Rainfall is the measure of precipitation received in a particular region during a period. The precipitation involves rain, snowfall, sleet, haze, etc. Rainfalls are of several types. Precipitation is the process in which the air gets soaked with water vapour and hence starts to pour as it cannot sustain the water vapour in the gaseous form any further. There are several types of precipitation – Liquid, Freezing, and Frozen.
Precipitation in the liquid form is known as “Rainfall”. There are many types of rainfall based on the origin or the kind of moisture burdened air.
Different types of rainfall are:
This type of rainfall occurs in areas of high temperature, particularly during summer months. When solar intensity increases during the afternoon, large-scale moisture evaporates rapidly, and they condense at high altitudes, forming intensive rainfall normally restricted to a small region. This rainfall is of short duration and will subside as fast as it started.
Example: In India, this type of rainfall can be seen in plains, especially in northern India during the summer months.
- When the air gets heated, it becomes light, and so it rises in convection currents.
- As the air rises, it expands and drops the temperature, and gradually, condensation takes place and forms as cumulus clouds.
- Heavy rainfall with lightning and thunder takes place which does not last long.
- Such rain is usually in the summer or the hotter part of the day.
- This type of rainfall usually takes place in the equatorial regions and internal components of the continents, specifically in the northern hemisphere.
- This rainfall is related to hail and graupel.
This form of rainfall happens at the foot and windward side of a mountain. As moisture-laden clouds approach high mountains, they ascend along the slope, and as a result, they condense and form rainfall. This rainfall usually results in some areas on the other side of the mountain become drought-prone.
Example: The western ghats are the perfect example of orographic rainfall in India. Meghalaya hills and foothills of the Himalayas are known for this kind of rain.
- When the saturated air clouds come on the way of a mountain, the wind current forces the clouds to rise.
- The rising air expands, and gradually the temperature falls, and the moisture gets condensed.
- The main characteristics of this type of rainfall are that the windward slopes get more rainfall.
- After pouring rain on the windward side when the winds reach the other slope, they drop out, and hence their temperature increases.
- And then their ability to take in moisture increases and so these leeward slopes remain dry and rainless.
- The region located on the leeward side is known as the rain-shadow area.
Frontal or Cyclonic rainfall:
Frontal rainfall occurs when pressure difference creates storms and cyclones. The cyclonic system will bring a large amount of rain as it approaches land. Similarly, temperate cyclones form rainfall at the border of warm and cold fronts.
Example: Coastal India, especially the Bay of Bengal states, receives frontal rainfall.
- Cyclonic activities cause cyclonic or frontal rainfall which occurs along the fronts of the cyclone.
- When two chunks of air of different density, temperature, and humidity meet then this kind of precipitation happens.
- The layer separating them is known as the front.
- A warm front and the cold front are the two sides of the front.
- At the warm front, the warm and lighter wind increases slightly over the denser cold air.
- As the warm air rises, it cools, and hence the moisture content present in it condenses to form clouds.
- This rain falls gradually for a few hours to a few days.
There are several threats as well due to the excessive rainfall
Hazards due to excessive rain are:
- Flash floods: The most significant threat through excessive rainfall is the occurrence of flash floods. The high amount of rain in a short duration will create destruction of property and life.
- Landslides: Landslides become regular if rainfall increases its limits. The landslides may destroy forests, properties, and even life.
Rain is a form of precipitation that forms as a result of the condensation of the clouds and the water vapour content in it. There are different types of rainfall which are categorised based on the origin- cyclonic or frontal rainfall, orographic rainfall, and conventional rainfall.
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