In this essay we will discuss about the meaning and types of precipitation.
Essay on Precipitation:
The evaporated water from the surfaces of streams, rivers, sea, ponds, wet surfaces, trees, and plants etc. get collected in the atmosphere and behave like a gas. Under the normal conditions of temperature and pressure, this water vapour obeys the various gas laws (i.e. Boyle’s law, Charle’s law etc.) With the increase in the evaporation, the quantity of atmospheric vapour goes on increasing.
The atmosphere can hold the vapour up to its saturation point, after which it gets condensed on the surfaces. This condensation is the precipitation in various forms as described in the preceding article. The evaporated water thus again returned to the earth’s surface in any of these forms, is known as precipitation.
The major part of the precipitation occurs in the form of rain whereas small part in the form of snow. During the design of hydrological works other forms of precipitation such as hail, sleet, mist etc. are ignored, as their quantities are very small.
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It is the primary source of all water available on the earth and includes rainfall, snowfall, hail and sleet. All water sources receive their supply of water from the precipitation.
The water of precipitation further goes off in the following ways:
(i) Run-Off:
After precipitation, a portion of its water flows over the ground in the form of rivers and streams and some water flows towards lakes and ponds and is collected there.
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(ii) Percolation:
A portion of precipitation percolates in the ground and is stored there in the form of sub-soil or ground water.
(iii) Evaporation:
Some portion of the precipitation is also evaporated from the lakes, rivers, reservoirs and wet surfaces in the form of vapour due to sun’s heat. The portion so evaporated is called evaporation.
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(iv) Transpiration:
The roots of the trees absorb water from the ground and some portion of it evaporates in the atmosphere through leaves in the form of transpiration.
Essay on the Types of Precipitation:
There are three different methods by which the air mass gets lifted, so as to cause cooling and condensation of the atmospheric water vapour and the subsequent precipitation mainly in the form of rain or sometimes under special conditions as snow, hail, sleet, etc.
Depending upon the way in which the air is cooled so as to cause precipitation, we can have three kinds of precipitation, as given below:
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(i) Cyclonic Precipitation:
Such type of precipitation is caused by the lifting of an air mass due to the pressure difference. If low pressure occurs in an area air will flow horizontally from the surrounding area, causing the air in the low pressure area to lift. The precipitation that results is called “Non-frontal cyclonic precipitation.”
If one air mass lifts over another air mass, the precipitation is called “frontal cyclonic precipitation.” Warm air is lifted when cooler air settles down. Due to the rotary motion of the earth about its own axis, the air which rushes horizontally to fill the low pressure area is converted into whirlming mass known as ‘cyclon’.
The cyclone is a very large mass of air ranging from 800 to 1600 metre in diameter and moving with a velocity of about 50 km/hr. The central portion of this cyclone, where the pressure is low acts like a chimney, through which the air gets lifted, expands, cools and finally gets condensed, causing precipitation, which can occur in the form of drizzle, intermittent rain or steady rain. Most of the rains in the central part of the United States, and the most of the winter rains in Haryana and Punjab in India, occurs due to cyclones.
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(ii) Convective Precipitation:
Due to the upward movement of the air that is warmer takes place. Generally, this type of precipitation occurs in such places where the ground surface gets heated unequally. This situation may come where one place of the ground is covered with trees or grass and the adjoining place is open and pucca like houses, roads, hills etc. The warmer air will have tendency to rise upward, whereas the cooler air will move to fill its gap. Such precipitation occurs for short duration, in the form of showers of high intensity.
(iii) Orographic Precipitation:
For most of the heavy rains in most part of India, such type of precipitation is responsible. Orographic precipitation is caused by air masses which strike some natural topographic barriers like slopy mountains, and cannot move forward, rises up, causing condensation and precipitation.
But in such type of precipitation, greatest amount of precipitation falls on the winds ward side, and the leeward side often has very little precipitation. The rainfall is composed by showers and steady rainfall. The southern slope of Himalayas in India is the example of such type of barriers.