How does relative humidity change with temperature fluctuations?

Relative humidity is the measure of the amount of moisture in the air relative to its capacity to hold moisture at a given temperature. As temperature increases, the air's capacity to hold moisture also increases, which typically leads to a decrease in relative humidity if the actual amount of moisture in the air remains constant. Conversely, when the temperature decreases, the capacity of the air to hold moisture diminishes, leading to an increase in relative humidity if the moisture content stays the same.

The statement that relative humidity doubles with each 20-degree decrease in temperature reflects this principle accurately, as cooler air holds less moisture, which means that for a constant amount of moisture, the relative humidity must increase significantly. This relationship is crucial for understanding fire behavior as humidity levels can greatly influence fuel moisture and fire behavior patterns.

In contrast, relative humidity does not remain constant with temperature changes, and it does not follow a pattern of 'doubling with each 20-degree increase' either. These options would suggest a misunderstanding of how temperature and humidity interact. Rather, the nature of humidity's response to temperature changes is consistent with atmospheric physics, demonstrating a clear relationship between decreasing temperature and an increase in relative humidity.