Rainfall occurs when moist air is forced to rise. As it rises it cools and condensation of water vapour takes place. The water droplets increase in size until gravity forces them to fall to the ground as rainfall. There are three main reasons why moist air is forced to rise: a) changes in relief, b) convectional currents, and c) differences in air pressure.
a) Relief Rain.
This diagram shows how a change in relief can cause rainfall.
1. Rearrange the relief_rainfall_dominoes to give the correct explanation for relief rainfall in Morocco (see map below).
3. Explain why the cumulonimbus cloud at the cold front is taller and gives heavier rain than the nimbostratus cloud at the warm front.