What does relative humidity measure?

Relative humidity measures the amount of moisture in the air in relation to the maximum amount of moisture the air can hold at a given temperature. It is expressed as a percentage, where 100% relative humidity indicates that the air is fully saturated with moisture, and any percentage lower than that indicates the air can hold additional moisture. Understanding relative humidity is crucial in wildland fire behavior, as it significantly impacts fire ignition, spread, and the effectiveness of fire suppression efforts. Higher relative humidity can lead to more moisture in vegetation, potentially reducing fire intensity, while lower relative humidity can lead to drier fuels and increased fire behavior.