The document discusses different types of rainfall. It explains that convectional rainfall occurs when the sun heats the earth's surface, warming the air which rises through convection. As the air rises and cools, water vapor condenses to form clouds and rain. Frontal rainfall happens when a warm air mass forces under a cold air mass, causing the warm air to rise over the cold air where it cools and condenses. Orographic rainfall is produced when warm moist air is forced upward by upland areas, expanding and cooling to produce rain.

1. Geography
Rainfall TypesRainfall Types
Aim :
Why does it rain?

2. Geography
Why does it rain?Why does it rain?
Try to guess which word fits?
The sun heats the earth’s surface and in turn the
air above it becomes cool/warmcool/warm and it rises/fallsrises/falls
by the process of confusion/convectionconfusion/convection. As it
falls/risesfalls/rises, the air warms/coolswarms/cools until the water
vapour evaporates/condensesevaporates/condenses, forming thick/thinthick/thin
clouds.

3. Geography
• During summer days the earth’s surface can becomes very hot.
• This can cause an intense warming of the air making it very
buoyant.
• The air rises quickly.
• As it does so it expands and cools. The air can no longer hold
• the moisture; condensation takes place and rain forms.
• The cool air then falls and
• is caught and dragged back
• upward by more rising air
• forming a convection cell.
Convectional RainConvectional Rain

4. Geography
Frontal RainFrontal Rain
• A warm air mass tries to force into a
cold air mass.
• The warm air is lighter and less dense
than the cold air and so is forced to rise
over it.
• As the warm air rises it expands and
cools and so rain forms.

5. Geography
This line
represents the
front separating
warm air from
cold air
Rain
Cumulus cloud
Warm air
Warm air rises over cold air;
it expands and cools, condenses,
clouds and rain form
Warm air
Cool air

6. Geography
Orographic (Relief) RainOrographic (Relief) Rain
• Upland areas force the warm moist air
upward, where it cools.
• As the warm air rises it expands and
cools, condensation takes place and
rain forms.
• The rain is often heavy and prolonged.

7. Geography
Sea
Moist
wind
Rain
Dry wind
Little or no rain
Pressureincreases
Pressuredecreases When air rises the
pressure on it decreases;
the expands and cools
When the air
descends the
pressure on it
increases; the
air contracts
and warms