Relative humidity increases when which of the following occurs?

Relative humidity is defined as the amount of water vapor present in the air, expressed as a percentage of the maximum amount of water vapor the air can hold at a given temperature. When precipitation falls through an air mass, it adds moisture to the air. This increase in moisture content raises the relative humidity, as the air now holds more water vapor relative to its capacity.

The correct answer illustrates a direct relationship between the introduction of moisture (through precipitation) and the relative humidity levels in the air. When rain or other forms of precipitation occur, it saturates the air, pushing the relative humidity higher.

In contrast, the other scenarios would typically lead to a decrease or stabilization of relative humidity. An increase in temperature generally increases the capacity of air to hold water vapor without necessarily increasing the actual moisture content. Decreasing humidity in an air mass directly lowers the relative humidity. When air cools, it can also hold less moisture, which could result in condensation if it reaches saturation, but does not directly contribute to an increase in humidity unless accompanied by other factors that add moisture.