Seasons in India – UPSC Indian Geography Notes

India experiences a distinctive annual climatic cycle, comprising four seasons: the cold weather season, the hot weather season, the southwest monsoon season, and the retreating monsoon season. Meteorologists categorize India’s climatic conditions based on this yearly pattern. Understanding these Seasons in India is crucial for those preparing for the UPSC Civil service exam, particularly in the Geography section.

The Cold Weather or Winter Season

• Winter Season Duration: Mid-December to Mid-March.
• Sun’s Apparent Path: South of the equator.
• Characteristics:
  • Clear skies.
  • Pleasant weather.
  • Cool and slow north-east trade winds.
  • Low temperature.
  • Low humidity.
  • Wide temperature range.
• Notable Feature: Diurnal temperature range is exceptionally wide, particularly in the country’s interior during winter.

Temperature in Winter Season

• The 20°C isotherm aligns roughly parallel to the Tropic of Cancer.
• South of this isotherm, temperatures remain above 20°C, leading to an absence of clearly defined winter weather.
• In certain regions of Kerala and Tamil Nadu, temperatures frequently soar to 30°C.
• The average temperature in the north stays below 21°C, resulting in distinct winter weather.
• North-west India experiences a mean minimum temperature of about 5°C, while the Gangetic plains register a mean minimum temperature of approximately 10°C.
• The Dras Valley in Kashmir holds the title of India’s coldest location, with the lowest recorded temperature being –45°C in 1908.

Pressure in Winter Season

• Low temperatures, coupled with divergence caused by the STJ (SubTropical Jet Streams) ridge, lead to high air pressure across extensive regions of north-west India.
• South India exhibits lower pressure compared to other parts of the country.
• Winds initiate from a north-westerly high-pressure area and move towards a south-easterly low-pressure area.
• Due to a low pressure gradient, wind velocity remains low.
• The wind’s trajectory is influenced by both the pressure gradient and the physiography.

Western Disturbances in Winter Season

• The arrival of western disturbances often disrupts the prevailing good weather in northwestern and northern India.
• These disturbances intensify notably in Rajasthan, Punjab, and Haryana.
• Progressing eastward through the sub-Himalayan belt, they eventually reach Arunachal Pradesh.
• In the Indus Ganga plains, they result in light rain, while in the Himalayan belt, they bring about snowfall.
• Following the passage of the disturbance, widespread fog and cold waves ensue, causing a decrease in the minimum temperature by 5° to 10°C below normal.
• Fog diminishes visibility, creating significant inconvenience in transportation.

Tropical Cyclones in Winter Season

• Tropical cyclone activity reaches its lowest point during this season.
• Over the course of the season, the frequency of tropical cyclones diminishes.
• This decline is attributed to the combination of low sea surface temperature and the southernmost position of the ITCZ (Intertropical Convergence Zone).
• Storms originating in the Bay of Bengal make landfall in Tamil Nadu, resulting in heavy rain.
• Some of these storms traverse the Arabian Sea from the southern peninsula.
• Arabian Sea experiences fewer storm formations, and those that do form may travel north or west.

Precipitation in Winter Season

• While traversing the Bay of Bengal, the retreating winter monsoons gather moisture, resulting in winter rainfall in Tamil Nadu, south Andhra Pradesh, southeast Karnataka, and southeast Kerala (typically in the first weeks of November).
• The peak seasonal rainfall, approximately 75 cm, takes place between October and December.
• The major concentration is along the southeastern coast of Tamil Nadu and adjoining areas of Andhra Pradesh, gradually diminishing thereafter.
• In northwest India, western disturbances also bring some rainfall.
• Moving from the north and northwest to the east, the rainfall gradually decreases during this period (in contrast to the rainy season).
• In the winter, rainfall occurs in the northeastern part of India.

The Hot Weather Season or Summer Season

• The Summer Season spans from mid-March to May.
• Key features of this season encompass high temperature and low humidity.
• The hot weather season is occasionally denoted as the pre-monsoon period.

The temperature in Summer Season

• The vast range of sun insolation results from the apparent movement of the sun between the equator and the Tropic of Cancer.
• Notably warmer conditions in the southern parts of the country occur in March and April, while higher temperatures in North India manifest in June.
• Southern regions experience peak temperatures (40-45°C) in March.
• In the northern parts of Madhya Pradesh, the highest temperature of around 45°C was recorded in April.
• May marks the hottest month, with temperatures soaring as high as 48°C in Rajasthan.
• Punjab and Haryana witness their highest temperatures in June.
• Historical records include temperatures reaching 50.5°C in Alwar on May 10, 1956, and 50.6°C in Ganganagar on June 14, 1935.
• The highest temperatures occur just before the arrival of the southwest monsoons (late May).
• A substantial diurnal temperature range, with some areas experiencing temperatures as high as 18°C.
• Coastal and southern peninsular regions exhibit comparatively lower maximum summer temperatures due to the cooling effect of the sea.
• Prevailing westerly winds contribute to cooler temperatures on the west coast compared to the east coast.
• Dramatic temperature differences exist between land and sea.
• Heat waves affect the northern and central parts of India during this season.

Heat Waves – A heatwave signifies a duration of remarkably high temperatures in a specific region. – A moderate heatwave is characterized by a temperature surge of 6° to 7°C above normal. – A severe heatwave is identified by a temperature surge of 8°C or more above normal.

• The majority of heatwaves manifest in Rajasthan, Punjab, and Haryana, which are notably distant from the sea. They extend into Uttar Pradesh and Bihar from this region.
• Strong northwesterly winds, a result of intense divergence in north-west India, hinder the progress of sea breeze along the eastern coastal belt. This, combined with a prolonged journey over hot regions, leads to heatwaves in Odisha and Andhra Pradesh.
• Heatwaves typically start by the end of April, reaching their frequency peak in May.
• They persist until the onset of the southwest monsoon.
• The duration of heatwaves is generally four to five days.
• Conversely, heatwaves are infrequent in the peninsular region south of 13°N latitude, attributed to prevailing maritime conditions.

Pressure in Summer Season

• Due to the hot weather, atmospheric pressure experiences a widespread decline throughout the country.
• Strong dynamically induced divergence, however, hinders the initiation of the south-west monsoons over north-west India.

Winds in Summer Season

• The characteristics of winds undergo a dramatic change compared to winter.
• Generally, the wind is light and variable.

Loo

• Loo winds originate from the deserts of Iran, Baloch, and Thar.
• The high temperatures in northwest India generate a significant pressure gradient in May and June.
• Loo winds are hot, dusty, and strong, typically commencing around 9:00 a.m., intensifying gradually, and reaching their peak in the afternoon.
• Blowing at a consistent speed of 30-40 km/h, Loo winds can persist for days.

Andhis

• Andhis are robust dust storms caused by convective phenomena, referred to locally as blinding storms.
• They advance like a solid wall of sand and dust, with wind speeds often ranging between 50 and 60 kilometers per hour, reducing visibility to a few meters.
• Regions prone to andhis include Rajasthan, Haryana, Punjab, Jammu and Kashmir, Delhi, Uttar Pradesh, Bihar, and Madhya Pradesh.
• Although short-lived, the squalls and showers that follow these storms lead to a dramatic, temporary reduction in temperature.

Frontal Thunderstorms in Summer Season

• Thunderstorms occur in the eastern and north-eastern parts of the country, driven by robust convectional movements influenced by the westerly jet stream.
• Typically originating over the Chota Nagpur plateau, they are propelled eastward by westerly winds.
• Regions with the highest frequency of thunderstorms include Assam, Arunachal Pradesh, Nagaland, Mizoram, Manipur, Tripura, Meghalaya, West Bengal, and adjacent areas of Odisha and Jharkhand.

Norwesters and Thunderstorms in Summer Season

• Squalls, known as norwesters, predominantly arise from the northwest in West Bengal and adjoining regions of Jharkhand, Odisha, and Assam.
• These squalls are often intense, with speeds ranging from 60 to 80 km/h.
• Accompanying showers, hailstones can attain the size of a golf ball.
• While causing significant damage to crops, trees, buildings, and livestock, they can be beneficial for the cultivation of tea, jute, and rice.
• In Assam, these storms are termed ‘Barodoli Chheerha.’
• The month of Vaisakh (mid-March to mid-April) sees the highest occurrence of these storms, locally known as Kalabaisakhis, black storms, or a mass of dark clouds of Vaisakha.

Convectional Thunderstorms in Summer Season

• Thunderstorms are observed in Kerala (Mango Showers) and adjoining areas of Karnataka (Blossom Showers) and Tamil Nadu in the south.
• These storms are more prominent during evenings and nights.

Western Disturbances in Summer Season

• As the summer advances, the frequency and intensity of western disturbances diminish.
• In March, April, and May, four, three, and two western disturbances, respectively, traverse northwestern India.
• These disturbances contribute to snowfall in the higher reaches of the Himalayas.

Tropical Cyclones in Summer Season

• The Bay of Bengal and the Arabian Sea serve as the birthplaces for tropical cyclones.
• In March, a few cyclones form in the Bay of Bengal, but they do not impact India’s mainland.
• Cyclone frequency notably increases in April, more than doubling the number from May.
• The Bay of Bengal produces about three-quarters of tropical cyclones, with the Arabian Sea producing the remainder.
• Depressions forming in April are mainly south of 10°N, while those in May originate north of this latitude.
• Most storms initially move west or north-west but later recurve northeast, impacting the Bangladesh and Myanmar’s Arakan Coast.
• Only a few reach the Indian coast; others dissipate at sea.
• In May, tropical storms are anticipated to hit the entire east coast of India, along with the coastal areas of Bangladesh and Myanmar’s Arakan Coast.
• Many are severe, resulting in significant loss of life and property.
• In the Arabian Sea, major storms form between 7° and 12° N latitudes in May, predominantly moving north-westerly away from the Indian coast, with a few heading north-east and eventually making landfall along India’s west coast.

Precipitation in Summer Season

• This season is not entirely without rain, accounting for only one percent of the annual rainfall.
• Dust storms contribute minimal rain to the northeastern regions of the country.
• Snowfall is the predominant form of precipitation in Kashmir, resulting from the influence of western disturbances.
• In Assam, West Bengal, and Odisha, northwestern winds bring rain with high intensity.
• Spring storm showers, induced by northwestern winds, affect these regions.
• In Assam, the limited rainfall is termed “tea showers,” proving highly beneficial for the cultivation of tea, jute, and rice.
• Thunderstorms deliver rain to the coastal areas of Kerala and Karnataka.
• In Tamil Nadu and Andhra Pradesh, these showers are referred to as “mango showers” due to their significant benefits for the mango crop.
• In Karnataka, they are known as “cherry blossoms” because of their impact on coffee plantations.

The Southwest Monsoon or Rainy Season

• The Rainy Season spans from June to September.
• The swift temperature rise over the northwestern plains in May intensifies the low pressure conditions.
• These conditions attract the Southern Hemisphere trade winds from the Indian Ocean by early June.
• The southeast trade winds traverse the equator and enter the Bay of Bengal and the Arabian Sea, becoming entwined in the atmospheric circulation over India.
• Carrying substantial moisture from the equatorial warm currents, these winds then move in a southwesterly direction after crossing the equator.
• The term “Southwest monsoons” is derived from this characteristic.

Southwest Monsoon Bursts

• The onset of rain is abrupt during the southwest monsoon season.
• The initial rain has a significant impact on lowering the temperature.
• The term “break” or “burst” of the monsoons denotes the sudden arrival of moisture-laden winds accompanied by intense thunder and lightning.
• In the coastal areas of Kerala, Karnataka, Goa, and Maharashtra, the monsoon might begin in the first week of June, while in the interior, it may arrive in the first week of July.
• Between mid-June and mid-July, the daytime temperature experiences a drop of 5°C to 8°C.
• The combination of relief and thermal low pressure over northwest India alters the southwesterly direction of these winds approaching the land.
• The approaching monsoon divides into two branches:
  • The Arabian Sea branch
  • The Bay of Bengal branch

The Retreating Monsoon or Cool Season

• Monsoons are recognized for their retreat during the months of October and November.
• Towards the end of September, the southwest monsoon weakens as the low-pressure trough over the Ganga plain begins to shift southward due to the southward movement of the sun.
• By the first week of September, the monsoon withdraws from western Rajasthan.
• By the end of the month, the retreat extends to cover Rajasthan, Gujarat, the Western Ganga plain, and the Central Highlands.

Retreating Monsoon in the Southern Half of India

• By early October, the low-pressure system encompasses the northern parts of the Bay of Bengal, and it shifts over Karnataka and Tamil Nadu by early November.
• The center of low pressure entirely departs from the Peninsula by the middle of December.
• The retreat of the southwest monsoon season is marked by clear skies and increasing temperatures, even though the ground remains damp.
• The ensuing weather turns oppressive due to the combination of high temperature and humidity, commonly known as the ‘October heat.’

Retreating Monsoon in the Northern Half of India

• The temperature undergoes a rapid decline in the latter part of October, particularly in northern India.
• During the retreat of the monsoon in north India, the weather becomes dry, although the eastern part of the Peninsula experiences associated rain.
• The most precipitation occurs in the months of October and November in this region.
• The occurrence of the rainy season is connected to the movement of cyclonic depressions originating in the Andaman Sea, traveling towards the eastern coast of the southern Peninsula.

Effects caused by Retreating Monsoons

• Tropical cyclones pose significant danger, with a predilection for targeting the densely populated deltas of the Godavari, Krishna, and Kaveri rivers.
• Annually, these cyclones wreak havoc in this region.
• The coasts of West Bengal, Bangladesh, and Myanmar have also been impacted by cyclonic storms.
• These depressions and cyclones play a pivotal role in contributing to the majority of the rainfall on the Coromandel coast.
• In the Arabian Sea, such cyclonic storms are less frequent.

Conclusion

A four-season climate presents more living opportunities than a one-season climate. Each of these four seasons provides a unique perspective on life, offering distinct activities and climatic conditions. These variations are also beneficial for sustaining Earth’s features and supporting the diverse life forms, particularly the flora and fauna.

FAQs on Seasons in India

Question: How many seasons are there in India?

Answer: India experiences six seasons, including summer, monsoon, autumn, pre-winter, winter, and spring.

Question: What causes seasons in India?

Answer: The changing seasons in India are primarily caused by the tilt of the Earth’s axis as it orbits the sun, resulting in variations in the intensity and duration of sunlight at different latitudes.

Question: Why is autumn called fall?

Answer: The term “fall” is commonly used in North America to refer to autumn. It originated from the falling of leaves from deciduous trees during this season, marking a distinctive characteristic of autumn in those regions.

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