Rainfall is the amount of water falling in rain, snow, etc., within a given time and area, usually expressed as a hypothetical depth of coverage.
Three types of rainfall are:
Convectional rainfall, this type of rainfall occur due to thermal convention due to heating of ground surface.When the land warms up, it heats the air above it. This causes the air to expand and rise. As the air rises it cools and condenses. If this process continues then rain will fall.
The following precondition must exist for this type of rainfall to occur
- Abundant supply of moisture through evaporation to air so that relative humidity becomes high
- Intense heating of the ground surface through incoming shortwave electromagnetic solar radiation
Convectional rainfall occur for very short duration but occur in form of heavy showers. It makes cumulonimbus clouds.
Orographic or relief rainfall, this is type of rainfall which occur when air has blown over the sea and is then being forced up over an area of high land. This causes air to cool and moisture in the air to condense into rainfall
The precondition for for formation of orographic rainfall are
- There should be a mountain barrier across the wind direction, so that the moist air is forced on obstruction to move upward
- There should be sufficient moisture in the air
- The mountain must be high enough to block the incoming moist air
Once over the top of the mountain the air will usually drop down the other side, warming as it does so. This means it has a greater ability to carry water moisture and so there is little rain on the far side of the mountain. This area is called the rain shadow.
Cyclonic or frontal rainfall, type of rainfall which occur when warmer air is forced to rise over cold air. The moist warm air condenses as it cool which causes cloud and rain. Frontal rain produces a variety of clouds, which bring moderate to heavy rainfall.