The average rainfall in India is 125 cm. The South-west monsoon constituted 75% of the total rainfall (June to September), 13% of it by north-east monsoon (October to December), 10% of it by pre monsoon cyclonic rainfall (mainly in April and May and 2% of it by western disturbances (December to February).
The western coast and North-Eastern India receive over about 400 cm of rainfall annually. However, it is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Rainfall is equally low in the interior of the Deccan plateau, and east of the Sahyadris. A third area of low precipitation is around Leh in Jammu and Kashmir. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region. Owing to the nature of monsoons, the annual rainfall is highly variable from year to year. Variability is high in the regions of low rainfall such as parts of Rajasthan, Gujarat and the leeward side of the Western Ghats. As such, while areas of high rainfall are liable to be affected by floods, areas of low rainfall are drought-prone.
Fig: Indian Seasonal Rainfall
• Areas of heavy rainfall: Those areas of India where there is more than 200 cm rainfall. There are three such main areas in India:
I. The western slopes of the Western Ghats.
II. The north-east India (except Tripura and Manipur)
III. The Andaman and Nicobar Islands.
• Areas of scanty rainfall: These areas receive less than 50 cm average annual rainfall. There are three such areas in India:
I. Northern Gujarat, western Rajasthan and the southern parts of Punjab-Haryana
II. The rain-shadow area of the Western Ghats
III. The desert of Ladakh
There is too much variability in the monsoon rainfall. This variability is less in the heavy rainfall areas any more in the areas of scanty rainfall. Variability means the deviation of the rainfall recorded in a certain year at a certain place from the average annual rainfall at that place.
• The bursting of monsoon: When low pressure is formed in the whole northern India in the beginning of June, there is rainfall with sudden thunderstorm and lightning in the form of southwest monsoon towards the Indian Ocean. It is known as the ‘bursting of monsoon'.