Rain

Rain is a type of precipitation that occurs when water vapor in the Earth's atmosphere condenses into visible droplets of water, which then fall to the ground. It plays a crucial role in the water cycle, and is responsible for depositing most of the fresh water on the Earth.

Formation

Rain forms when separate drops of water fall to the Earth's surface from clouds. Not all rain reaches the surface; some evaporates while falling through dry air. This is termed virga, a phenomenon which is often seen in hot, dry desert regions.

Types of Rain

There are three main types of rain, which are classified by how they form. These include:

• Stratiform rain: This type of rain occurs when there is uniform cloud coverage and weak vertical air motion. It is characterized by its steady, light to moderate intensity.

• Convective rain: This type of rain is formed by convective clouds, usually in the form of showers or thunderstorms. It is characterized by its variable intensity, which can range from light to heavy.

• Orographic rain: This type of rain occurs when moist air is forced upwards over elevated terrain, such as mountains. It is characterized by its persistence over a particular area.

Effects

Rain has a number of effects on the environment and on human activity. These include:

• Agriculture: Rain provides the water needed for plants to grow, and is therefore crucial for agriculture. However, too much rain can lead to flooding and crop damage.

• Water supply: Rain replenishes freshwater in rivers and lakes, supplying much of the water needed by humans for drinking and irrigation.

• Weathering: Rain, particularly acid rain, can cause erosion and weathering of rocks and buildings.

Measurement

Rain is measured in units of length per unit time, typically in millimeters per hour. The main tools used to measure rain are the rain gauge, which collects rain in a graduated cylinder, and the weather radar, which uses the reflection of a radio wave to measure the amount of rain falling.

See also

• Precipitation
• Water cycle
• Cloud
• Weather