Precipitation

Precipitation is any liquid or frozen water which forms in the atmosphere and falls back to the surface of the Earth. It comes in many forms, such as rain, sleet, and snow, however, it all comes from the same general process. Along with the processes of evaporation and condensation, precipitation is amongst the three major parts of the global water cycle that are important for the sustainability of life on Earth. In this article, we will learn about the precipitation meaning, what are the different forms of precipitation, what is the process of precipitation, classification of precipitation, and examples of precipitation in detail. Let us first have a look at what is precipitation.

Precipitation Definition

Precipitation is defined as the formation of a solid from a solution. When the reaction occurs in a liquid solution, the solid that is formed is called a precipitate. The chemical which causes the solid to form is called a precipitant.

Consider, for example, precipitation occurs when a part of the atmosphere saturates itself with water vapour and with the right temperature, it condenses and precipitates. The two processes that make the air saturated are the cooling of air molecules in the atmosphere and the addition of water vapour.

Precipitation Process

Let us now look at what is the process of precipitation.

Precipitation forms in the clouds when the water vapour condenses into larger droplets of water in the atmosphere. When these drops are heavy enough, they fall to the surface of the Earth. If a cloud is colder, just as it would be at higher altitudes, the water droplets may freeze and form into ice. These ice crystals then fall to the Earth as snow, hail, or rain, depending on the temperature within the cloud and at the surface of the Earth. Most of the rain actually begins as snow high in the clouds. As the snowflakes keep falling through the warmer air, they become raindrops and eventually fall on Earth. 

Particles of dust or smoke in the atmosphere are important for the precipitation process. These particles are called condensation nuclei and they provide a surface for water vapour to condense upon. This, in turn, helps water droplets gather together and become large enough to fall to the Earth.


Let us now look at what are the different forms of precipitation.

Forms of Precipitation

The different forms of precipitation are as follows:

1. Rain

Rain is a form of precipitation which is in the form of water drops of a size that is larger than 0.5mm. The maximum raindrop size is about 6mm. Drops of larger size break up into smaller drops as it falls down on the Earth’s surface.

Rainfall is the predominant form of precipitation and therefore, the term precipitation is used synonymously with rainfall. The magnitude of the rainfall shows high temporal and spatial variation. This variation causes the occurrence of hydrologic extremes like floods and droughts.

2. Snow

Snow consists of ice crystals in a flaky form, having an average density of 0.1g/cc. It is also an important form of precipitation that usually forms in colder climates and higher altitudes.

3. Drizzle

Drizzle is a fine sprinkle of tiny water droplets that have a size less than 0.5mm and intensity greater than 1mm/h. The tiny drops that form a drizzle appear floating in the air.

4. Glaze or Freezing Rain

The glaze is formed when rain or drizzle comes in direct contact with the cold ground at around 0 degrees celsius. This water drops freeze to form an ice coating known as glaze.

5. Sleet

Sleet is frozen raindrops that are formed when rainfall passes through the air in the atmosphere at subfreezing temperatures.

6. Hail

Hail is a kind of showery precipitation in the form of pellets or lumps that have a size greater than 8mm. Hail occurs during the violent thunderstorms.

These are the examples of precipitation. Let us now look at what are the different types of precipitation.

Types of Precipitation

Precipitation occurs when the moist air mass undergoes the process of condensation. This process occurs when the air is cooled and saturated with the same moisture amount. This process of cooling the air mass occurs only when the air mass moves up to the higher altitudes. The air mass can be lifted to higher altitudes primarily by three methods based on which there are three different types of precipitation which are as follows:

  1. Cyclonic Precipitation

  2. Convective Precipitation

  3. Orographic Precipitation

1. Cyclonic Precipitation

A cyclone is a region in the atmosphere that has a large low pressure having circular wind motion. The cyclonic precipitation is caused due to the movement of moist air mass to this region by the difference in pressure. Cyclonic precipitation is two types: frontal and non-frontal precipitation.


Frontal Precipitation

A frontal is known as the hot moist air mass boundary. This precipitation is caused due to the expansion of air near the frontal surface.


Non-Frontal Precipitation

This is a cold moist air mass boundary which moves and results in precipitation.

2. Convective Precipitation

The air above the land area gets heated up due to some cause. Most of this warmer air rises up, cools and precipitates. Convective precipitation is showery by nature. This type of precipitation occurs in varying intensities.

3. Orographic Precipitation

Moving air masses have a chance to strike barriers such as mountains. Once they strike, they rise up causing condensation and precipitation. The precipitation that occurs is greater in the windward side of the barrier when compared to the leeward side of the barrier.

FAQ (Frequently Asked Questions)

1. What is the Definition of Precipitation?

Precipitation is defined as any type of water which forms in the Earth's atmosphere and drops onto the surface of the Earth. Water vapour and droplets of water suspended in the air build up in the atmosphere before precipitating. 

2. What Causes Precipitation to Occur?

Precipitation is caused by the condensation of water vapours in the air mass. The ascending air mass having a sufficient amount of water vapours turns saturated due to adiabatic cooling. Condensation of water vapours then leads to the formation of clouds. These clouds, when condensed, leads to different forms of precipitation.