RAINFALL

• Rainfall refers to the amount of rain that an area receives over a period of time

• Rainfall is necessary to provide us with our supply of water

• Long periods without rain will cause droughts to occur. – Example: Sahel Desert (Africa)

• Persistent or continuous heavy rain may lead to floods that can damage property and claim lives. – Example: Low lying areas of Bangladesh

Effects of Rainfall

Land that is terribly dried up because of the lack of rain

High amounts of rainfall results in flooding

Measuring Rainfall

• Rainfall is measured using an instrument called a rain gauge

Funnel

Copper cylinder

Glass Bottle Outer Casing

Measuring Rainfall

• It consists of a funnel that collects and channels rainwater into a container

• The water collected in the glass jar is then poured into a measuring cylinder to show the reading

• It is measured in millimetres (mm) or centimetres (cm)

Formation of Rain

• When the Sun’s rays heats up the surface of the Earth, the air above it is warmed up.

• This causes the water from the land and oceans, seas and lakes to change into water vapor. This process is called evaporation.

• Plants also give out water vapor into the air through a process called transpiration

Formation of Rain• As the warm air rises, it begins to cool

• As soon as the air cools below a certain temperature, the water vapour that it is holding changes into very small water droplets

• This process is called condensation

Formation of Rain

• These tiny water droplets will remain suspended in the air

• When more water droplets are gathered together, clouds are formed.

• When the droplets of water become too big and heavy to float in the air, they will fall to the ground as rain. This process is termed precipitation.

Air cools

Clouds Condensation

Precipitation