> But a lawn fire is not directly temperature related, is it? The rate of evaporation is directly related to the temperature. Even ignoring additional factor

> But a lawn fire is not directly temperature related, is it? The rate of evaporation is directly related to the temperature. Even ignoring additional factors affecting evaporation like wind and topographic variance in dryness, the vapor pressure of water (the biggest contributor to evaporation rate) at 40C is an order of magnitude higher than it is at 20C: https://en.wikipedia.org/wiki/Evaporation#/media/File:Water_vapor_pressure_graph.svg https://en.wikipedia.org/wiki/Evaporation#/media/File:Water_... Sufficient subsequent days of high heat and low humidity will dry out a lawn very quickly, as grass is a plant that is not adapted to retain moisture very well. With hot/dry enough conditions for a sufficient period of time and a bit of kinetic energy in the form of wind, grass that isn't watered quickly becomes flammable, which is why it is usually where large fires first take hold.