How much water vapor do forest fires contribute to the atmosphere?

Dear Tom,
How much water vapor do forest fires contribute to the atmosphere? On a trip to Arizona last year I saw a cloud develop over a forest fire. Smoke from the fire rose and gave way to a white billowing cloud above the smoke.
Sam Hurley, Rockford
Dear Sam,
It’s not that the forest fire generated or added moisture to the atmosphere. Instead, the heat of the fire caused air over the fire to rise high enough that the air chilled to its condensation temperature and produced clouds. Those clouds even have a name: Pyrocumulus. Pyroculumus clouds owe their development to the heat of fires beneath them and to preexisting moisture in the air. They dissipate as they move away from the fires. Pyrocumulus formation similarly occurs over smokestacks venting exhaust from industrial processes.

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