This is related to raising the condensation height. An air block is forced to rise from the ground under the action of external force, and the rising condensation height is when it reaches the saturation height. When the air is saturated, water vapor condenses, so the lifting condensation height is close to the cloud bottom height.

ZL= 123(T0-Td0) m

ZL is the condensation height of uplift, T0 is the ground temperature, and Td0 is the dew point of ground air.

The greater the relative humidity of the air block (the smaller the temperature dew point difference), the lower the lifting condensation height and the lower the cloud bottom.

In tropical and subtropical areas, the air is humid and the relative humidity is high, so the cloud bottom is very low.

Cumulus clouds are formed by air mass rising and water vapor condensation. The more water vapor in the air, the easier it is to form cumulus clouds.