Annual Rainfall in India
There is convectional rainfall on the southern slopes of the Himalayas, in the Western Ghats and in some other areas. In the north-western India, the rainfall is cyclonic in winter.
(1) Areas of Very Low Rainfall.
The rainfall is low and usually upto 25 cm annually and this is the area of the lowest rainfall in India. This area is of two types:
(a) Cold and Dry.
The area has a low temperature and remains below freezing point in winter. The temperature in summer is also around 10°C. It is situated north of the Himalayas’ high ranges in the Karakoram and in the area north of the Zanskar Range.
The reason is that the S.W Monsoons, which bring rainfall in summer, are rarely able to cross the Himayalas and enter this rain shadow area. It, therefore, remains cold and dry. Whatever rainfall it receives is available in July and August.
Another season in which it gets some rainfall extends from January to March. This rainfall is not brought by the monsoons but by western disturbances which reach this area from the Gulf of Oman and sometimes even from the Mediterranean Sea.
(b) Hot and Dry.
This area is hot and dry and lies in Western Gujarat (Kutchch) and in a narrow belt in western Rajasthan. The area sometimes extends to Southern Punjab and South-Western Haryana.
The monsoons fail to reach this area in any strength. The subsidence of air makes it the driest zone. Many stations like Banner, Jaisalmer, etc. do not record any rainfall sometimes for 3 to 4 years.
(2) Areas Lgw Rainfall.
The rainfall is low and ranges between 25-50 cm annually. It is also the area of the lowest reliability of rainfall. The following are the areas of low rainfall:
(a) Cold Northern Area.
This area is on the southern slopes and valleys of the Dcosai and Zanskar ranges oriented from north-west to south-east.
The rainfall which is ascribed to S.W Monsoons takes place in July and August and that due to western disturbances fall in March.
(b) Thar Belt.
This belt is situated mainly in the Thar Desert but extends from Gujarat, Western Rajasthan, Southern Punjab and South-Western Haryana. The rainfall varies from 25 to 50 cm.
The main rainy months are June, July, August and partly September. Some rainfall is received from December to March and even in April. This is due to western disturbances. The winter rainfall though small (one eighth of total) is very useful for rabi crops.
(c) Southern Belt.
It is a narrow belt (about 80-100 km wide) on the eastern slopes of the Western Ghats. This belt is parallel to the Western Ghats starting from the Satpura in the north, Maharashtra, S.W A.P, and Karnataka in the south.
The rainfall is received from June to September and even in October. As the area is situated in rainfall shadow zone of the Western Ghats, the rainfall is low but rainfall variability is high.
The rainfall in winter is not a phenomenon of this area as it is away from the area of Western Disturbances.
(3) Areas of Moderate Rainfall.
This area has an annual rainfall ranging from 50 to 100 cm. It is the largest belt and most extensive. The main areas are:
(a) Kashmir Valley .
It is the western mountainous tail area of S.W Monsoon winds. It gets rainfall in summer from S.W Monsoons and also in winter from Western Disturbances. The rainfall in winter is more and significant than that in the summer.
The winter rains from January to May amount to 40 cm while that in June and December (Pre-winter and Post-winter) totals 3-5 cm each. The S.W Monsoons provide a total of 16 cm rainfall from July to September.
(b) The Northern Plains.
It extends from southern U.P to eastern Punjab and Haryana. The rainfall was higher in these areas but deforestation by man has resulted in low annual rainfall.
The main rainy months are June to September and another spell of Western Disturbances from December to March also causes rainfall.
(c) Malwa Plateau.
This lies between the Aravalis in the west to Vindhyas in the south-east in Rajasthan and western M.P The rainfall is largely from June to September. There is no rainfall in winter worth the name.
(d) Southern Peninsular Area.
This area lies in the eastern Maharashtra, Karnataka, A.P and most of Tamil Nadu. In this area the northern part receives summer rainfall from June to September but in the southern part there are two maxima of rainfall.
The southern part has rainfall from July to November and the other from April to May. The S.W Monsoons in summer and the north-east winds in winter provide rainfall.
(4) Areas of High Rainfall.
Rainfall is 100 to 200 cm per year. Such areas are not necessarily contiguous. They are found in different parts of India.
One common thing about them is that rainfall is dominantly influenced by S.W Monsoons.
(a) The Northern Belt.
From Jammu Hills, H.P, the northern belt in Uttaranchal (including the Himalayan areas), Bihar and West Bengal, the rainfall decreases continuously from the east to west as the S.W Monsoons are depleted of its humidity.
This rainfall is responsible for high fertility of the soil and for raising different crops. This area has high density of population due to fertile land.
(b) Northern Peninsular Belt.
It covers Orissa, northern A.P, eastern Maharashtra and most of southern M.P. The cyclones which form in the Bay of Bengal move into Orissa and cause rainfall in the surrounding areas.
However, the rainfall decreases from the east coast towards the interior. The rainfall is received from June to October.
(c) Small Coastal T.N. Belt.
This area extends from Karaikal to Chennai and is very narrow mostly confined to the coast.
The rainfall is received mainly from May to September from S.W Monsoons and during winter from the dry winds which come from the north-east of India but pick up moisture enroute over Bay of Bengal.
(d) Eastern Slopes of Western Ghats.
It is an area adjoining the Western Ghats running parallel to them. This is a narrow belt getting spill-over rainfall from the Western Ghats.
The rainfall is largely from May to September. Winter rainfall is almost absent.
(e) North-east Rainfall Area.
It includes Assam Valley, Mikir Hills and parts of India, east of Bangladesh in Tripura and the adjoining states. The rainfall is confined to April-September months. It is far away from the Western Disturbances and hence the winters are dry.
(5) Area of Very High Rainfall.
Rainfall is above 200 cm per year. There are two such areas:
(a) Western Ghats .
The narrow Western Ghats and the western slopes upto the coast are exposed to the oncoming south-west monsoon winds.
The rainfall is heavy. In the northern part, the maximum rainfall is from June to September but in the southern part, the maxima are two – one in June and the other in October.
(b) North-Eastern India.
It covers lower and middle Assam valley. Garo, Khasi, Jaintia Hill complex, Shillong Plateau, Arunachal and northern W Bengal.
The highest rainfall, of about 1,080 cm is received at Cherrapunji on Shillong Plateau. This was considered to be the place of highest rainfall in the world but now Mawsinram, a place close by, is reported to have been receiving the highest amount of rainfall in the world.
Situated in funnel like hills, the monsoon winds have intense condensation, resulting in heavy rainfall.
The rainy months are from May to September but in the northern areas, the rainy months are from April to September. The rainfall is attributed to S.W Monsoon winds, which strike the hills and mountains straight in the north-east India.