Indian Climate

Introduction — India's Climate Type

India's climate is best described as Tropical Monsoon — a distinct wet and dry climate driven by the seasonal reversal of winds. Though the northern part lies in the temperate belt (north of the Tropic of Cancer), India is treated as a tropical country due to:

• Himalayas blocking cold Central Asian air masses → winters 3°C–8°C warmer than equivalent latitudes elsewhere.
• Tropical monsoon dominates precipitation patterns nationwide.
• Loo (hot dry westerly wind) in summer pushes north Indian temperatures to levels comparable to the south.
• Agriculture, settlements, diseases, and biodiversity are all tropical in character.

Two defining characteristics:

1. Unity — Most of India receives rainfall in the same season (SW Monsoon, June–September).
2. Diversity — Enormous regional variation in temperature, rainfall, humidity, and wind regime.

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Factors Influencing Indian Climate

1. Latitudinal Location

• Areas south of Tropic of Cancer: Tropical zone — high solar insolation, extreme summers, moderate winters.
• Areas north of Tropic of Cancer: Warm temperate — less insolation but hot summers (due to Loo) and very cold winters (Western Disturbances bring cold waves).
• Coastal regions: Moderate climate irrespective of latitude (maritime effect).

2. Distance from the Sea (Continentality)

• Coastal areas (Mumbai, Chennai, Kochi): Equable/maritime climate — low diurnal and annual temperature range; monsoon arrives first.
• Interior areas (Delhi, Nagpur, Jodhpur): Extreme/continental climate — high temperature ranges; rain arrives late and less.

UPSC Prelims 2005: Correct decreasing order of annual rainfall — Kochi > Kolkata > Patna > Delhi ✓

3. The Himalayas — Climatic Divide

The Himalayas play a dual role:

• Winter: Block cold, dry Siberian/Central Asian air masses from entering India → keeps north India 3°C–8°C warmer than comparable latitudes.
• Monsoon: Act as a physical barrier → force SW Monsoon winds to rise → orographic rainfall on windward (southern) slopes.
• Without the Himalayas: Monsoon winds would pass into Central Asia; most of north India would be a desert.

Why does rainfall decrease west to west across the Indo-Gangetic Plain?

• As the Bay of Bengal branch of the SW Monsoon moves westward, it successively loses moisture after each rainfall episode → progressive decrease in rainfall from Kolkata (~150 cm) → Delhi (~65 cm) → Jodhpur (~30 cm).

4. Physiography / Relief

• Windward slopes (Western Ghats, Meghalaya plateau) → heavy rainfall.
• Leeward/rain shadow areas (Deccan Plateau, Vidarbha, Marathwada) → low rainfall.
• High altitudes → cooler temperatures regardless of latitude.

5. Monsoon Winds

• SW Monsoon (June–September): Primary rainfall source for ~85% of India.
• NE Monsoon (October–December): Brings rainfall to Tamil Nadu and coastal Andhra Pradesh.

6. Upper Air Circulation — Jet Streams

• Subtropical Jet Stream (STJ): Controls monsoon onset/withdrawal (see Ch 9).
• Tropical Easterly Jet (TEJ): Present June–October over Indian plains; linked to active monsoon.
• Polar Front Jet Stream: Influences winter precipitation in northern India.

7. Western Disturbances (WDs)

• Extra-tropical cyclones originating over the Mediterranean, Caspian, and Black Seas.
• Travel eastward embedded in the mid-latitude westerlies; bring winter rain and snow to NW India (Punjab, HP, Uttarakhand, J&K).
• Arrive October–March; responsible for Rabi crop (wheat) rainfall.
• Each WD typically brings 1–5 days of rain/snow to northern India.

2024–2026 Western Disturbance Trends:

• 2024-25 winter: Among warmest in 124 years in India; WDs were weak and fewer than normal.
• Uttarakhand: 47% rainfall deficit (Oct–Dec 2024); HP: 40% deficit — Himalayan snowfall significantly delayed.
• March–April 2025: Unusually intense WDs — six systems active in quick succession since March 13; rare hailstorms across Rajasthan, MP, Punjab; extensive Rabi crop (wheat, mustard) damage.
• March–April 2026: Another spell of "rare" late-season WDs; IMD issued "sweater weather alert" for March 2026 — normally a warm month; 1,000-km linear rain band from Afghanistan through Pakistan into Indian heartland.
• Long-term trend: WD frequency has increased by 60% in April–July over 70 years (off-season WDs) but weakened in winter — reducing snowfall, increasing flood risk.

8. El Niño, La Niña, IOD

(Detailed coverage in Ch 9 — Indian Monsoons)

9. Tropical Cyclones

• Form over Bay of Bengal (more frequent) and Arabian Sea (less frequent, but increasing).
• Affect east coast (especially Andhra Pradesh, Odisha, West Bengal) during October–November.
• 2023: Cyclone Biparjoy (Arabian Sea, June 2023) — strongest pre-monsoon cyclone in Arabian Sea history; made landfall near Jakhau, Gujarat.
• 2024: Cyclone Fengal (Bay of Bengal, November 2024) — made landfall near Puducherry; caused extreme rainfall (~50 cm in 24 hours) in Puducherry.

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Seasons of India (IMD Classification)

India has four distinct seasons:

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Season 1 — Cold Weather Season (December–February)

• Sun's apparent position: over Tropic of Capricorn → short days, oblique rays → low temperatures.
• Temperature gradient: Decreases from south to north.
  • Kashmir/Ladakh: −30°C to −40°C in extreme areas.
  • Coastal Tamil Nadu/Kerala: 20°C–25°C.
• Pressure gradient: High pressure over NW India, low pressure over Bay of Bengal → NE Trade Winds blow → dry weather for most of India.
• Western Disturbances: Bring rains to Punjab, HP, J&K, Uttarakhand → crucial for Rabi crops (wheat, mustard, barley).
• Cold waves: Originate from Siberian highs; Punjab, Haryana, UP, Rajasthan affected; Loo does not blow; instead, cold northwesterly winds.
• Local phenomena: Fog in Indo-Gangetic plains (dense winter fog disrupts aviation, rail, road).

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Season 2 — Hot Weather Season (March–May)

• Sun moves toward Tropic of Cancer → intense heating of the landmass.
• Temperatures: North and central India experience extreme heat; Rajasthan may exceed 50°C.
• Low-pressure system develops over the Thar Desert and NW India → draws moisture from the oceans.

Local Winds and Pre-Monsoon Phenomena:

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Season 3 — SW Monsoon Season (June–September)

(Detailed in Ch 9 — Indian Monsoons)

• Peak rainfall for most of India (85%+ of annual rainfall).
• Onset: ~June 1 (Kerala); covers entire India by mid-July.
• Withdrawal: September 1 (NW India); complete by November.
• Active and break spells of monsoon alternate throughout the season.

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Season 4 — Retreating Monsoon / NE Monsoon (October–November)

• SW Monsoon withdraws northwestward from the Indian peninsula.
• Low pressure shifts to Bay of Bengal → cyclogenesis zone.
• Tamil Nadu receives 48–50% of its annual rainfall from the NE Monsoon.
• October heat: After monsoon withdrawal, clear skies + high humidity → oppressive heat ("October Heat").
• Cyclone season: October–November is peak season for Bay of Bengal cyclones affecting Andhra Pradesh, Odisha, West Bengal, Tamil Nadu.

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Climatic Regions of India (Köppen Classification)

Köppen divided India into several climatic types using temperature and precipitation data:

Stamp's Classification (Simplified):

1. Hot Desert Climate — Thar Desert
2. Semi-Arid Steppe — Rajasthan margins
3. Tropical Savanna — peninsular India
4. Tropical Monsoon — coastal western India
5. Humid Subtropical — northern plains
6. Mountain Climate — Himalayas

UPSC Prelims 2002: Station with 26°C annual temperature, 63 cm rainfall, 9°C annual range → Chennai (Tropical Savanna) ✓

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Temperature Patterns

Temperature Extremes

Temperature Ranges

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Rainfall Distribution

Annual Rainfall Map (Zones)

Wettest station: Mawsynram, Meghalaya (~11,871 mm average annual rainfall) — world's wettest place. Driest station (mainland): Jaisalmer, Rajasthan (~100 mm annual).

Rainfall Variability

• High variability (>40% coefficient of variation): Arid and semi-arid regions of Rajasthan — uncertain, unreliable rainfall year to year.
• Low variability (<20%): Humid regions — Western Ghats, NE India — reliable, consistent.
• Flood-prone: Brahmaputra basin (Assam), Bihar (Kosi), Odisha (Mahanadi).
• Drought-prone: Vidarbha, Marathwada, Telangana, Rayalaseema, Bundelkhand, parts of Rajasthan.

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Local Winds Summary

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Tropical Cyclones — India's Vulnerability

Formation Zones

• Bay of Bengal: ~5–6 cyclones/year on average; more intense due to warmer SST and lower wind shear.
• Arabian Sea: ~1–2/year; historically less frequent but intensifying due to climate change.

Cyclone Seasons

• Pre-monsoon (April–June): Arabian Sea cyclones; rare but intensifying (Biparjoy 2023).
• Post-monsoon (October–December): Main Bay of Bengal cyclone season; affects east coast.

Scale and Classification (IMD)

Recent Major Cyclones (2020–2026)

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Climate Change and India — Updated 2026

Temperature Rise

• India's mean annual temperature has risen ~0.15°C per decade (1951–2016) — IMD data.
• 2024: India's hottest year on record since 1901 — confirmed by IMD (January 15, 2025). Annual average land surface temperature was +0.65°C above LPA (1991-2020 base), surpassing the previous record of +0.54°C in 2016.
• 2025: India's 8th warmest year since 1901 (+0.28°C above 1991-2020 LPA). Warmest winter in 124 years (Jan–Feb: +1.17°C); February 2025 = hottest February on record (+1.36°C). First-ever heatwave in February (Goa/Maharashtra, Feb 25, 2025). Extreme weather recorded on 331 of 334 days in 2025 — deadliest year in recent climate history (2,760 deaths; 9.47 million ha crops affected).
• Temperature increase is faster in minimum temperatures (nights warming faster than days).

Heatwaves

• 2024 Heatwave (third consecutive severe year):
  • 536 heatwave days — highest since 2010 (578 days).
  • Churu, Rajasthan: 50.5°C (highest in 8 years).
  • Delhi: Minimum temperature of 35.2°C (hottest night ever recorded).
  • 219 official deaths (June 3, 2024); independent estimate: 733 deaths, 40,000+ heatstroke cases.
• 2025: Heatwave alerts issued in NW India as early as March 25.

Changing Rainfall Patterns

• Increase in extreme rainfall events — floods in traditionally drier areas.
• Decrease in number of rainy days — more intense, concentrated rainfall.
• Drought and flood occurring simultaneously in different parts of India in the same year.
• 2025: Rising night-time temperatures and extreme rainfall across all seasons.

Western Disturbances (Climate Change Impact)

• Off-season WDs (April–July) have increased 60% in frequency over 70 years → unseasonal hailstorms, floods.
• Winter WDs weakening → reduced Himalayan snowfall → long-term impact on Himalayan glaciers and perennial river flow.

Cyclone Intensification

• Arabian Sea cyclones intensifying due to warming Indian Ocean SSTs.
• Post-cyclone intensification (rapidly intensifying cyclones) more common since 2020.

UPSC Mains Angle: "India is experiencing climate change through both extremes — intense heat and extreme rainfall. Examine with data from 2020–2026."

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UPSC Corner

Key One-Liners for Prelims

• India's climate type = Tropical Monsoon (monsoon — most precise)
• Loo = hot, dry, westerly wind; summer; NW India; causes heat strokes
• Kalbaisakhi = violent NW thunderstorms; West Bengal/Assam; pre-monsoon; beneficial for jute
• Mango Showers = pre-monsoon; Kerala/Karnataka; ripens mangoes
• Wettest place: Mawsynram (~11,871 mm) | Driest (mainland): Jaisalmer (~100 mm)
• Highest diurnal range: Thar Desert | Lowest: Coastal regions
• Highest annual range: Himalayan/NW India | Lowest: Coastal/southern India
• Western Disturbances = Mediterranean origin; winter rain/snow to NW India; Rabi crop lifeline
• India: 0.15°C/decade temperature rise (1951–2016)
• 2024: Hottest year on record globally; India — 536 heatwave days; Churu 50.5°C; Delhi hottest night (35.2°C)
• Biparjoy (2023) = strongest pre-monsoon Arabian Sea cyclone on record
• Fengal (2024) = BoB cyclone; 50 cm rain/24 hrs; Puducherry landfall
• India's warmest winter in 124 years = 2024-25

Mains GS1 Questions

1. "Discuss the factors that influence the climate of India. How do the Himalayas act as a climatic divide?"
2. "Explain the concept of continentality. How does India's coastline mitigate extreme climate?"
3. "What are Western Disturbances? How are climate change-driven changes in WDs affecting India's water security?"
4. "India is witnessing increasing frequency and intensity of extreme weather events. Examine with evidence from 2020-2026."
5. "Differentiate between Kalbaisakhi and Loo. In what ways are local winds important for India's economy?"

MCQ Trap Awareness

• Trap: "Loo is a cold wind" → Wrong — Loo is a hot, dry wind.
• Trap: "Kalbaisakhi blows in Rajasthan" → Wrong — it's specific to West Bengal and Assam.
• Trap: "Western Disturbances originate in the Bay of Bengal" → Wrong — they originate over the Mediterranean/Caspian/Black Seas.
• Trap: "Mawsynram and Cherrapunji are in Assam" → Wrong — both are in Meghalaya.
• Trap: "India has 5 seasons" → Per IMD, India officially has 4 seasons.
• Trap: "Arabian Sea cyclones are more frequent than Bay of Bengal cyclones" → Wrong — BoB is far more cyclone-prone (~5× more frequent).
• Trap: "2024 was India's hottest year only globally" → It was the hottest year both globally and in India on record.