Climate and Monsoon
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Climate and Monsoon — Key Facts for KPSC KAS • Monsoon: Derived from Arabic word “Mausam” (season). Indian monsoon is a seasonal reversal of wind direction driven by differential heating of land and sea. • Mechanism: During summer (June-September), the Indian subcontinent heats up creating a low-pressure area over northwestern India. The southeast trade winds from the Southern Hemisphere cross the equator and are deflected as southwest monsoons by the Coriolis force. • ITCZ: Inter-Tropical Convergence Zone shifts northward during summer, establishing the monsoon trough. • Four seasons: Winter (Jan-Feb), Summer/Pre-Monsoon (Mar-May), Southwest Monsoon (Jun-Sep), Post-Monsoon/Retreating Monsoon (Oct-Nov). • Rainfall variability: Western Rajasthan: <100 mm; Cherrapunji (Meghalaya): 11,000+ mm (world’s highest); Mawsynram: 11,872 mm — highest recorded. • El Niño connection: El Niño events correlate with weaker monsoon years (1999, 2009, 2015 were deficit years).
⚡ Exam tip: KPSC KAS frequently asks about the monsoon mechanism, rainfall distribution across India, and climate classification. Karnataka-specific questions often involve ** Karnataka’s rainfall patterns** and agricultural vulnerability to monsoon failure.
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Climate and Monsoon — KPSC KAS Study Guide
Monsoon System of India
Mechanism of the Indian Monsoon
The Indian monsoon is a complex, multi-causal weather phenomenon not fully explained by any single factor. Its annual rhythm shapes India’s agricultural calendar, water resources, and economic cycles.
Step 1 — Differential Heating (April-May):
- The Indian subcontinent heats rapidly in April-May while the Indian Ocean remains relatively cooler
- This creates a thermal contrast between land and sea
- Maximum temperatures reach 45°C+ in Rajasthan, Punjab, and Gujarat
Step 2 — Formation of Low Pressure (June):
- A heat low develops over northwestern India (Rajasthan-Punjab region)
- The Tibetan Plateau (at 3,000-5,000m elevation) warms intensely, creating upper-level atmospheric pressure
- This upper-level warming strengthens the monsoon circulation
Step 3 — Onset of the Monsoon (June):
- The southeast trade winds from the Southern Hemisphere cross the equator near the Somali coast (Findlater Jet or Somali Jet)
- Deflected by the Coriolis force and the Indian subcontinent’s geometry
- Enter the Indian subcontinent as southwest monsoon winds
- The Inter-Tropical Convergence Zone (ITCZ) migrates to its northernmost position (around 25-30°N)
Step 4 — Monsoon Advance:
- The monsoon enters through two branches:
- Arabian Sea Branch: Hits the Western Ghats, moves inland; produces orographic rainfall
- Bay of Bengal Branch: Crosses Bengal and strikes the Northeast; moves up the Ganga plain
- By early July, both branches cover most of India
Branches and Rainfall Distribution
Arabian Sea Branch:
- Strikes Western Ghats → Heavy rainfall on windward slopes (Maharashtra coast, Goa, Karnataka coast, Kerala)
- Leeward side (rain shadow): Karnataka interior, Maharashtra hinterland receive less than 100 cm
- Crosses central India, but depleted of moisture
Bay of Bengal Branch:
- Picks up moisture from Bay of Bengal
- Enters through Assam, West Bengal, Odisha
- Strikes Eastern Himalayas — Cherrapunji and Mawsynram receive the world’s highest rainfall
- Moves up the Ganga valley
Regions of High Rainfall:
- Western slopes of Western Ghats: 200-300 cm
- Northeast India (Meghalaya, Assam): 200-1,000+ cm
- Sub-Himalayan Bengal and Sikkim: 200-300 cm
- Andaman and Nicobar Islands: 150-300 cm
Regions of Low Rainfall (Desert and Rain Shadow):
- Western Rajasthan: <25 cm
- Interior Karnataka (rain shadow of Western Ghats): 50-75 cm
- Gujarat (except Saurashtra): 50-75 cm
- Punjab plain: 50-75 cm
- Leh and Ladakh: <10 cm
Seasons in India
Winter (January-February):
- Temperature: 10-15°C average in north; 20-25°C in south
- Western disturbances: Extra-tropical cyclonic storms from Mediterranean (carry moisture); bring rain and snow to Punjab, Haryana, Delhi
- Snowfall: Himalayas receive heavy snowfall; serves as natural reservoir
Summer/Pre-Monsoon (March-May):
- Temperature: Very hot; 40-45°C in Rajasthan, Punjab, Gujarat; coastal areas slightly cooler
- Dust storms: Frequent in Rajasthan, Punjab, Haryana (called “andhi”)
- Thunderstorms: Nor’westers (called “Kal Baisakhi” in West Bengal) — pre-monsoon convectional storms
- Heat waves: Deadly; 2015 heat wave killed 2,000+ people across India
Southwest Monsoon (June-September):
- 75-90% of India’s annual rainfall concentrated in these four months
- Break in monsoon (monsoon trough shifts) causes rainfall gaps
- Break monsoon: When the monsoon trough shifts to foothills of Himalayas, central India receives less rainfall
Retreating Monsoon (October-November):
- Monsoon retreats from north to south
- Cyclones: Bay of Bengal produces severe cyclones (1999 Odisha supercyclone — 10,000+ deaths); cyclone season peaks in November
- ** Northeast monsoon (October-December): Tamil Nadu receives rain from retreating monsoon (also called post-monsoon monsoon or ** northeast monsoon)
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Climate and Monsoon — Comprehensive KPSC KAS Notes
Advanced Monsoon Dynamics and Climate Classification
Traditional and Modern Monsoon Theories
Classical Theory (Sir John Eliot, 1890s):
- Monsoon = modified trade winds
- Summer: land heated → low pressure → winds blow from sea to land
- Winter: land cooled → high pressure → winds blow from land to sea
Thermal Theory (Flohn, 1950s):
- Tibetan Plateau as the key driver — its large-scale heating during summer creates strong upper-level anticyclone
- This heating drives the monsoon circulation at upper levels
- Explains why the monsoon starts in the Bay of Bengal before the Arabian Sea
Modern Understanding: The monsoon is now understood as a tropical atmospheric circulation system involving:
- Ocean-atmosphere interaction: Sea surface temperatures (SST) of Indian Ocean
- Walker Circulation: East-west circulation pattern in the tropical Pacific affects Indian monsoon
- ENSO (El Niño-Southern Oscillation): El Niño (warm SST in eastern Pacific) generally weakens monsoon; La Niña strengthens it
- Indian Ocean Dipole (IOD): Positive IOD (cool western Indian Ocean, warm eastern) strengthens monsoon
El Niño and the Indian Monsoon
El Niño (warming of central/eastern Pacific SST) is the most studied monsoon influence:
| El Niño Year | Monsoon Performance |
|---|---|
| 1997-98 | Strong positive IOD; monsoon actually above normal |
| 1999 | Deficit monsoon |
| 2002 | Deficit monsoon |
| 2009 | Deficit monsoon (22% below normal in some regions) |
| 2015 | Deficit monsoon |
| 2019 | Near normal (despite El Niño conditions) |
Key point: El Niño explains approximately 25-30% of monsoon variance — other factors (IOD, local SST, Tibetan snow cover) play significant roles.
Regional Climate Classifications
India’s diverse topography produces multiple climate zones:
Köppen Classification:
| Climate Type | Characteristics | Regions |
|---|---|---|
| Aw (Tropical Wet-and-Dry) | Distinct dry winter; wet summer | Central India, Odisha, Karnataka plateau |
| Am (Tropical Monsoon) | Short dry season; heavy monsoon | Kerala, Goa, Western Ghats |
| As/Aw (Tropical Savanna) | Very dry winter | Tamil Nadu interior |
| BShw (Semi-Arid Steppe) | Evaporation exceeds precipitation | Karnataka plateau interior, Maharashtra |
| BWhw (Hot Desert) | Very low rainfall | Western Rajasthan, Gujarat |
| Cwg (Humid Subtropical) | Dry winter; hot summer | Northern plains, UP, Bihar |
| E (Mountain) | Above freezing only in summer | Himalayas above 3,000m |
Karnataka’s Climate
Karnataka illustrates India’s climatic diversity:
Three distinct zones:
- Coastal Karnataka (Malenadu): Tropical monsoon climate; 2,000-3,000 mm rainfall; thick forests
- Karnataka Plateau (Mysore region): Tropical savanna; 500-700 mm rainfall; deciduous forests; semi-arid in north
- Northern Karnataka (Hyderabad-Karnataka): Semi-arid; <500 mm rainfall; vulnerable to drought
Southwest Monsoon failure impacts Karnataka:
- 2012: Severe drought in north Karnataka; tank irrigation systems (Karnataka’s traditional system) failed
- Kabini River depletion affecting water supply to Mysore and Bangalore
- Cauvery inflow reduction affecting Karnataka’s water share from the river
Climate Change and the Monsoon
Observed changes:
- Increasing variability: Monsoon breaks and extreme rainfall events becoming more frequent
- Intensifying extremes: 2019, 2020, 2021 saw record-breaking rainfall events causing floods
- Decreasing rainy days: Total number of monsoon days decreasing but intensity per day increasing
- Late onset: Monsoon arrival in Kerala (first point of entry) has been delayed in some years
Projections:
- IMD projections: India may see 2-4°C temperature increase by 2070
- Monsoon rainfall likely to become more concentrated (fewer rain days, higher intensity when it rains)
- Sea level rise threatening coastal Karnataka (Mangalore, Udupi), Kerala, Odisha, Gujarat
- Glacial melt in Himalayas: Gangotri glaciers retreating; temporary increase in river flows followed by long-term decline
Heat Waves in India
India experiences severe heat waves, particularly in May-June:
Definition (IMD):
- Heat wave: Departure from normal maximum temperature by 4.5-6.4°C
- Severe heat wave: Departure of 6.5°C or more
- When actual max temperature is 45°C or above, criteria adjusted
Notable events:
- 2003 Andhra Pradesh heat wave: 1,500+ deaths
- 2015 India-Pakistan heat wave: 3,000+ deaths; 48°C in Delhi; 54°C in Phalodi (Rajasthan) — world’s highest recorded temperature
Vulnerable regions: Rajasthan, Gujarat, Punjab, Haryana, Uttar Pradesh, Andhra Pradesh, Telangana, Odisha, West Bengal
Mitigation measures:
- Heat Action Plans: First implemented in Ahmedabad (2013); now in 23 states
- National Disaster Management Authority (NDMA) guidelines: Early warning systems, public awareness, urban heat mitigation
Examination Strategy
KPSC KAS commonly asks:
- Explain the mechanism of the Indian monsoon with reference to differential heating
- Distinguish between the Arabian Sea branch and Bay of Bengal branch of the monsoon
- Discuss the impact of El Niño on the Indian monsoon
- Classify India’s climate regions using the Köppen system
- Explain Karnataka’s regional climate variations
Key distinctions:
- Southwest monsoon (June-September) vs Northeast monsoon (October-December)
- Orographic rainfall (Western Ghats) vs convectional rainfall (Chota Nagpur plateau)
- Break monsoon vs active monsoon
- El Niño vs La Niña vs Positive Indian Ocean Dipole
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