Which factor directly affects the base altitude of cumulus clouds?

The base altitude of cumulus clouds is primarily influenced by humidity. More specifically, it is related to the amount of moisture present in the atmosphere. When air rises, it cools, and as it cools, the capacity of air to hold moisture decreases. Once the air reaches a certain temperature known as the dew point, the water vapor condenses into tiny water droplets, forming clouds.

This process means that the greater the humidity in the air, the higher the dew point will be, and consequently, the base altitude of cumulus clouds will also be higher. Conversely, if the air is less humid, the dew point is lower, and the clouds will form at a lower altitude.

Temperature does play a role indirectly, as warmer air can hold more moisture, but it is the actual humidity that directly determines how and when the condensation occurs, thereby affecting the cloud base altitude specifically. Therefore, humidity is the key factor that directly influences the base altitude of cumulus clouds.