Rainfall Distribution and Climatic Regions of India
Spatial and seasonal rainfall in India, LPA and IMD categories, variability, rain shadow, Koeppen climatic regions and the Chhattisgarh rainfall pattern.
Prerequisites
- Mechanism of the Indian Monsoon — the two branches explain most of the pattern on the map.
- Seasons of India — when the rain falls.
- Physiography of India — windward and leeward slopes.
The Hook: Same Monsoon, Very Different Rain
In an average year, a village on the Bastar plateau gets noticeably more rain than a village near Kawardha in the western Chhattisgarh plain, even though both lie in the same state and the same monsoon reaches both. Across India the contrast is far sharper: a place in the Khasi hills can receive in a year more than a hundred times what Leh receives.
How is India’s rainfall spread across space and seasons, how reliable is it, and how do we measure whether a monsoon was “normal”?
Why it matters: Prelims asks the highest and lowest rainfall places, rainfall gradients, IMD categories and the Koeppen types. Mains GS-III asks about variability, drought and the link between rainfall and agriculture, often with a Chhattisgarh angle.
The Numbers: LPA and Seasonal Share
| Measure | Value |
|---|---|
| All-India annual rainfall, LPA (1971–2020) | 1,160.1 mm (about 116 cm) |
| South-west monsoon (June–September), LPA (1971–2020) | 868.6 mm (about 87 cm) |
| Share of the south-west monsoon in annual rain | About 75% (868.6 ÷ 1,160.1) |
| Previous south-west monsoon LPA (1961–2010) | About 88 cm (880.6 mm), replaced from 2022 |
Long Period Average (दीर्घावधि औसत, LPA): the average rainfall of a region over a long base period (now 1971–2020). Each season’s rain is expressed as a percentage of the LPA.
The remaining quarter of the annual rain comes mostly in the pre-monsoon (March–May) and post-monsoon (October–December) months; the winter (January–February) share is only a few per cent.
IMD categories for all-India seasonal rainfall
| Category | Rainfall as % of LPA |
|---|---|
| Deficient | Less than 90% |
| Below normal | 90–95% |
| Normal | 96–104% |
| Above normal | 105–110% |
| Excess | More than 110% |
The five categories above are the ones IMD uses in its forecasts. When summing up a finished season, IMD and the media often use a simpler three-way rule: within ±10% of the LPA is “normal”, below 90% is deficient and above 110% is excess. That is why a season at 94% of LPA (2023) was described as “normal” even though it falls in the “below normal” forecast band. A deficient all-India season (below 90%) is commonly treated as an all-India drought year.
For districts and meteorological subdivisions IMD uses different bands: normal = within −19% to +19% of the normal, deficient = −20% to −59%, excess = +20% or more, and larger shortfalls are “large deficient” or “scanty”.
Recent seasons (dated facts)
| Year | South-west monsoon (% of LPA) | Note |
|---|---|---|
| 2023 | About 94% | El Niño year; a positive IOD helped limit the deficit |
| 2025 | About 108% | Above the LPA |
| 2026 | About 87% (759.4 mm; deficit of about 12.6%) | Deficient; the lowest since 2015, in a developing strong El Niño year. IMD’s April and May forecasts (92% and 90%) were both higher. East and north-east India was reported to have had its driest monsoon since records began in 1901 |
(Figures as reported by IMD at the end of each season; see the flags file for how they were checked.)
Spatial Distribution
| Rainfall zone | Annual rainfall | Areas |
|---|---|---|
| Very high | More than 200 cm | West coast and the windward Western Ghats; sub-Himalayan areas of the north-east and the hills of Meghalaya; Andaman and Nicobar Islands |
| Moderately high | 100–200 cm | Southern Gujarat, east Tamil Nadu, the north-eastern peninsula (Odisha, Jharkhand, Chhattisgarh, eastern Madhya Pradesh), Bihar, West Bengal, the Ganga plain along the sub-Himalaya, Cachar valley and Manipur |
| Low | 50–100 cm | Western Uttar Pradesh, Delhi, Haryana, Punjab, Jammu, eastern Rajasthan, Gujarat and the interior Deccan plateau |
| Inadequate | Less than 50 cm | Western Rajasthan, Ladakh, parts of Gujarat (Kachchh) and the rain-shadow interiors of Maharashtra, Karnataka and Andhra Pradesh |
Extremes
| Record | Place |
|---|---|
| Highest average annual rainfall | Mawsynram (Meghalaya), about 11,800 mm or more a year; often cited as the wettest place on Earth |
| Historical one-year and one-month records | Cherrapunji (Sohra), Meghalaya |
| Lowest rainfall | Leh in Ladakh (a cold desert) and western Rajasthan around Jaisalmer and Barmer |
Gradients to remember
- In the northern plains, rainfall decreases from east to west (Kolkata > Patna > Varanasi > Delhi > Bikaner) as the Bay of Bengal branch loses moisture moving up the Ganga plain.
- In the peninsula, rainfall decreases from west to east across the Western Ghats: very heavy on the windward coast, low on the leeward Deccan (Mumbai vs Pune).
- In the north-east, rainfall decreases from south to north and also with distance from the Bay in the plains, but the windward hill slopes are very wet.
- The Tamil Nadu coast is the exception: most of its rain comes in October–December.
Rain shadow (वर्षा छाया क्षेत्र)
A rain shadow is the dry, leeward side of a mountain. Moist air rises and rains on the windward side; descending air on the leeward side warms and dries.
| Mountain | Wet windward side | Rain-shadow side |
|---|---|---|
| Western Ghats | Konkan and Malabar coasts (Mumbai, Mangaluru) | Interior Maharashtra and Karnataka (Pune, Marathwada, north Karnataka) |
| Khasi hills | Mawsynram, Cherrapunji | Shillong plateau interior |
| Maikal range (Chhattisgarh) | Eastern slopes | Western Chhattisgarh plain (Kabirdham, Bemetara), drier and more drought-prone |
Variability of Rainfall
Variability is measured by the coefficient of variation (CV): the standard deviation of annual rainfall as a percentage of the mean. High CV means unreliable rain.
| CV | Areas |
|---|---|
| Less than 25% (most reliable) | West coast, Western Ghats, north-eastern peninsula, eastern Ganga plain, north-east India, Uttarakhand, Himachal Pradesh, parts of Jammu and Kashmir |
| 25–50% | Most of the rest of the country |
| More than 50% (least reliable) | Western Rajasthan, northern Jammu and Kashmir / Ladakh, interior parts of the Deccan plateau |
Climatic Regions: The Koeppen Scheme
Wladimir Koeppen’s classification uses temperature and precipitation, with letter codes. NCERT applies it to India as follows:
| Type | Meaning | Areas |
|---|---|---|
| Amw | Monsoon with short dry season | West coast south of Goa |
| As | Monsoon with dry summer (rain in winter) | Coromandel coast of Tamil Nadu |
| Aw | Tropical savanna (dry winter) | Most of the peninsular plateau south of the Tropic of Cancer |
| BShw | Semi-arid steppe | Parts of Rajasthan, Haryana and Gujarat |
| BWhw | Hot desert | Extreme western Rajasthan |
| Cwg | Monsoon with dry winter | Ganga plain, eastern Rajasthan, northern Madhya Pradesh, most of north-east India |
| Dfc | Cold humid winter with short summer | Arunachal Pradesh |
| E | Polar type | High Himalaya: Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand |
Letter key: A tropical humid, B dry, C warm temperate, D cold snow-forest, E polar; small letters: w dry winter, s dry summer, m monsoon, h hot dry, g Ganges-type temperature regime (hottest month before the summer solstice), f no dry season, c cool short summer.
Chhattisgarh’s Rainfall Pattern
| Fact | Detail |
|---|---|
| Average annual rainfall | About 1,200–1,300 mm (studies give slightly different long-term averages) |
| Monsoon share | Most of the year’s rain, roughly 85–90%, falls in June–September |
| Wettest part | Bastar plateau (south); the Abujhmarh hills are among the wettest |
| Driest part | Western plain in the lee of the Maikal range (Kabirdham, Bemetara) |
| Main source | Bay of Bengal branch and its depressions moving along the monsoon trough |
So the state’s rainfall is in the 100–200 cm zone, is relatively reliable compared with western India, but is concentrated in four months. Dry spells in July–August and a weak September still cause agricultural drought in rain-fed paddy areas. See Climate and Soils of Chhattisgarh and Agriculture and Irrigation in Chhattisgarh.
Analysis: Rainfall, Drought and Floods (Mains material)
- Concentration: about three-quarters of the year’s rain falls in four months, so water must be stored (reservoirs, tanks, groundwater recharge) for the other eight. This is the case for watershed development and traditional tanks, including Chhattisgarh’s village ponds.
- Types of drought: meteorological (rainfall well below normal), hydrological (falling surface and groundwater) and agricultural (soil moisture too low for crops). A normal all-India season can still leave districts in agricultural drought.
- Floods and droughts in the same year: heavy rain in the north-east and the Himalaya can coincide with drought in the peninsula, especially during breaks.
- Climate change: official assessments (Ministry of Earth Sciences, 2020) report a decline in summer monsoon rainfall over the second half of the twentieth century and a rise in extreme rainfall events. Expect more intense short spells and longer dry gaps.
- Policy responses: rainfed-area development, crop insurance (PMFBY), contingency crop plans, micro-irrigation, district-level forecasts and drought manuals.
Memory Tricks
Don’t Confuse
| This | vs | That |
|---|---|---|
| Mawsynram — highest average annual rainfall | vs | Cherrapunji (Sohra) — historical one-year and one-month records |
| Leh — lowest rainfall, cold desert (E/B type) | vs | Jaisalmer–Barmer — low rainfall, hot desert (BWhw) |
| As — Coromandel coast, rain in winter | vs | Amw — west coast south of Goa, short dry season |
| All-India normal — 96–104% (forecast), or within ±10% in season summaries | vs | District normal — within ±19% |
| LPA 87 cm — June–September | vs | LPA about 116 cm — whole year |
Common Mistakes
- “Rainfall in the Ganga plain increases from east to west.” It decreases from east to west.
- “The LPA for the south-west monsoon is 88 cm.” That was the old (1961–2010) value. Since 2022 it is 87 cm (1971–2020).
- “The Coromandel coast is type Aw.” NCERT gives it As (dry summer, winter rain).
- “Low-rainfall areas have low variability.” The reverse: low rainfall goes with high variability.
- “Chhattisgarh is a low-rainfall state.” It is in the 100–200 cm zone; its problem is concentration and dry spells, not a low total.
Practice
All questions below are original practice questions written in CGPSC style. They are not previous-year questions.
Level 1: Foundation
- The base period of IMD’s current Long Period Average is ______.
- The Koeppen climate type of the Coromandel coast is ______.
- A season with less than ______% of the LPA is called deficient.
Answers
- 1971–2020.
- As.
- 90.
Level 2: Prelims MCQs
Q1. Consider the following statements:
- The south-west monsoon contributes about three-quarters of India’s annual rainfall.
- The Long Period Average of all-India south-west monsoon rainfall based on 1971–2020 is about 87 cm.
- Areas of low rainfall in India generally have low variability of rainfall.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer and explanation
Q2. Match List I (Koeppen type) with List II (Region):
| List I | List II |
|---|---|
| A. Amw | 1. Arunachal Pradesh |
| B. BWhw | 2. Ganga plain |
| C. Cwg | 3. West coast south of Goa |
| D. Dfc | 4. Extreme western Rajasthan |
- (a) A-3, B-4, C-1, D-2
- (b) A-3, B-4, C-2, D-1
- (c) A-4, B-3, C-2, D-1
- (d) A-2, B-4, C-3, D-1
Answer and explanation
Q3. The western part of the Chhattisgarh plain (Kabirdham–Bemetara area) receives less rain than the Bastar plateau mainly because:
- (a) It receives rain only from the north-east monsoon
- (b) It lies in the lee of the Maikal range, and the Bay of Bengal winds have lost moisture by the time they reach it
- (c) It lies north of the Tropic of Cancer
- (d) It is affected by western disturbances in summer
Answer and explanation
Q4. Which one of the following regions has a coefficient of variation of annual rainfall of more than 50%?
- (a) Konkan coast
- (b) North-eastern peninsula
- (c) Western Rajasthan
- (d) Eastern Ganga plain
Answer and explanation
Q5. India’s south-west monsoon rainfall in 2026 was about 87% of the LPA. Under IMD’s categories, this season is classified as:
- (a) Normal
- (b) Below normal
- (c) Deficient
- (d) Above normal
Answer and explanation
Level 3: Mains Answer Writing
Q1. (150–200 words) “The problem of Indian rainfall is not its quantity but its distribution and variability.” Discuss.
Model answer outline
- Intro: India’s annual LPA is about 116 cm, above the world land average, yet droughts recur.
- Body:
- Temporal concentration: about 75% of rain in June–September; long dry season; breaks within the monsoon.
- Spatial unevenness: over 1,100 cm at Mawsynram vs under 10–15 cm in Ladakh and western Rajasthan; east–west gradient in the north, west–east in the peninsula.
- Variability: CV below 25% on the west coast and north-east, above 50% in western Rajasthan; low rain and high variability go together.
- Consequences: drought and floods in the same season; rain-fed farming risk; reservoir dependence.
- Responses: storage, watershed management, crop diversification, forecasts, crop insurance.
- Chhattisgarh angle: the state gets 1,200–1,300 mm a year, but concentration in four months and July–August dry spells cause drought in the rain-fed western plain.
- Conclusion: managing timing and storage matters more than increasing the quantity of rain.
Q2. (60 words) What is a rain shadow area? Give two examples from India.
Model answer outline
- The dry leeward side of a mountain: rising moist air rains on the windward side; descending air warms and dries.
- Examples: the interior Deccan (Pune, Marathwada) behind the Western Ghats; the western Chhattisgarh plain behind the Maikal range; Shillong behind the Khasi hills’ southern crest.
Quick Revision Table
| Fact | Detail |
|---|---|
| Annual LPA (1971–2020) | 1,160.1 mm |
| June–September LPA (1971–2020) | 868.6 mm (87 cm); old value 88 cm |
| Monsoon share | About 75% of annual rain |
| IMD categories | <90 deficient; 90–95 below normal; 96–104 normal; 105–110 above normal; >110 excess |
| District / subdivision normal | Within ±19% |
| 2026 season | About 87% of LPA (deficient), lowest since 2015 |
| Wettest | Mawsynram (average); Cherrapunji (historical records) |
| Driest | Leh (Ladakh), western Rajasthan |
| North India gradient | Decreases east to west |
| Peninsula gradient | Decreases west to east |
| High variability (>50%) | Western Rajasthan, Ladakh, interior Deccan |
| Koeppen | Amw west coast; As Coromandel; Aw plateau; BWhw west Rajasthan; Cwg Ganga plain; Dfc Arunachal; E high Himalaya |
| Chhattisgarh | 1,200–1,300 mm; wettest Bastar; driest western plain; mostly Aw |
Key Takeaways
- India’s annual LPA is 1,160.1 mm; the June–September LPA is 868.6 mm (87 cm), about three-quarters of the year’s rain.
- Rain decreases east to west in the north and west to east in the peninsula; Mawsynram is the wettest, Leh and western Rajasthan the driest.
- Low rainfall goes with high variability; western Rajasthan is the classic case.
- IMD’s bands: below 90% deficient, 96–104% normal, above 110% excess. The 2026 season (about 87%) was deficient.
- Chhattisgarh is in the 100–200 cm zone; its risk lies in concentration and dry spells, especially in the western plain.
What’s Next
- El Niño, La Niña and the Indian Ocean Dipole — what drives good and bad years
- Soils and Natural Vegetation of India — rainfall maps onto forest types and soils
- Drainage of India — monsoon-fed rivers and floods
- Agricultural Economy — rain-fed farming, drought and insurance
- Climate and Soils of Chhattisgarh