The Climate of India

India has tropical monsoon type of climate. It is greatly influenced by the presence of the Himalayas in the north as they block the cold the cold air masses from Central Asia. It is because of them only that the monsoons have a watershed in India.

   The Tropic of Cancer divides India into two almost equal climatic zones, namely, the northern zone and the southern zone. The warm temperate or the subtropical climate of the northern zone gives it cold winter seasons and the hot summer seasons.

   The southern tropical climatic zone is warmer than the north and does not have a clear-cut winter season.

   The northern zone does not have the midday sun vertically overhead during any part of the year; the southern zone has the midday sun almost vertically overhead at least twice every year.

Climate : Seasons in India

   In India, the year can be divided into four seasons, resulting from the monsoons which occur mainly due to the differential heating of land and movement of the sun's vertical rays.

   The vertical rays of the sun advance towards Tropic of Cancer from mid-March, due to which hot and dry weather arrives. As temperatures rise over most of northern and Central India, a vast trough of low pressure is created. The highest temperature experienced in South is in April while in North it is in May and June.

   This part of the year is marked by a dry spell and the north-western parts of the country experience hot, dry winds, called loo. In this period, the country also experience storms / dust storms at various places.

1.    Tornado like dust storms in Punjab and Haryana, called 'Andhis' in UP and 'Kalbaisakhis' in West Bengal.
They involve strong convectional movements causing some precipitation.

2.    The 'Norwesters' originate over the Chhotanagpur Plateau and blow in the north-east direction which brings about 50 cm of rainfall in Assam and about 10 cm rainfall in West Bengal and Orissa. This rainfall is very useful for Assam tea and spring rice crops of West Bengal.

3.    Similarly, 'Cherry Blossoms' are there in Karnataka, beneficial to coffee plantation and 'Mango showers' in elsewhere South India, which are beneficial to mango crops.

   This weather is followed by hot, wet weather from June to September. In May, the south - west monsoon sets in. The normal dates of onset of the monsoon are May 20 in the Andaman and Nicobar Islands, June 3 in the Konkan, June 15 in Kolkata and June 29 in Delhi.

   The south - west monsoon enters the country in two currents, one blowing over the Bay of Bengal and the other over the Arabian Sea. This monsoon causes rainfall over most of the country (except Tamil Nadu and Thar Desert area). The S.W monsoon entering from Western Ghats causes heavy rainfall over Kerala coast, but Tamil Nadu falls on the leeward side. In the Thar area, the winds blow parallel to the Aravallis and do not cause rain. The Bay of Bengal current causes heavy rainfall in the north east parts of the country and a part of it turns west along the Himalayas over the Indo-Gangetic plains causing rainfall in this region. But the Bay of Bengal current, by the time it reaches W Rajasthan, runs out of moisture.

   The Bay of Bengal branch after crossing the deltaic region enters the Khasi valley in Meghalaya and gets
entrapped in it due to funnel shape of the region. It strikes Cherrapunji in a perpendicular direction causing heavies rainfall in Mausingram (Approx. 1400 cm).

The North-East Monsoons:  From mid-Sept to mid-Dec, the monsoon retreats. As the sun's vertical rays start shifting towards the Tropic of Capricorn, the low pressure area starts moving south and winds finally start blowing from land to sea. This is called north-east monsoon. The withdrawal of monsoon is a much more gradual process than its onset. It causes rainfall in Tamil Nadu as the winds pick some moisture from Bay of Bengal. This explains the phenomenon why Tamil Nadu remains dry when the entire country receives rain and why it gets rain when practically the entire country is dry.

   The cold and dry weather starts in early December. In this, the average temperature in south is 24-25c, and while in the north is 10-15c. In the latter part of December and in January, the dry spell is broken by the westerly depressions (temperate cyclones) from Mediterranean Sea, which causes some rain in north-west India.

   Almost all the precipitation in India is caused by the monsoons and it is primarily orographic in nature. Cyclonic storms provide only a little rain, mainly in the north.