What Causes a Forest to Catch Fire?

Imagine a forest like a big campfire. When it gets too hot, or when there's not enough water around, the trees and leaves can catch fire easily, just like how paper burns in the sun. Lightning is one way forests start to burn, but sometimes humans make fires too, like when they leave a campfire unattended.

Once a forest catches fire, it spreads fast because of wind, and if there's no rain for days, the fire can grow bigger and bigger, like a wildfire.