HKDSE Geography/E2/Precipitation

Classification

Types of precipitation include:

• Rain
• Hail
• Sleet (not present in Hong Kong)
• Snow (not present in Hong Kong)

General Steps

1. Warm air converges, rises up, expands to form uprising air currents.
2. As warm air rises, it falls by 6 degrees Celsius per 1000 m. Relative humidity increase.
3. At the condensation level, relative humidity reaches 100%, or dew point. The air is said to be saturated.
4. Excess water vapour condenses on condensation nuclei. Water droplets form.
5. Water droplets accumulate to form clouds.
6. When the clouds are too heavy to support, the droplets fall as rain.
7. Sometimes accompanied by thunderstorms or lightning.

Three Types of Rain

For each of the following types of rain, warm air rises for different reasons.

Frontal Rain

• A cold front occurs when a warm air mass and a cold air mass meet.
• The warm air mass is forced up by the cold air mass.