Lightning that strikes the ground is of two main types. One effectively transfers negative charge to ground, and the other positive. They may contain a special component, called the continuing current. A positive discharge has a continuing current about 95% of the time, a negative discharge about 20% of the time. The continuing current is the feature of the discharge that starts fires. The discharge leaves distinct traces that, when combined with the characteristics of the fire pattern, can indicate lightning as an ignition culprit.

A nice lightning primer is HERE.

The efficiency of the continuing current as a fire starter depends on the moisture and type of the litter/duff fuels on the ground. In other words, it's the fuel! This efficiency ranges from 4% to about 10% in wildland fuels. Current and past lightning efficiency plots for the US are at the USFS Wildland Fire Assessment System site HERE.

Lightning may be blamed for ignitions it does not cause. Power line ignitions can resemble lightning ignitions, and even electric fences or other sparks/arcs can light fires.





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