There are four main seasons in India, viz. the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon.
The Cold Weather Season (Winter):
The winter season begins from mid-November and stays till February; in northern India. December and January are the coldest months in the northern part of India. The temperature ranges between 10°-15°C in the northern plains, while it ranges between 24°-25°C in Chennai.
The northeast trade winds prevail over the country in this season. As these winds blow from land to sea, most parts of the country experience a dry season.
The weather is usually marked by clear sky, low temperatures and low humidity and feeble variable winds.
The inflow of the cyclonic disturbances from the west and the northwest is a characteristic feature of the cold weather over the northern plains. These low-pressure systems originate over the Mediterranean Sea and Western Asia and move into India. They cause winter rains over the plains and snowfall in the mountains. The winter rainfall is in small amount but is very important for the rabi crop. This rainfall is locally known as mahawat.
The peninsular region does not get a well-defined winter because of the moderating influence of the sea.
The Hot Weather Season (Summer)
The summer season is from March to May. During this period, the global heat belt shifts towards north because of the apparent northward movement of the sun.
During summer, the temperatures rise and air pressure falls in the northern part of the country. Towards the end of May, an elongated low-pressure area develops in the region which extends from the Thar Desert in the northwest to Patna and Chhotanagpur in the east and southeast.
A characteristic feature of the hot weather season is the ‘loo’. These are strong, gusty, hot and dry winds which blow during the day over the north and northwestern India.
Dust storms are very common in northern India during the month of May. This is also the season of localized thunderstorms; accompanied by violent winds, torrential downpours, and hail.
Pre-monsoon showers are common towards the end of the summer season; especially in Kerala and Karnataka. They are often called ‘mango showers’ as they help in the early ripening of mangoes.
Advancing Monsoon (The Rainy Season)
The rainy season begins from early June.
The low-pressure condition over the northern plains intensifies at this time. It attracts the trade winds from the southern hemisphere. These south-east trade winds cross the equator and blow in a south-westerly direction to enter the Indian peninsula as the south-west monsoon. These winds bring abundant moisture to the subcontinent.
These winds blow at an average velocity of 30 km/h. The monsoon winds cover the country in about a month; barring the extreme north-west.
The windward side of the Western Ghats receives very heavy rainfall, early in the rainy season. The Deccan Plateau and parts of Madhya Pradesh also receive some rain, in spite of lying in the rain shadow area.
The north-eastern part of the country receives the maximum rainfall of this season. Mawsynram (Meghalaya) receives the highest average rainfall in the world.
Rainfall in the Ganga valley decreases from east to west. Rajasthan and parts of Gujarat get scanty rainfall.
Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. The monsoon rains take place only for a few days at a time and then come the rainless intervals. These breaks in the monsoon are because of the movement of the monsoon trough. The trough and its axis keep on moving northwards or southward due to various reasons. The movement of the monsoon trough determines the spatial distribution of rainfall.
The monsoon is famous for its uncertainties. It may cause heavy floods in one part of the country, and may be responsible for droughts in other part. Because of its uncertain behaviour, it sometimes disturbs the farming schedule in India. This affects millions of farmers all over the country.
Retreating Monsoon (The Transition Season)
During October-November, the sun apparently moves towards the south. During this period, the monsoon trough over the northern plains becomes weaker. The south-west monsoon winds weaken and start withdrawing gradually. The monsoon withdraws from the northern plains by the beginning of October.
The retreat of the monsoon is marked by clear skies and rise in temperature. While day temperatures are high, nights are cool and pleasant. Humidity is still present. High temperature and humidity, makes the weather quite uncomfortable during the day. This is commonly known as “October Heat”.
The temperature begins to fall rapidly in northern India by the second half of October. The low-pressure conditions over northwestern India move to the Bay of Bengal by early November. This shift leads to cyclonic depressions over the Andaman Sea. These cyclones usually cross the eastern coasts of India and cause heavy and widespread rain. These cyclones may also arrive at the Coasts of Orissa, West Bengal and Bangladesh. These cyclones contribute to the bulk of the rainfall of the Coromandel Coast.
DISTRIBUTION OF RAINFALL
The western coast and northeastern India receive over 400 cm of rainfall annually.
The annual rainfall is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Rainfall is also low in the interior of the Deccan Plateau and easth of the Sahyadris. The area around Leh also gets low rainfall.
The rest of the country gets moderate rainfall. Snowfall is restricted to the Himalayan region.
MONSOON AS A UNIFYING BOND
Although there are wide variations in weather patterns across India, the monsoon brings some unifying influences on India. The Indian landscape, its flora and fauna, etc. are highly influenced by the monsoon.
The entire agricultural calendar in India is governed by the monsoon. Most of the festivals in India are related to agricultural cycle. These festivals may be known by different names in different parts of the country, but their celebration is decided by the monsoon. It is also said that the river valleys which carry the rainwater also unite as a single river valley unit. Due to these reasons, monsoon is often a great unifying factor in India.