Indian Climate: Seasons

In general, Indian climate is monsoonal in nature. Primarily there are four seasons in India.

• Summer season
• Southwest Monsoon season
• Retreating monsoon season
• Winter season

SUMMER SEASON

• It extends from March to mid-June.
• Sun’s apparent movement is towards tropic of cancer.
• The hot weather season in south India is mild and not so intense as found in north India (proximity of South India to the oceans).
• Isotherms parallel to the coast confirms that temperature does not decrease from north to south rather it increases from the coast to the interior.
• Hot winds ‘Loo’ blows across northern plains.
• During pre-monsoon phases hot dry land breeze meets the humid sea breeze leading to violent winds, rainfall and hailstorms. These winds have certain local names as well:

Local winds	Region	Characteristics
Nor Westers	Eastern India	Useful for jute, tea and rice cultivation
Kalbaisakhi	West Bengal	Norwesters in Bengal
Bardoli cheerha	Assam	Norwesters in Assam
Mango shower	Kerala + coastal areas of Karnataka	Useful for early ripening of mangoes
Blossom showers	Kerala + nearby areas	Useful for coffee flowers

SOUTH-WEST MONSOON SEASON

According to IMD, June, July, August and September are the monsoon months. The monsoon approaches India through Arabian sea branch as well as Bay of Bengal branch.

• The Arabian Sea branch first reaches Andaman and Nicobar coast on 25^th May and then hits Kerala coast on 1^st June.
• It splits into three branches:

1. It’s one branch is obstructed by the Western Ghats. These winds climb the slopes of the Western Ghats and cause rainfall over windward sides. The leeward sides (rain shadow areas) remain dry.
2. Another branch strikes the coast north of Mumbai. Moving along the Narmada and Tapi river valleys, these winds cause rainfall in extensive areas of central India; Chhotanagpur plateau.
3. A third branch of this monsoon wind strikes the Saurashtra Peninsula and the Kachchh, passing over west Rajasthan and along the Aravalli, causing only a scanty rainfall. In Punjab and Haryana, it joins the Bay of Bengal branch. These two branches, reinforced by each other, cause rains in the western Himalayas.

• Arabian sea branch is stronger than Bay of Bengal branch as Arabian sea branch is responsible for 65% humidity.
• The Bay of Bengal branch gets deflected from Arakan Hills towards the Indian subcontinent and hence monsoon enters West Bengal and Bangladesh from south and southeast.
• From here, this branch splits into two under the influence of the Himalayas and the thermal low in northwest India.
• It’s one branch moves westward along the Ganga plains reaching as far as the Punjab plains. The other branch moves up the Brahmaputra valley in the north and the northeast, causing widespread rains.
• The sudden arrival of the SW monsoon in India is called as Burst of monsoon.

RETREATING MONSOON SEASON

• This is also known as autumn season.
• During the months of October and November, southwest monsoon becomes weak as the low-pressure trough starts moving southward.
• The monsoon retreats from Rajasthan, Gujarat, Western Ganga plain and the Central Highlands by the end of the month.
• By the beginning of October, the low pressure covers northern parts of the Bay of Bengal and by middle of December, the centre of low pressure is completely removed from the Peninsula.
• The retreating southwest monsoon season is marked by clear skies , rise in temperature and humidity, leading to oppressive weather. This is commonly known as the ‘October heat.’
• The widespread rain in this season is associated with the passage of cyclonic depressions which originate over the Andaman Sea and manage to cross the eastern coast of the southern Peninsula.

WINTER SEASON

• It sets in by mid-November in northern India. December and January are the coldest months in the northern plain. The mean daily temperature remains below 21°C over most parts of northern India.
• The high pressure exists over northern plains and thus as a result, winds start blowing from north-western high-pressure zone to the low air pressure zone over the Indian Ocean in the south.
• Pressure gradient is lower hence the winds speeds are also lower.
• During this season, temperate cyclone (shallow depressions) rising from Mediterranean Sea enters India with the help of westerly Jetstream. This is known as western disturbances and is helpful for Rabi crops.