest fire and emergency services.

Over the next couple of days, aerial patrols were sent out to within 20 kilometres of the lightning strike and, sure enough, they spotted a telltale column of white smoke spiraling up from the trees. It was a small blaze, just 0.1 hectares in size, but too close to the cottages for comfort.

By the time the fire had grown to 0.4 hectares, crews were on the scene and quickly extinguished it, keeping the cottages safe.

If lightning comes with rain, how does it start fires?

Mick Rice of Ontario's Ministry of Natural Resources says there are a number of “dry lightning” scenarios that can spark a blaze.

One that occurs rarely in Ontario, but more often in drier areas such as the Northwest Territories, involves lightning from big thunderclouds high above the ground during hot weather. Under those circumstances, the rain unleashed by the clouds may evaporate before it hits the ground.

In Ontario, dry lightning most often occurs when a lightning bolt lashes out of the side of a cloud, landing away from the rainstorm itself. Fire will be "almost instantaneous," Rice said.

However, more often the cause of these fires is that lightning, accompanied by rain, strikes well into the undergrowth, causing it to smoulder deeper than the rain can penetrate. When the surface layers dry off after a few days, the smouldering fire can work its way to the surface. That can take up to a week after the lightning strike itself.

2011 a bad year

Lightning starts about a third of all fires in the province, and this has been a particularly bad year for lightning-caused fires compared to those caused by humans, Rice said.

As of Aug. 29, 1,000 fires had burned 628,859 hectares of Ontario forest — greater than the area of Prince Edward Island and nearly 10 times the average of 68,108, for this time of year, over the past 10 years.

And even though the fire season tends to wind down in the fall, it's not yet over. In fact, Environment Canada is predicting a warmer-than-average fall across much of the country and drier-than-average conditions in some areas.

In areas where there are homes and communities, fire crews are deployed quickly to stamp out fires when they are small, to minimize their damage and the destruction of property and infrastructure such as power lines.

Unlike Alberta, which has forestry towers to keep an eye out for wildfires, Ontario relies on aerial patrols to cover its vast expanses of boreal forest.

Knowing where fires are likely to have started makes it possible to send patrols to the right place at the right time. That’s where the province’s 30-year-old lightning detection network plays a key role.

Fifteen detectors, which are regularly upgraded and replaced, are spread across the province, mainly toward the southern end of the northern boreal forest, where more humans live.

When lightning strikes, it generates a radio-frequency electromagnetic radiation that is detected by multiple sensors as far as 1,000 kilometres away.

When lightning strikes, it generates radio-frequency electromagnetic radiation that is detected by multiple sensors as far as 1,000 kilometres away.When lightning strikes, it generates radio-frequency electromagnetic radiation that is detected by multiple sensors as far as 1,000 kilometres away. Ontario Ministry of Natural ResourcesThe sensors have magnets that can tell which direction the pulse came from and they are networked so that a computer can compare the time each one detected the strike.

Closer sensors will detect the signal slightly earlier than one that is further away. Using this information, the lightning can be pinpointed within 100 metres in much of Ontario’s boreal forest.

This past July, the peak month for lightning, the network detected over 177,000 lightning strikes, significantly above the average of 130,000 for that month.

The information is fed into a computer model, frequently tweaked and improved, that overlays the lightning strikes with data about conditions that could increase the likelihood of a forest fire. That tells fire crews where to send the aerial patrols.

Cross-Canada network

Environment Canada launched a network of 80 lightning detectors across the country in 1998. It follows the treeline and is integrated with a U.S. network that includes detectors near the border, said Environment Canada meterologist Terri Lang.

The network is independent of provincial networks such as Ontario’s, and provides information to utilities, airports, weather services and provinces that don’t have their own networks, such as B.C. and Saskatchewan. The users may use them to point to potential forest fires, as well as a range of other uses such as forecasting severe weather warnings, Lang said.

However, for all the system’s sophistication, the information it provides isn't enough to keep all communities safe from the natural fires that ravage the boreal forest each summer.

In July, for example, 3,500 people were forced to flee First Nation communities in northwestern Ontario as smoke and flames threatened to engulf them.

Rice said a main reason the fires were so bad this year in that region was because some had initially broken out further north, and had been allowed to burn.

“We had a lot of lightning east of the Manitoba elbow, where there weren’t too many communites, so we sort of let them go for a bit, and it stayed dry and it stayed dry and they started getting bigger and they started spreading,” he said.

Eventually, the wildfires began roaring dangerously close to human settlements, forcing fire crews to face the growing flames on the fronts nearest the communities.

“By the time they’re actually tackling them," Rice said, "they have some major fires on their hands.”

When deciding when and how hard to fight a forest fire, he added, officials consider both the threat against communties and the fact that lightning-caused fires have been part of nature since long before humans existed. In fact, they play a key role in forest ecosystems and some plants rely on fires to propagate.

“It’s always a balancing act,” Rice said. “If you put every single fire out that erupts, then you’re not really doing nature a favour.”

Ontario's network of 15 lightning detectors are mainly concentrated in the southern part of the northern boreal forest. Ontario's network of 15 lightning detectors are mainly concentrated in the southern part of the northern boreal forest. Ontario Ministry of Natural Resources