Precipitation.
Humidity is the amount of water vapour in the air. This is produced by the evaporation
of water from oceans, lakes, rivers, wetlands and plants.
When water evapour in the air cools, it condenses. In other words, it becomes liquid and
forms little drops. These droplets form clouds.
When the droplets are small, they remain suspended in the atmosphere. But they often
become colder and their size and weight increases When they become too heavy to
remain suspended in the air, they fall to the Earth’s surface. We call this precipitation,
which may be rain, snow or hail.
Factors affecting precipitation.
Different areas of the Earth’s surface receive different amounts of precipitation.
Latitude: it rain more in the areas near the equator than in the temperature
zones and polar regions. The temperature is higher near the Equator so there is
more evaporation.
Altitude: it rains more in high areas than in low areas.
Level of humidity: it rains more on the coast than inland. Seas are a source of
humidity.
Precipitation is measured in millimeters (mm) per square matre.