Lightning-Struck Trees: When Do They Catch Fire in the Rain?

Have you ever wondered what happens when a tree is struck by lightning during a rainstorm? Does the moisture from the rain prevent the tree from catching fire, or does the intense heat generated by the lightning still cause ignition? In this article, we'll explore the factors that influence whether a lightning-struck tree will catch fire in the rain and provide insights from a forestry patrolman’s firsthand experience.

The Myths and Realities

Contrary to popular belief, a tree struck by lightning in the rain can still catch fire, though the likelihood is reduced due to the moisture. A forestry patrolman from decades ago recalls an incident where lightning struck a 30-foot Jeffrey pine, peeling a spiral strip of bark from the top but leaving no fire. The tree eventually died but was never consumed by a fire. This example illustrates that while lightning can generate extreme heat, moisture can sometimes prevent the tree from catching fire immediately.

The Science Behind Tree Ignition

Lightning strikes pack an enormous amount of energy, generating temperatures that can exceed 30,000 degrees Fahrenheit (16,000 degrees Celsius). This intense heat can vaporize water within the tree and ignite it. However, heavy rain can dampen the tree, reducing the likelihood of immediate ignition. Despite this moisture, the residual heat from the lightning strike can cause the tree to smolder or burn internally, leading to a delayed fire once the rain subsides.

Practical Examples

Living in southern Arizona, where monsoon storms are common, several residents have observed trees burning after lightning strikes during rainfall. These fires often occur due to the combination of dry tree material and insufficient rain to extinguish the immediate flames. One local notes, 'I see it every year,' highlighting the frequent occurrence of such events.

Scientific Observations and Studies

Decades ago, a nighttime storm in Inwood Hill Park in northern Manhattan left a massive plane tree with a striking appearance. The lightning struck with such force that the sap was turned into steam and the bark was blown off in large pieces. Despite the intense heat, there was no visible charring. This observation underscores the unusual nature of lightning strikes and their impact on trees.

Conclusion

While it is rare for a lightning-struck tree to catch fire during a rainstorm, the potential still exists. The moisture content of the rain plays a critical role in this process. If the rain is not heavy enough or if the tree has a significant amount of dry material, the risk of a fire increases. Understanding these factors can help in preventative measures and early detection of such incidents.