BharatNotes Why this chapter matters for UPSC: The monsoon is arguably the most important single topic in Indian geography for UPSC. Questions appear in both Prelims (mechanism, onset, retreating monsoon, local wind names) and Mains (monsoon and agriculture, water security, climate change). Climate regions and rainfall distribution underpin questions on agriculture, drought, floods, and environmental policy.
PART 1 — Quick Reference Tables
| Monsoon Season | Months | Key Features |
|---|---|---|
| Hot/Pre-monsoon | March–May | Loo winds; Kal Baisakhi; Mango showers; temperatures 40–48°C |
| Southwest Monsoon | June–September | Onset Kerala ~June 1; orographic rainfall; Mawsynram 11,871 mm/year |
| Retreating Monsoon | October–December | NE monsoon; Tamil Nadu peak rainfall; Bay of Bengal cyclones |
| Winter/Cool Season | December–February | Western Disturbances; snowfall N India; rabi crops |
| Climate Station | Annual Rainfall | Season of Maximum Rain |
|---|---|---|
| Mawsynram (Meghalaya) | ~11,871 mm | June–September (SW Monsoon) |
| Cherrapunji (Meghalaya) | ~11,430 mm (historic record holder) | June–September (SW Monsoon) |
| Mumbai | ~2,400 mm | June–September |
| Chennai | ~1,200 mm | October–December (NE Monsoon) |
| Jaisalmer (Rajasthan) | ~100 mm | Negligible; semi-arid |
| Leh (Ladakh) | ~100 mm | Very low; cold desert |
| Delhi | ~714 mm | July–August |
| Controlling Factor | Effect on India's Climate |
|---|---|
| Latitude | Tropic of Cancer divides — south tropical, north subtropical |
| Altitude | Temperature decreases ~6.5°C per 1,000 m rise; hill stations cooler |
| Distance from sea | Coastal areas more moderate; interior more extreme (continental) |
| Monsoon winds | Dominant factor; SW monsoon brings ~75% of India's annual rainfall |
| Relief (orography) | W Ghats → heavy windward rain, rain shadow to leeward (Deccan) |
| Western Disturbances | Winter rain/snow to North India; critical for rabi crops |
PART 2 — Detailed Notes
India's Diversity of Climates
Despite being predominantly a tropical monsoon country, India contains within its borders an extraordinary range of climate types:
- Tropical rainforest — NE India (Meghalaya, Assam), Western Ghats, Andaman & Nicobar Islands
- Hot desert — Thar Desert (Rajasthan, western Gujarat)
- Cold desert — Ladakh (high altitude, low precipitation, extreme cold)
- Alpine — High Himalayas
- Humid subtropical — Northern plains (hot summers, cool winters, moderate rain)
- Tropical wet and dry (savanna) — Deccan Plateau, central India
This diversity is shaped by six major controlling factors.
Factors Controlling India's Climate
Orographic Rainfall: Rainfall caused when moist air is forced to rise over a mountain barrier. As air rises, it cools, condenses, and precipitates on the windward (facing wind) side. The leeward side receives little rain — called the rain shadow zone. The Western Ghats create one of the world's most dramatic orographic rainfall gradients: Mahabaleshwar (windward) receives ~6,000 mm/year; Pune (leeward, ~160 km east) receives ~700 mm/year.
Western Disturbances: Extra-tropical cyclones originating over the Mediterranean Sea and Caspian Sea that travel eastward along the jet stream and bring winter rainfall and snowfall to northwest India (Punjab, Haryana, Himachal, J&K, Uttarakhand). They are critical for rabi crops (wheat, mustard, barley). A weak Western Disturbance season means drought for wheat farmers in Punjab and Haryana.
The Four Seasons of India
Season 1 — Hot/Pre-monsoon Season (March–May)
Temperature rises rapidly after February. By May, northwest India (Rajasthan, Punjab) records temperatures of 40–48°C. Key weather phenomena:
- Loo: A hot, dry, dust-laden wind blowing from the west and northwest over the Indo-Gangetic Plains during May–June; temperatures can exceed 48°C; can be fatal to humans and livestock.
- Kal Baisakhi (Norwesters): Violent pre-monsoon thunderstorms over West Bengal and Assam; occur in the evening; can cause significant damage but also bring relief from heat; important for the tea crop (Assam).
- Mango Showers: Pre-monsoon showers over Kerala and Karnataka; critical for mango development and the coffee crop (Karnataka).
- Cherry Blossom Showers / Coffee Blossoms: Pre-monsoon showers in Assam and the Western Ghats that trigger the tea and coffee flowering.
Season 2 — Southwest Monsoon (June–September)
Southwest Monsoon: The dominant rainfall system of India, bringing approximately 75% of the country's annual precipitation. Driven by the differential heating between the Indian landmass (rapidly heating in summer → strong low pressure) and the Indian Ocean (cooler → high pressure). Moisture-laden winds rush from the ocean toward the low pressure over the land, bringing widespread rainfall.
The SW Monsoon arrives in two branches:
- Arabian Sea Branch: Strikes the Western Ghats in early June (onset at Kerala typically around June 1, ±1 week); gives heavy orographic rainfall to Kerala, Goa, Maharashtra, Karnataka (windward side); continues north to Mumbai, Gujarat; crosses to MP and Rajasthan (rain shadow of Aravallis).
- Bay of Bengal Branch: Enters India through NE India (Assam, Meghalaya) first; gives the heaviest rainfall in the world to Mawsynram and Cherrapunji (Meghalaya); then bends westward along the Gangetic plains; both branches merge over north India.
UPSC GS1 — Monsoon Onset and "Burst": The sudden onset of the southwest monsoon over Kerala is marked by heavy rainfall, strong winds, and overcast skies — this is called the "burst" of the monsoon. The exact onset date is carefully tracked by IMD. Advance of monsoon northward follows a standard "isochrone" (lines of equal date of monsoon arrival). The monsoon reaches Delhi typically around June 27–July 1 and covers all of India by mid-July.
Monsoon Withdrawal: The retreat of the SW monsoon starts from northwest Rajasthan in mid-September and is complete by mid-October from mainland India. The Bay of Bengal branch lingers longest, transitioning into the NE monsoon.
Mawsynram and Cherrapunji: Both located in the Khasi Hills of Meghalaya; the southern slopes face the Bay of Bengal branch of the monsoon; the funnel-shaped terrain amplifies orographic uplift. Mawsynram (~11,871 mm/year average) is currently recognised as the world's wettest inhabited place by average annual rainfall. Cherrapunji holds records for highest rainfall in a calendar month (9,300 mm, July 1861) and a calendar year (26,461 mm, 1860–61).
Season 3 — Retreating Monsoon / Post-monsoon (October–December)
As the SW monsoon withdraws, the Northeast Monsoon picks up moisture over the Bay of Bengal and brings rainfall to:
- Tamil Nadu (coast and interior) — November–December peak
- Andhra Pradesh (southern coast)
- Parts of Kerala and Karnataka
Chennai receives ~60% of its annual rainfall during this NE monsoon period (October–December). Cuddalore and Nagapattinam districts are the wettest during this period. This is also the peak season for Bay of Bengal cyclones (October–December).
Season 4 — Winter/Cool Season (December–February)
Western Disturbances and Rabi Agriculture: Western Disturbances typically affect north India 4–7 times between November and March. Each brings 1–3 days of cloud cover, light to moderate rainfall on the plains, and snowfall in the hills. This moisture is essential for wheat cultivation across the Punjab-Haryana breadbasket. India's wheat production (~110 million tonnes/year) depends on these winter rains. A poor WD season reduces wheat yield significantly, with implications for food security and inflation.
Temperatures drop sharply, especially in north India. Hills receive snowfall. The rest of India (except TN) is dry. Fog is a significant hazard in the Indo-Gangetic Plain during December–January, disrupting road, rail, and air transport.
Climate Regions of India (Köpppen Classification)
India's climate regions based on the modified Köpppen system:
- Aw (Tropical Wet and Dry): Most of peninsular India; distinct dry season; most common climate type
- Am (Tropical Monsoon): Western coast, parts of NE India; very high rainfall
- Af (Tropical Rainforest): Extreme NE India, W Ghats pockets; no dry season
- BWh (Hot Desert): Western Rajasthan, Thar Desert
- BSh (Hot Semi-arid): Parts of Deccan plateau, Saurashtra, Kutch
- Cwa (Humid Subtropical): Northern plains, foothills of Himalayas; hot summers, mild winters
- ET (Tundra/Alpine): High Himalayas
- BW (Cold Desert): Ladakh
Climate Change Impacts on India's Climate
UPSC GS3 — India's Climate Commitments and Vulnerabilities: India is one of the world's most climate-vulnerable countries while also being the 3rd largest emitter of greenhouse gases (after China and USA).
India's Nationally Determined Contributions (NDCs):
- NDC 2.0 (2022, covers up to 2030): Achieve net zero by 2070; 500 GW renewable by 2030; 50% non-fossil installed capacity by 2030 (already achieved: 52.57% as of Feb 2026); reduce emission intensity by 45% from 2005 levels by 2030; carbon sink of 2.5–3 billion tonnes
- NDC 3.0 (Cabinet approved 25 March 2026, covers 2031–2035): 47% emissions intensity reduction from 2005 levels by 2035; 60% non-fossil installed capacity by 2035; carbon sink of 3.5–4 billion tonnes COâ‚‚-equivalent
Observed climate change impacts on India's climate:
- Monsoon becoming more erratic — more "intense rain days" but fewer overall rain days
- Extreme rainfall events increasing (Kerala floods 2018, Uttarakhand 2021, Delhi flooding 2023)
- Arabian Sea cyclones intensifying in duration and peak intensity
- Glacial Lake Outburst Floods (GLOFs) increasing in Himalayas
- Heatwave days increasing across India — 2024 recorded severe heatwaves in April-June affecting 40+ crore people
[Additional] 3a. Southwest Monsoon 2024 — 108% of LPA, Above-Normal Season
The chapter covers India's monsoon climate and its characteristics but has no data on the most recent monsoon season. Southwest Monsoon 2024 was an above-normal season: cumulative rainfall was 934.8 mm, which equals 108% of the Long Period Average (LPA) of 868.6 mm (1971-2020 baseline). This is directly testable in UPSC Prelims and GS1 — the monsoon's geographic distribution, its measurement, and its deviation from the LPA are core concepts.
Key Terms — Monsoon Measurement:
| Term | Meaning |
|---|---|
| LPA (Long Period Average) | The average rainfall over the entire Indian monsoon season (June–September) computed over 50 years; current LPA = 868.6 mm (1971–2020 baseline, revised periodically) |
| % of LPA | How this year's rainfall compares to the LPA; IMD classifies: <90% = Deficient; 90–95% = Below Normal; 96–104% = Normal; 105–110% = Above Normal; >110% = Excess |
| IMD seasonal categories | The five IMD bands used to classify annual monsoon performance — key for Prelims MCQs |
| JJAS | June-July-August-September — the four months of the Southwest Monsoon season; the rainfall measured to compute % of LPA |
| Withdrawal | When the monsoon retreats northward from Rajasthan in September–October; in 2024, withdrawal from northwest India began September 23 (5 days late) |
| Meteorological subdivision | IMD divides India into 36 meteorological subdivisions for regional rainfall analysis — e.g., "Central India," "South Peninsula," "East & Northeast" |
[Additional] Southwest Monsoon 2024 — Performance Data (GS1 — Indian Climate / GS3 — Agriculture):
Overall 2024 monsoon (June–September):
- Total cumulative rainfall: 934.8 mm
- LPA (1971–2020 baseline): 868.6 mm
- % of LPA: 108% → classified as Above Normal
- Last above-normal year: 2020 (109% LPA)
Month-wise performance:
| Month | % of LPA | Classification |
|---|---|---|
| June 2024 | 111% | Excess |
| July 2024 | 109% | Above Normal |
| August 2024 | 116% | Excess |
| September 2024 | 111% | Excess |
| Full season (JJAS) | 108% | Above Normal |
Regional performance:
| Region | % of LPA | Classification |
|---|---|---|
| Central India | 119% | Excess |
| South Peninsula | 114% | Excess |
| Northwest India | 107% | Above Normal |
| East & Northeast India | Deficit | Below Normal |
District-level distribution:
- 78% of India's districts recorded normal, excess, or large excess rainfall
- Only 22% of districts recorded deficient or scanty rainfall (mostly East & Northeast)
Monsoon withdrawal 2024:
- Southwest Monsoon withdrawal from northwest India began September 23, 2024 — approximately 5 days late compared to the normal date of September 17
Agricultural and water significance:
- Above-normal monsoon 2024 contributed to good Kharif crop production and improved reservoir levels
- As of October 1, 2024: 150 major reservoirs at 89% of total live storage capacity (CWC data) — well above 10-year average of 75%
UPSC synthesis: SW Monsoon 2024 = GS1 climate + GS3 agriculture. Key exam facts: 934.8 mm = 108% LPA (LPA = 868.6 mm, 1971-2020 baseline); classified Above Normal; month-wise: June 111%, July 109%, August 116%, September 111%; Central India 119% Excess; East & Northeast = deficit; 78% districts normal/excess; withdrawal September 23 (5 days late, normal = September 17); 150 major reservoirs at 89% capacity October 2024. IMD classification thresholds: <90% Deficient, 90-95% Below Normal, 96-104% Normal, 105-110% Above Normal, >110% Excess — these bands are high-frequency Prelims trap questions.
[Additional] 3b. Heatwave 2024 — Economic Losses and Labour Impact
The chapter covers temperature extremes and heatwaves as part of India's climate, but with no data on economic consequences. India's heatwave season of 2024 (March–June) caused 247 billion labour hours lost and $194 billion in economic losses — the largest recorded heat-related economic damage for India. This is a GS3 angle (economic cost of climate change, labour productivity) distinct from the GS1/disaster management angle of heatwave deaths and temperatures.
Key Terms — Heatwave Economics:
| Term | Meaning |
|---|---|
| Heat Action Plan (HAP) | A district/city-level plan prepared by NDMA or DDMA specifying trigger thresholds, cooling centre activation, advisory circulation, and ASHA worker protocols for heatwave response |
| NDMA | National Disaster Management Authority — apex body under Disaster Management Act 2005; chaired by Prime Minister; prepares national guidelines for all disasters including heatwaves |
| DDMA | District Disaster Management Authority — implements heat action plans at district level; headed by District Collector |
| Wet Bulb Temperature | A measure combining temperature AND humidity — the critical threshold for human heat tolerance is wet bulb temperature of 35°C (equivalent to ~46-47°C dry bulb at high humidity); beyond this, the human body cannot cool itself |
| Heat stress | Physiological condition where the body cannot maintain normal temperature — leads to heat exhaustion, heatstroke, organ failure; disproportionately affects outdoor workers, elderly, and children |
| WRI | World Resources Institute — global environmental research organisation; published India heatwave labour impact data for 2024 |
[Additional] India Heatwave 2024 — Economic and Labour Impact (GS3 — Climate Change / GS2 — Social Justice / GS1 — Climate):
Scale of heatwave 2024 (March–June 2024):
- Labour hours lost: 247 billion hours — due to workers stopping work or reducing pace during peak heat hours (mostly 11am–4pm)
- Economic losses: Estimated $194 billion (approximately Rs.16 lakh crore) in productivity losses
- Heatstroke cases reported: 44,000+ across India (2024 season)
- Workers exposed: ~75% of India's workforce — approximately 380 million workers — are engaged in heat-intensive outdoor labour (agriculture, construction, street vending, waste collection)
Who bears the burden:
- Delhi informal sector workers: net earnings fell approximately 40% during peak heatwave days (workers rest during hottest hours; daily wage workers lose income directly)
- Agricultural labourers: productivity drop of 15–20% for every 1°C above 27°C threshold (ILO data)
- Construction sector: accounts for largest share of heat-related labour loss (outdoor, no shade, physically demanding)
Future risk:
- 4.5% of India's GDP at risk from heat stress by 2030 (Climate Impact Lab projections)
- India's average temperatures have already increased by 0.7°C since 1900 (IMD); southern and central India most affected
Government preparedness (2024):
- NDMA: Began planning for 2024 heatwave season as early as October 2023 — unusually early start reflecting lessons from 2022 and 2023 pre-monsoon heat
- NDMA national workshop on heatwave preparedness held February 2024
- DDMA Delhi: Released Delhi Heat Action Plan 2024-25 in April 2024 — before the peak season began; included:
- Activation of 800+ cooling centres across Delhi
- Colour-coded heat alerts (Yellow/Orange/Red) linked to automatic protocols
- ASHA workers conducting daily door-to-door wellness checks in vulnerable wards during Red alerts
- Construction sites required to provide ORS, shade, and rest breaks
IMD heatwave definition (for reference):
- Plains: Maximum temperature ≥40°C AND at least 4.5°C above normal → declared heatwave
- Coastal stations: Maximum temperature ≥37°C AND at least 4.5°C above normal
- Hills: Maximum temperature ≥30°C AND at least 4.5°C above normal
- Severe Heatwave: Departure from normal ≥6.4°C OR absolute max ≥45°C
UPSC synthesis: Heatwave 2024 = GS3 climate economics + GS2 labour + GS1 temperature extremes. Key exam facts: 247 billion labour hours lost; $194 billion economic losses; 44,000+ heatstroke cases; 380 million workers (75% workforce) exposed to heat-intensive outdoor work; Delhi informal workers earnings fell ~40% on peak heat days; 4.5% GDP at risk by 2030; NDMA prep started October 2023 (unusually early); national workshop February 2024; DDMA Delhi HAP 2024-25 released April 2024 (800+ cooling centres, colour-coded alerts, ASHA door-to-door); IMD heatwave = plains max ≥40°C + 4.5°C above normal; severe = 6.4°C departure or ≥45°C absolute. Distinguish from Cl6 content (which covered deaths/peak temperatures); this is the ECONOMIC and LABOUR productivity angle.
Exam Strategy
Prelims traps:
- Mawsynram (not Cherrapunji) holds the current average annual rainfall record. Cherrapunji holds historic single-event records.
- Tamil Nadu receives peak rainfall from the NE monsoon (Oct–Dec), not the SW monsoon — opposite of most of India. This is a very common Prelims question.
- Loo blows from west/northwest; is a dry wind (not humid); is a local wind specific to the Indo-Gangetic Plains.
- Kal Baisakhi = West Bengal/Assam; Mango showers = Kerala/Karnataka; Cherry blossom showers = Assam — these local names are tested.
- The SW Monsoon onset is at Kerala (~June 1); withdrawal begins from northwest Rajasthan (~mid-September).
- Monsoon arrives at Delhi around June 27–July 1 — not June 1.
Mains angles:
- Monsoon variability and India's food security — how deficit/excess monsoons affect different crop systems
- Western Disturbances — underappreciated climate system; their weakening linked to climate change
- India's NDC commitments — feasibility, progress, gaps
- NE monsoon and Tamil Nadu's unique vulnerability (cyclones + rainfall concentration in a few months)
Practice Questions
Prelims:
With reference to the monsoon of India, which of the following statements is/are correct?
- The onset of the southwest monsoon is first experienced in Tamil Nadu.
- Tamil Nadu receives most of its rainfall from the northeast monsoon.
- Mawsynram in Meghalaya is the wettest place in India by average annual rainfall.
(a) 1 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3
- The onset of the southwest monsoon is first experienced in Tamil Nadu.
"Kal Baisakhi" refers to which of the following?
(a) A local wind of Rajasthan similar to the Loo
(b) Pre-monsoon thunderstorms in West Bengal and Assam
(c) The first burst of the southwest monsoon over Kerala
(d) Snowfall in Himachal Pradesh during Western Disturbances
Mains:
Analyse the factors responsible for the spatial and temporal variability of the Indian monsoon. How does this variability affect the agricultural economy of India? (CSE Mains 2021, GS Paper 1, 15 marks)
Discuss India's Nationally Determined Contributions (NDCs) and evaluate the challenges India faces in meeting its climate commitments under the Paris Agreement. (CSE Mains 2022, GS Paper 3, 15 marks)
