Types Of Rainfall

Rainfall occurs when air bearing moisture rises into the atmosphere, followed by cooling, condensation and finally precipitation. However, rains may occur naturally due to three reasons such as when the air mass gets obstructed by a relief barrier such as a mountain, or an uplift due to convection currents or due to a cyclone in the tropical regions. There is an imaginary line, known as isohyets, which joins regions that experience equal amount of rainfall. There are three major types of rainfall, namely convectional rainfall, relief rainfall and frontal rainfall. Convective precipitation is much greater in intensity but lasts for shorter periods as compared to frontal rainfalls. However, the physical feature of precipitation may also be divided into either liquid or solid forms. Rain and drizzle are the examples of liquid forms of precipitation. When rain or drizzle freeze as they come in contact with a subfreezing air mass, it leads to freezing rain or freezing drizzle. There are several frozen forms of precipitation as well, ranging from snow, sleet, hail to ice needles. To learn more about precipitation, particularly rainfall, read the lines below.

Different Types Of Rainfall

Convectional Rainfall
The heating of the surface of the earth by the sun is the primary cause of convectional rainfalls. Due to sunrays, the water on the surface of the earth evaporates and turns into lightweight, moist air which begins to rise upwards.  As the air ascends in atmosphere, it cools down considerably and gradually approaches the condensation point. As the water vapor condenses, it acquires a liquid form again. This condensation leads to the formation of clouds high up in the atmosphere. As the clouds continue to accumulate, rain occurs due to the increasing weight of the water droplets.

Frontal Rainfall
This particular type of rainfall is most common in regions such as the United Kingdom. According to the statistics, the amount of frontal rainfall in the United Kingdom exceeds the convection rainfall. When a warm and a cold body of air collide with each other, frontal rainfalls occur. As the mass of warm air strikes a mass of cold air, the warm air, due to its light weight, rises above the colder mass of air which is much heavier and denser comparatively. As the warm air rises, it begins to cool down and once it reaches the point of dew formation, the air mass begins to condense and clouds are formed. This results in precipitation and the subsequent rain falls across a large area.

Relief Rainfall
Relief Rainfall, or the orographic rainfall, occurs when moist air begins to rise over mountains or hills. When the air begins to rise in the atmosphere, it reaches a condensation point where water vapors convert back to water droplets and, consequently, clouds are formed. As the clouds accumulate, their size grows and it leads to rain. The relief rains are common occurrences in the coastal areas encompassed by many great hills. The onshore wind with moisture content collides with the mountains/hills and begins to descend along the slope and starts to cool down. When the air temperature falls to its dew point, water vapor condenses to form clouds. As the clouds keep accumulating in this fashion, the water droplets become heavy and rain occurs.

Other Types Of Rainfall 

Acid Rain
Acid rain is a type of precipitation that is quite acidic in nature, which means that the precipitation contains high levels of hydrogen ions i.e. a low pH value. It can have extremely deleterious effects on the plant and animal life of the region. Sulfur dioxide and nitrogen oxides emitted in the atmosphere, react with the water molecules to produce acids which come down in the form of such acid rains. This type of rain acidifies lakes and streams and contributes to the damage of trees at high elevations. Acid rain can also be harmful to the paints on the buildings and also harm the overall health of various constructions. Around 70 percent of sulfur dioxide and 30 percent of nitrogen oxides are emitted from the electric power plants alone. Vehicles also eject a considerable amount of nitrogen oxides into the atmosphere thereby contributing towards that harmful phenomenon.

Hail Rain
Rain occurs when accumulating cloud masses become too heavy. The water droplets, at times, coalesce to form small ice pellets which start to freeze when winds drag these pellets and droplets into the colder regions at the higher levels of the cloud. When the clouds carrying these pellets get heavy, hail occurs. This form of rainfall can be anything from amusing to life-threatening, depending upon the size and speed of the pellets.

Apart from natural types of rainfalls such as convectional, frontal and relief, others like acid rains which occur due to air pollution have also been encompassed in the above written article. We hope you now know the types of rainfall and the reasons behind their occurrence.