Rainfall Classification by India Meteorological Department (IMD)

02 Dec 2021 Rainfall Classification by India Meteorological Department (IMD)

• According to IMD data, the average rainfall in the month of August was recorded 24 percent less in India, due to which there is a possibility of a decrease of 9 percent in the entire monsoon period.

Background:

• India Meteorological Department was established in the year 1875. It is the main agency dealing with meteorological information, weather forecasting and seismology.  It is an agency of the Ministry of Earth Sciences, Government of India.
• The long period average of rainfall for each common region of the country has been determined by IMD at the all India level, whose prescribed range is from 71.6 cm to 143.83 cm.

Rainfall Classification by IMD:

 On the basis of the amount of rainfall at the all India level, it is divided into five distribution categories-

• Near Normal: When the percentage of actual rainfall is 10 percent of the Long Period Average (LPA) of rainfall, ie between 96-104 percent of the LPA.
• Below Normal: When the actual rainfall is less than 10 per cent of the LPA i.e. between 90-96 per cent of the LPA.
• Above normal: When the actual rainfall is 104-110 per cent of the LPA.
• Deficiency: When the actual rainfall level is less than 90% of the LPA.
• Excess: When the actual rainfall level is more than 110 per cent of the LPA.
• In India, about 50 percent of the area is unirrigated (based on rainwater) and 70 percent of the annual rainfall is received from the monsoon, so normalization of monsoon becomes important for agriculture and economic development.

The main factors affecting the Indian monsoon:

• El Nino: El Nino causes drought conditions in India while La Nino causes excessive rainfall.
• Indian Ocean Dipole (IOD): It affects the Indian monsoon. There is a positive effect on monsoon rainfall during positive IOD and adverse effect on monsoon rainfall during negative IOD.
• Inequality in the amount, intensity and distribution of rainfall has increased as a result of climate change.

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