Defence
A line on a map joining places that receive equal amounts of rainfall (precipitation) is called an:
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Answer: Option C — Isohyet
Detailed Solution
An isohyet is a line on a map joining places that receive the same amount of rainfall (precipitation) during a given period, such as a year or a month. The word comes from the Greek "iso" (equal) and "hyetos" (rain).
How rainfall is measured:
- Rainfall is measured with a rain gauge, a simple instrument that collects rain in a funnel and measuring cylinder.
- It is expressed in millimetres or centimetres.
- Rainfall data from many stations are plotted on a map, and isohyets are drawn to show the pattern.
Uses of isohyet maps:
- They show the distribution of rainfall over a region.
- They help in planning agriculture, irrigation, water supply and flood control.
- They are used to calculate the average rainfall over a river basin.
Rainfall patterns in India shown by isohyets:
- The highest rainfall occurs on the windward side of the Western Ghats and in the north-eastern states.
- Mawsynram and Cherrapunji (Sohra) in Meghalaya receive more than 1,100 cm of rain a year, among the highest in the world.
- Western Rajasthan, Ladakh and parts of Gujarat receive very little rainfall, less than 25 cm a year in places such as Jaisalmer.
- The 100 cm isohyet is important in India; areas receiving more than 100 cm can grow rice, while drier areas grow millets and wheat with irrigation.
- The leeward (rain shadow) side of the Western Ghats, such as parts of interior Maharashtra and Karnataka, receives much less rain.
Main types of rainfall:
- Convectional rainfall: caused by rising hot, moist air, common near the Equator.
- Orographic (relief) rainfall: caused when moist air is forced to rise over mountains; most of India's monsoon rain is of this type.
- Cyclonic (frontal) rainfall: caused by the meeting of warm and cold air masses or by cyclones.
Why not the other options?
- ✗An isobar joins places of equal pressure.
- ✗An isogonal joins places of equal magnetic declination.
- ✗An isoseismal line joins places of equal earthquake intensity.
Quick tip
Remember: Isohyet = equal rainfall ("hyetos" = rain); measured by a rain gauge.
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