Physical Geography · Topic 11 · GS Paper 1

World Climate Classification — Köppen · Trewartha · Thornthwaite

Long-term averages of temperature, precipitation and their seasonality divide Earth's surface into a small number of recurring climate types. The most enduring scheme — Wladimir Köppen's 1918 system — uses two-letter codes (Af, Aw, BWh, Cfa, Cwg, Dfc, ET, EF) that mirror the world's natural vegetation belts. Glenn Trewartha (1968) refined the boundaries; C. W. Thornthwaite (1948) built a rival quantitative system on the P/E ratio. This topic walks through all three with climographs, world map, and India's full Köppen breakdown, paired with neatly labelled diagrams and separate Prelims and Mains question banks.

Physical Geography · Topic 11 · ~36 min read · Updated June 2026

Why this topic matters for UPSC

Prelims: NCERT-anchored MCQs on Köppen criteria (vegetation-based, T & P thresholds) · the five main groups A, B, C, D, E · second letter (f, w, s, m) and third letter (a, b, c, d, h, k) meaning · key codes (Aw savanna, Amw monsoon, BSh tropical steppe, BWh hot desert, Cfa humid sub-tropical, Cs Mediterranean, Cwg China-type / India monsoon, Df continental, ET tundra, EF ice-cap) · Trewartha modification (Group H highland, Cs split) · Thornthwaite's P/E and T/E indices · climograph interpretation · India in Köppen.

Mains GS-1 & GS-3: "Critically evaluate the Köppen classification of world climates" · "Compare Köppen and Thornthwaite systems" · "Discuss the climatic regions of India based on Köppen's classification" · "How is climate change shifting Köppen boundaries?" · "Why is Mediterranean climate confined to west coasts of continents in subtropical latitudes?" — and many more.

Why classify climates · criteria
Early classifiers — Greek to Supan
Köppen system — 5 groups + letter codes
11 Köppen climate types in detail
Trewartha modification (1968)
Thornthwaite system — P/E ratio
Reading a climograph
World distribution of climates
India in Köppen — 9 sub-types
Climate change & shifting boundaries
PYQs (Prelims + Mains, separate)
Revision — 15 key facts

1 · Why classify climates · criteria

Climate (WMO definition) = the statistical aggregate of weather over a long period, conventionally 30 years. Weather is the instantaneous state of the atmosphere; climate is its long-term character. Earth has thousands of unique local climates — too many to study individually — so geographers group them into a small number of climate types with shared temperature, precipitation and seasonality patterns.

Purpose of climate classification

Pattern recognition — reveal latitudinal and longitudinal order in a complex world.
Predictive power — knowing a place's climate type lets us infer its likely vegetation, soils, agriculture, water budget, energy demand, disease ecology.
Comparison — link Mediterranean basin to California, Cape Town, central Chile and SW Australia for cross-regional learning.
Boundary-mapping — track climate-zone shifts under warming, desertification, monsoon variability.
Resource planning — irrigation design, cropping calendars, urban heat-stress codes.

Three classification approaches are recognised in climatology:

Empirical (genetic-empirical) — uses observed temperature and precipitation as primary criteria. Examples: Köppen, Trewartha. Strength: simple, vegetation-aligned. Weakness: ignores causes.
Applied (water-budget) — uses derived indices like PET, P/E ratio, moisture deficit. Example: Thornthwaite. Strength: quantitatively rigorous. Weakness: needs more data; complex codes.
Genetic (causal) — uses underlying atmospheric circulation (air masses, fronts, pressure belts). Examples: Flohn (1950), Strahler (1969). Strength: explains why. Weakness: lacks crisp boundaries.

Two questions every classification must answer: (1) What variables to use? (T, P, vegetation, air mass) (2) Where to draw boundaries? Köppen chose vegetation-aligned thresholds; Thornthwaite chose water-balance ratios; Strahler chose air-mass dominance. None is universally "correct" — each suits a different purpose.

2 · Early classifiers — from Aristotle to Supan

The idea of dividing Earth into climate zones is ancient. The first systematic attempt is credited to the Ancient Greeks:

Greek 3-zone scheme (Aristotle, ~350 BCE)

Torrid zone — between the Tropics of Cancer and Capricorn (23.5°N–23.5°S); too hot to live, allegedly uninhabitable.
Temperate zones (×2) — between the tropics and the polar circles in each hemisphere; the "habitable" belts.
Frigid zones (×2) — beyond the polar circles (66.5°); too cold for life.

The scheme rested on the angle of the Sun alone, used by Aristotle's Meteorologica. Crude but it survived for 2 000 years and seeded the modern term "climate" — from Greek klima (slope/incline of the Sun's rays).

Modern empirical classification began in the late 19th century with European geographers seeking sharper criteria:

Classifier · year	Basis / contribution
A. Supan, 1879	First modern scheme — divided world into 35 climate provinces using 20 °C isotherm of warmest month and 10 °C of coldest. Introduced numerical thresholds, replacing Greek zones.
W. Köppen, 1884	Published first vegetation-aligned scheme; used 5 thermal zones. Revised 1900, 1918, 1936. The 1918 system with 2-letter codes is the canonical Köppen still taught today.
A. Penck, 1910	Proposed a humidity-based system splitting world into 3 climate groups (humid, arid, nival) by relation of P and evaporation.
C. W. Thornthwaite, 1931 & 1948	Built a rigorous quantitative scheme based on P/E (precipitation-effectiveness) ratio and T/E (temperature-efficiency) ratio. Calculated PET. The 1948 revision is the standard.
H. Flohn, 1950	Genetic classification linking climates to wind belts and air-mass dominance — explains why a climate exists.
G. T. Trewartha, 1968	Modified Köppen — simplified codes, added Group H (highland) for mountain climates, redefined some boundaries (e.g., Cs split into Csa/Csb based on summer T).
A. N. Strahler, 1969	Genetic scheme grouping climates under three air-mass regimes: low-latitude (equatorial & tropical), mid-latitude, high-latitude.
Peel, Finlayson, McMahon, 2007	Updated Köppen-Geiger world map using high-resolution gridded climate data — the version cited in modern climate-change literature.

Why Köppen still dominates UPSC: NCERT XI uses Köppen. The codes (Aw, Cfa, BWh) are mnemonic. It aligns with biomes/vegetation — easy to integrate with botany, agriculture, ecology. Trewartha and Thornthwaite are tested as modifications/alternatives, not as primary frameworks.

3 · Köppen system — 5 main groups + letter codes

Wladimir Köppen (Russian-German botanist-climatologist, 1846–1940) published his world climate classification in 1884 and refined it in 1918 and 1936. His central insight: natural vegetation is the best long-term integrator of climate. Where a tropical rainforest grows, the climate is wet and warm year-round; where tundra grass survives, the warmest month is between 0 and 10 °C. So he drew climate boundaries to match vegetation boundaries — and then expressed those boundaries as crisp T & P thresholds.

The 5 main groups (capital letter)

A — Tropical (megathermal) · coldest month ≥ 18 °C · no winter · rainforest, savanna.
B — Dry (arid) · evaporation > precipitation · uses a P-threshold formula (varies by T & rainfall regime) · deserts & steppes.
C — Warm temperate (mesothermal) · coldest month between +18 °C and –3 °C; warmest > 10 °C · mild winters · Mediterranean, humid sub-tropical, marine west-coast.
D — Cold continental (microthermal) · coldest month < –3 °C; warmest > 10 °C · severe winters · humid-continental + sub-arctic taiga.
E — Polar · warmest month < 10 °C · no true summer · tundra, ice-cap.

Mnemonic for boundaries: 18 / –3 / 10 — the three magic numbers that separate A↔C, C↔D and D↔E respectively. B is independent (depends on P, not just T).

Second letter describes precipitation seasonality (for A, C, D) or aridity level (for B) or polar sub-type (for E):

f — feucht = wet · no dry season (Af, Cf, Df)
m — monsoon · short dry season but heavy annual P (Am)
w — winter dry · dry season at low sun (Aw, Cw, Dw)
s — summer dry · dry at high sun (Cs, Ds — rare)
W (capital) — desert (BW)
S (capital) — steppe/semi-arid (BS)
T — tundra (ET): warmest 0 to 10 °C
F — frost / ice-cap (EF): warmest < 0 °C

Third letter (optional) refines summer warmth or winter cold:

a — hot summer (warmest ≥ 22 °C) → Cfa, Dfa
b — warm summer (warmest < 22 °C but ≥ 4 months above 10 °C) → Cfb, Dfb
c — cool/short summer (1–3 months > 10 °C) → Dfc, Dwc
d — very cold winter (< –38 °C) → Dfd (Verkhoyansk, Yakutia)
h — hot dry (mean annual T > 18 °C) → BWh, BSh
k — cold dry (mean annual T < 18 °C) → BWk, BSk
g — Gangetic-type — hottest month before solstice rains arrive (Indian-Köppen addition) → Cwg

Fig 11.1 — Köppen decision tree. Test aridity first (gives B), then tropical (A), then polar (E), then continental cold (D); whatever remains is C. Add a second letter for precipitation seasonality and an optional third letter for summer warmth / winter cold. Example: Delhi → not arid → coldest 14 °C (not A) → warmest 33 °C (not E) → coldest above –3 (not D) → C; winter dry & hot summer → Cwa (Köppen-Geiger) / Cwg (Indian convention).

Magic-number mnemonic: 18 / –3 / 10 — the three temperature thresholds. ≥ 18 → tropical (A) · < –3 → continental cold (D) · < 10 warmest → polar (E) · everything else & not dry → warm temperate (C). B comes from the precipitation formula, not temperature.

4 · The 11 Köppen climate types in detail

Combining the five main groups with second/third letters gives ~11 internationally used climate types. Each has a signature temperature regime, precipitation pattern, vegetation, location and Indian / world example.

Code	Name	T & P signature	Vegetation	Locations
Af	Tropical rainforest	Coldest ≥ 18 °C · every month ≥ 60 mm · no dry season · annual P 1 500–2 500 mm	Evergreen multi-storied rainforest · epiphytes · lianas	Amazon · Congo · Indonesia · S Kerala (margin) · Sumatra
Am	Tropical monsoon	Coldest ≥ 18 °C · short dry season < 60 mm but very wet rest (annual > 1 500 mm)	Tropical evergreen / semi-evergreen forest	Western Ghats coast · NE India (Meghalaya, Assam) · coastal Myanmar · W African coast
Aw	Tropical savanna (winter dry)	Coldest ≥ 18 °C · 4–6 month winter dry season · summer wet · annual P 500–1 500 mm	Tall-grass savanna · scattered trees (acacia, baobab)	Sahel · East-African savanna · Central Brazil cerrado · most of Indian peninsula (S of Vindhyas)
BWh	Hot desert	Evap ≫ precip · annual T > 18 °C · summer T > 38 °C · annual P < 250 mm	Sparse xerophytes · halophytes	Sahara · Arabian · Thar (W Rajasthan) · Kalahari · Sonoran · Australian interior
BSh	Hot semi-arid (steppe)	Same as BWh but P 250–500 mm · single brief rainy season	Short grasses · thorn-scrub	Sahel transition · Marathwada · Rayalaseema · NE Africa · Brazilian sertão
BWk	Cold desert	Annual T < 18 °C · severe winter · P < 250 mm	Sparse cold-tolerant scrub	Gobi · Patagonia · Ladakh (cold high-altitude desert) · Tarim basin · Atacama (cool coastal)
BSk	Cold steppe	Annual T < 18 °C · P 250–500 mm	Short steppe grass	Central Asian steppe · US Great Plains (west) · Patagonia margins
Cfa	Humid sub-tropical	Coldest –3 to 18 °C · warmest ≥ 22 °C · year-round P 750–1 500 mm	Mixed broadleaf / pine	SE USA · S China · S Brazil · E Australia · E Gangetic plain (Bihar, W Bengal partly)
Cfb	Marine west-coast (oceanic)	Mild winters · cool summers (warmest < 22 °C) · year-round rain 500–2 500 mm · cloudy	Mixed deciduous-coniferous	NW Europe (UK, France, Germany, Norway) · British Columbia · S Chile · NZ · Tasmania
Csa / Csb	Mediterranean (dry summer)	Coldest –3 to 18 °C · warm-dry summer · mild wet winter · annual P 400–900 mm	Sclerophyll evergreen (olive, oak, cork) · maquis · chaparral	Mediterranean basin · California · central Chile · Cape Town · SW Australia (Perth)
Cwa / Cwg	Monsoon humid sub-tropical (winter dry)	Coldest –3 to 18 °C · dry winter · hot wet summer (monsoon) · annual P 750–1 500 mm	Deciduous forest, grassland	N India Ganga plain (Delhi, Kanpur, Lucknow) · S China · N Vietnam · highlands of E Africa
Dfa / Dfb	Humid continental	Coldest < –3 °C · warmest > 10 °C · year-round P · cold snowy winters	Mixed forest, prairie	NE USA, Great Lakes · E Europe · NE China · Korea (north)
Dfc / Dwc	Sub-arctic / Taiga (boreal)	Coldest < –3 °C · 1–3 months > 10 °C · short cool summer · large annual range	Coniferous evergreen taiga (spruce, fir, pine, larch)	Russia (Siberia) · Canada (Yukon, NWT) · Scandinavia (interior) · Alaska
ET	Tundra	Warmest month 0 to 10 °C · permafrost · scant P	Mosses, lichens, dwarf shrubs · no trees	N Canada · N Russia · coastal Greenland · Svalbard · Tibetan plateau margin
EF	Ice-cap	Warmest month < 0 °C · permanent snow / ice cover · katabatic winds	None (lichens on rare nunataks)	Antarctica (interior) · Greenland ice-sheet · high-Arctic islands

Two-letter quick memory: first letter = heat; second = rain pattern. Cs = Cool-temperate, summer-dry → Mediterranean. Aw = Tropical, winter-dry → Savanna. Dfc = cold continental, year-wet, cool summer → Taiga. Once you internalise these doublets, the whole world map decodes itself.

5 · Trewartha modification (1968)

Glenn T. Trewartha (American climatologist) refined Köppen in his book An Introduction to Climate (1968 edition). His complaint: Köppen's C group is too broad — it lumps mild Mediterranean Athens with cool oceanic London with sub-tropical Shanghai. He also wanted a separate category for high mountains, which Köppen forced into surrounding lowland codes.

Trewartha's main changes

Added Group H — Highland climates. Climates above ~1 500 m where altitude over-rides latitude. Vertical zonation produces multiple climate belts within a small horizontal distance. Examples: Andes, Rockies, Tibetan plateau, Ethiopian highlands, E African plateau, Western Ghats & Himalayan slopes in India.
Split C group into Cs (subtropical dry-summer = Mediterranean), Cf (subtropical humid), and Do (temperate oceanic) — using temperature of warmest and coldest months more carefully.
Six groups instead of five for low- and mid-latitude climates: A (tropical), B (dry), C (subtropical), D (temperate), E (boreal), F (polar) — note F replaces E as polar, while E becomes boreal/sub-arctic. (UPSC tip: stick with Köppen letter-meanings unless question explicitly asks "Trewartha".)
Sharper boundaries using more recent data and additional thresholds (e.g., 8-month-mean isotherms for tropical/subtropical division).
Universal Thermal Climate Classification companion — uses month-count above 10 °C as primary indicator of growing season.

Why Trewartha matters for India: Köppen pushes the Himalayan zone into "E" (polar) or "H" by default; Trewartha's explicit H group is a far better fit for Himalayan vertical zonation — sub-tropical foothills → temperate mid-slopes → alpine meadow → glacier — telescoped into 200 km horizontal distance.

UPSC framing: Köppen 1918 still the default world scheme; Trewartha 1968 is the highland-aware refinement. Both are empirical and vegetation-aligned. Differences appear at boundaries (e.g., Trewartha's tropical-subtropical line uses 8 months > 10 °C; Köppen's uses 18 °C coldest-month).

6 · Thornthwaite system — P/E ratio (1948)

Charles Warren Thornthwaite (American geographer-climatologist, 1899–1963) built a fundamentally different classification in 1931 and revised it in 1948. His system is applied / water-budget based — uses derived moisture and thermal indices calculated from observed T and P, plus computed PET. The system is more rigorous than Köppen but harder to memorise.

The two key indices

Precipitation-Effectiveness (P/E) ratio — measures moisture availability. For each month: P/E = 1.65 × (P / (T + 12.2))^10/9, then summed for 12 months → P/E index. Higher = wetter.
Temperature-Efficiency (T/E) ratio — measures thermal energy available for plant growth, based on accumulated monthly T above 0 °C. Higher = warmer.
Moisture Index (I_m) (1948 revision) = 100 × (S – D) / PET, where S = surplus, D = deficit. Positive = humid, negative = arid.
Thermal Efficiency Index (TE) = sum of monthly PET in cm. Higher = warmer climate.

Thornthwaite's 1948 climate classes (based on moisture index I_m):

Code	Class	I_m range
A	Per-humid	≥ 100
B₄–B₁	Humid (4 sub-classes)	20 to 100
C₂	Moist sub-humid	0 to 20
C₁	Dry sub-humid	–33 to 0
D	Semi-arid	–67 to –33
E	Arid	≤ –67

For thermal efficiency, parallel classes A′ (megathermal) → B′₄–B′₁ (mesothermal) → C′₂–C′₁ (microthermal) → D′ (tundra) → E′ (frost) are added. A station code therefore looks like B₂B′₃rb′₄ — humid mesothermal with small seasonal water variation. The system's strength is precision; its weakness is unreadability.

Köppen vs Thornthwaite — comparison

Aspect	Köppen 1918	Thornthwaite 1948
Approach	Empirical (T, P thresholds)	Applied (water budget, PET)
Primary input	Monthly T, P	Monthly T, P + computed PET
Vegetation link	Strong (boundaries match biomes)	Indirect (via moisture surplus/deficit)
Codes	Short (Aw, Cfa) — memorable	Long (B₂B′₃rb′₄) — complex
Mountain handling	Poor — needs Trewartha's H	Better — moisture index adjusts
UPSC weight	Very high (NCERT base)	Medium (asked as "alternative")
Best use	Pattern recognition, biome study	Hydrology, irrigation, agriculture planning

7 · Reading a climograph

A climograph (climate diagram) is the single most powerful tool to identify a station's Köppen class at a glance. Convention: monthly temperature drawn as a red line plotted against the left Y-axis (°C); monthly precipitation drawn as blue bars against the right Y-axis (mm); X-axis = 12 months Jan→Dec. Annual totals, mean T and climate code are placed in the header.

How to read a climograph in 4 steps

Coldest-month T → fix main group: ≥ 18 °C = A · –3 to 18 = C · < –3 = D · warmest < 10 = E.
Total annual P + aridity formula → if below threshold, override to group B.
Seasonal P pattern → if dry season at low sun (winter) → "w"; high sun (summer) → "s"; no dry month → "f"; short dry but very wet rest → "m".
Warmest-month T → "a" if ≥ 22 °C; "b" if < 22 but 4+ months > 10; "c" if 1–3 months > 10.

Af. BENGALURU Aw: Red 21–28 °C (always > 18) · bars near-zero Dec–Mar, peak JJAS → A, winter-dry = w → Aw (tropical savanna). ROME Csa: Coldest Jan ~8 °C (between –3 & 18 = C) · warmest Jul ~25 °C (≥ 22 = a) · summer dry pattern → Csa (Mediterranean). DELHI Cwa / Cwg: Coldest Jan ~14 °C (C) · warmest May ~33 °C (a) · winter dry · monsoon peak Jul-Aug → Cwa; Indian convention "g" since hottest month before solstice rains → Cwg. VERKHOYANSK Dfd: Coldest Jan ~–48 °C (< –38 = d) · warmest Jul ~+16 °C (> 10 → D not E) · year-round P → Dfd (most extreme annual range on Earth, ≈ 64 °C).

Fig 11.2 — Five climographs covering the main Köppen quadrants. Notice how the shape of the red T-line and the distribution of the blue P-bars are diagnostic. Singapore (flat red, fat blue) = Af; Rome (mountain-shaped red, U-shaped blue) = Csa; Verkhoyansk (deep-V red) = Dfd — earth's biggest annual T swing.

8 · World distribution of climates

The Köppen climates form recognisable global belts whose latitude position is set by the planetary pressure-wind system (ITCZ → equatorial wet · subtropical highs → deserts · westerlies → mid-lat wet · polar high → ice) and whose longitudinal asymmetry is set by ocean currents and continentality.

Fig 11.3 — Schematic latitudinal sweep of Köppen climates. Equatorial Af belt → tropical Am/Aw → subtropical desert BWh/BSh → C-group split (Csa Mediterranean west, Cfa humid east, Cwa monsoon east) → continental Df → sub-arctic Dfc → ET tundra → EF ice-cap. SH bands are narrower because of less land area.

West-coast vs east-coast asymmetry at the same latitude: subtropical west coasts have Csa Mediterranean (cold offshore current, summer subsidence); east coasts have Cfa humid sub-tropical or Cwa monsoon (warm offshore current, year-round or summer rain). The mirror pair Rome (Csa) ↔ Shanghai (Cfa) ↔ Delhi (Cwa) shows this clearly.

9 · India in Köppen — 9 climate sub-types

India is uniquely educational — its 3.3 million km² spans the tropical, sub-tropical, arid, mountain and (in Ladakh) cold-desert/tundra fringe. Köppen and successors (Stamp 1932, Subrahmanyam, Mishra) identify 8–9 sub-types across the country.

Fig 11.4 — Schematic Köppen climate map of India. Aw (tropical savanna) dominates the peninsula; Cwa/Cwg blankets the N Ganga plain; Am hugs the Western Ghats & NE hills; BWhw sits in Thar; BShw fringes it; ET/BWk covers Ladakh; Dfc/Cwb takes the Himalayan slope. Andaman & Lakshadweep are Af. Tamil Nadu shows As (NE-monsoon dominance — rare global occurrence of "summer dry" in tropics).

Code	Region	Annual T	Annual P	Vegetation / land-use
Af	Andaman & Nicobar · Lakshadweep	26–28 °C	2 500–3 000 mm	Evergreen rainforest · coconut · spice
Am	W Ghats coastal strip · NE India (Meghalaya, Assam, AP, Nagaland)	22–26 °C	2 000–11 873 mm (Mawsynram)	Tropical evergreen / semi-evergreen · tea
Aw	Most of peninsular India south of Vindhyas	23–28 °C	750–1 500 mm	Tropical deciduous · cotton · jowar · bajra
As	Tamil Nadu coast (Chennai → Kanyakumari)	26–29 °C	900–1 200 mm (Oct-Dec)	Mixed deciduous · paddy · groundnut
BShw	Central Rajasthan · Saurashtra · Marathwada · Rayalaseema	25–28 °C	300–500 mm	Thorny scrub steppe · millets · pulses
BWhw	W Rajasthan (Thar) · Kutch	26–28 °C	< 250 mm	Xerophytes · sparse acacia · pastoral
Cwa / Cwg	N Ganga plain (Punjab, Haryana, Delhi, UP, Bihar W)	23–26 °C	600–1 100 mm	Tropical deciduous · wheat-rice · sugarcane
Cfa	E Ganga plain (parts of Bihar, W Bengal)	24–27 °C	1 200–1 800 mm	Sub-tropical moist · rice · jute
Dfc / Cwb	Himalayan mid-slopes (1 500–3 000 m)	5–18 °C	1 000–2 500 mm	Coniferous / mixed forest · apple · saffron
ET / BWk	Ladakh · upper Spiti · Kinnaur	< 0 to 5 °C	< 200 mm	Cold desert · barley · alpine pasture

Why India is a "Köppen lab": within 3 000 km north-south, India covers ten climate sub-types — equatorial rainforest, monsoon, savanna, hot desert, semi-arid steppe, humid sub-tropical, monsoon sub-tropical, alpine, and cold desert. UPSC often tests which Köppen code applies to a particular Indian station — memorise: Delhi Cwa/Cwg · Mumbai Aw (or Am margin) · Chennai As · Kolkata Aw/Am · Bengaluru Aw · Mawsynram Am · Jaisalmer BWhw · Leh BWk/ET.

10 · Climate change & shifting Köppen boundaries

Köppen boundaries are not fixed — they shift as long-term means of T and P change. Multiple recent studies (Beck et al. 2018; Cui et al. 2021; Chen & Chen 2013) show that under anthropogenic warming, climate zones are migrating poleward and upward at ~5–15 km/decade since 1950, and the rate is accelerating.

Key observed shifts (Köppen-Geiger updated 1901→2020)

Tropical climates (A) expanding poleward — Aw and Am zones moving into former Cwa areas of S China, S USA, N Australia.
Arid B zones expanding in subtropics (Sahel, Mediterranean fringe, Australia) due to Hadley cell expansion (~1° latitude per decade).
Mediterranean Csa shrinking — heat & declining winter rain push it toward semi-arid BSk.
Sub-arctic Dfc retreating as winters warm faster than summers; replaced by Dfb humid continental.
Tundra ET shrinking, ice-cap EF margins receding (Greenland, Antarctica peninsula).
India — Cwg margin pushing north into former Dfc Himalayan foothills; BWhw expanding south-east; mountain ET fringe in Ladakh contracting; Western Ghats Am may shift due to monsoon intensification/variability.

UPSC implications: static climate maps in older NCERT may not match current IPCC AR6 maps. Boundaries are moving targets. Mains questions increasingly ask about climate-change-driven biome shifts, agricultural-zone displacement, water-stress migration, and the policy response (NAPCC, state climate action plans, NDC commitments).

IPCC AR6 (2021) headline: "Each of the last four decades has been successively warmer than any decade that preceded it since 1850." Climate zones are migrating poleward and upslope; the agricultural calendar, water-stress hotspots, and vector-borne disease boundaries are all moving with them. Köppen classification is no longer purely descriptive — it is becoming a monitoring tool for climate-change impact assessment.

PYQs & Practice — Prelims and Mains kept separate

A · Prelims (MCQ) — UPSC past + practice

Direct UPSC CSE Prelims questions touching climate classification, climatic regions, Köppen letters, Mediterranean / equatorial / monsoon / tundra signatures, and India's climate types — followed by model practice MCQs.

UPSC CSE Prelims 2014

Q. The seasonal reversal of winds is the typical characteristic of —

(a) Equatorial climate · (b) Mediterranean climate · (c) Monsoon climate · (d) All of the above

Answer: (c) Monsoon climate (Köppen Am / Aw / Cwa).

UPSC CSE Prelims 2013

Q. Variations in the length of daytime and nighttime from season to season are due to —

(a) the earth's rotation on its axis · (b) the earth's revolution round the sun in an elliptical manner · (c) latitudinal position of the place · (d) revolution of the earth on a tilted axis

Answer: (d) Revolution on a tilted axis (23½°) — same reason latitudinal climate belts exist (Köppen's empirical zoning).

UPSC CSE Prelims 2012

Q. The Himalayan Range is very rich in species diversity. Which one among the following is the most appropriate reason?

(a) Heavy seasonal rainfall · (b) High mountains and valley flora · (c) Various climatic regimes due to altitude · (d) Confluence of different bio-geographical zones

Answer: (d). Linked to Trewartha's Group H highland climate — vertical zonation creates the diversity.

UPSC CSE Prelims 2011

Q. A geographic region has the following distinct characteristics: (1) Warm and dry climate (2) Mild and wet winter (3) Evergreen oak trees. The above features are the distinct characteristics of which one of the following regions?

(a) Mediterranean · (b) Eastern China · (c) Central Asia · (d) Atlantic coast of North America

Answer: (a) Mediterranean (Köppen Csa / Csb) — dry summer, wet mild winter, sclerophyll evergreen oak / olive / cork.

UPSC CSE Prelims 2013

Q. The most important factor in shaping the structure of a forest is —

(a) soil · (b) climate · (c) grazing · (d) aspect

Answer: (b) Climate (T & P regime — exactly what Köppen captures via vegetation as proxy).

UPSC CSE Prelims 2010

Q. A geographic region has the following characteristics: (1) Long winters with rain and snow (2) Short and mild summers (3) Annual precipitation distributed throughout the year (4) Coniferous forests. Which one of the following regions matches?

(a) Mediterranean · (b) Equatorial · (c) Steppe · (d) Taiga

Answer: (d) Taiga / Boreal (Köppen Dfc) — Siberian / Canadian boreal coniferous belt.

UPSC CSE Prelims 2017

Q. Which of the following leaf-modifications occur(s) in the desert areas to inhibit water loss?

Hard and waxy leaves
Tiny leaves or no leaves
Thorns instead of leaves

Select the correct answer:

(a) 1 only · (b) 2 & 3 · (c) 1 & 3 · (d) 1, 2 & 3

Answer: (d) All three. Xerophytic adaptations of Köppen BWh / BWk desert vegetation.

UPSC CSE Prelims 2010

Q. A geographic region has the following characteristics — Equatorial position, dense evergreen forests, high humidity, uniform high temperature throughout the year. The region most likely is —

(a) Mediterranean · (b) Equatorial (Köppen Af) · (c) Monsoon · (d) Savanna

Answer: (b) Equatorial / Tropical Rainforest — Köppen Af (Amazon, Congo, Indonesia).

Practice MCQs (model)

Practice

Q. Who is regarded as the father of modern climatology?
(a) Strahler · (b) Wladimir Köppen · (c) Thornthwaite · (d) Trewartha

Ans: (b) Wladimir Köppen — first comprehensive empirical scheme (1884, finalised 1936).

Practice

Q. In Köppen's classification, the letter "A" stands for —
(a) Arid · (b) Tropical humid · (c) Mild temperate · (d) Polar

Ans: (b) Tropical humid (mean T of coldest month ≥ 18 °C).

Practice

Q. The Köppen code Aw indicates —
(a) Tropical rainforest · (b) Tropical savanna with dry winter · (c) Tropical monsoon · (d) Tundra

Ans: (b) Tropical Savanna with dry winter — covers much of Deccan plateau.

Practice

Q. The "magic number" 18 °C in Köppen separates —
(a) A from C · (b) C from D · (c) D from E · (d) B from H

Ans: (a) A from C — coldest-month mean ≥ 18 °C = tropical (A).

Practice

Q. The threshold mean T of warmest month = 10 °C separates —
(a) A from C · (b) C from D · (c) D from E · (d) ET from EF

Ans: (c) D (continental) from E (polar) — also defines tree-line.

Practice

Q. The letter "B" in Köppen denotes —
(a) Boreal · (b) Arid / Dry · (c) Wet tropical · (d) Highland

Ans: (b) Dry (B) — determined by P-T threshold, not temperature alone.

Practice

Q. Köppen's BWh stands for —
(a) Cool desert · (b) Hot desert · (c) Steppe · (d) Tundra

Ans: (b) Hot desert (Thar, Sahara, Arabian) — W = wüste (desert), h = heiss (hot).

Practice

Q. The Mediterranean climate corresponds to Köppen code —
(a) Cwa · (b) Csa / Csb · (c) Cfb · (d) Dfa

Ans: (b) Csa / Csb — dry summer (s), mild winter rain.

Practice

Q. Tundra climate (Köppen ET) is defined by —
(a) all months > 10 °C · (b) warmest month between 0 °C and 10 °C · (c) all months < 0 °C · (d) coldest month < -38 °C

Ans: (b) Warmest month 0–10 °C — no trees, only mosses / lichens.

Practice

Q. Group H (highland) climate was added to Köppen by —
(a) Thornthwaite · (b) Trewartha · (c) Strahler · (d) Penck

Ans: (b) Glenn Trewartha (1968) — added for mountain belts (Himalayas, Andes, Rockies, Alps).

Practice

Q. Thornthwaite (1948) classified climates on the basis of —
(a) Mean temperature only · (b) P/E ratio & T/E ratio (Moisture Index) · (c) Wind patterns · (d) Cloud cover

Ans: (b) Precipitation-Evaporation & Thermal-Efficiency ratios (Moisture Index = 100 [P/PE – 1]).

Practice

Q. Most of peninsular India falls under Köppen's —
(a) Aw · (b) Cfa · (c) Dfb · (d) BSh

Ans: (a) Aw — Tropical Savanna with dry winter.

Practice

Q. The Indo-Gangetic plain is mostly Köppen —
(a) Aw · (b) Cwa / Cwg · (c) BSh · (d) Dfa

Ans: (b) Cwa (Cwg in Köppen's original India sub-types) — Humid Subtropical with dry winter, monsoonal Gangetic.

Practice

Q. Western Ghats windward slopes & NE India fall under Köppen —
(a) Af · (b) Am · (c) Aw · (d) Cfa

Ans: (b) Am — Tropical Monsoon (short dry, very heavy SW monsoon).

Practice

Q. Tamil Nadu coast — winter (NE) monsoon rainfall — Köppen code —
(a) Aw · (b) As · (c) Am · (d) Af

Ans: (b) As (tropical with dry summer) — rare globally, Coromandel coast is a classic example because of NE monsoon.

Practice

Q. Ladakh & Tibetan Plateau in Köppen scheme are —
(a) ET · (b) BWk · (c) EF · (d) Dfc

Ans: (b) BWk — Cold Desert (low precipitation in rain-shadow + cold).

Practice

Q. Andaman & Nicobar plus Lakshadweep fall under Köppen —
(a) Af · (b) Aw · (c) Cwa · (d) BSh

Ans: (a) Af — Tropical Rainforest (rain in every month, mean T > 18 °C all year).

Practice

Q. The Rajasthan-Thar core is classified Köppen —
(a) BSh · (b) BWh · (c) Aw · (d) Cfa

Ans: (b) BWh — Hot desert (annual P < 250 mm, T very high).

Practice

Q. Boreal coniferous forest (Taiga) corresponds to Köppen —
(a) Cfb · (b) Dfc · (c) ET · (d) BSk

Ans: (b) Dfc — Subarctic with cold short summer, snowy winter.

Practice

Q. The world's largest area under Köppen EF (ice-cap) is —
(a) Greenland · (b) Siberia · (c) Antarctica · (d) Arctic Ocean

Ans: (c) Antarctica — all months below 0 °C.

Practice

Q. Climate classifications that use vegetation as a proxy for climate are called —
(a) Genetic · (b) Applied · (c) Empirical · (d) Thermal

Ans: (c) Empirical (Köppen, Trewartha) — vs Genetic (Flohn — based on air-masses) and Applied (Thornthwaite — based on water balance).

Practice

Q. The 2007 update of Köppen by Peel, Finlayson & McMahon used —
(a) aerial photographs · (b) high-resolution global station data & GIS · (c) palaeoclimate proxies · (d) satellite cloud cover

Ans: (b) Peel-Finlayson-McMahon 2007 used global gridded climate data to refine Köppen-Geiger map (widely used today).

Practice

Q. "Climograph" plots —
(a) Pressure vs altitude · (b) Mean monthly T (line) & mean monthly P (bars) · (c) Wind speed vs direction · (d) Cloud cover vs sunshine

Ans: (b) Monthly T line + P bars — diagnostic visual for Köppen typing.

Practice

Q. Aristotle's 3-zone climate division was based on —
(a) Vegetation · (b) Sun-angle / latitude (Torrid · Temperate · Frigid) · (c) Air-mass · (d) Rainfall

Ans: (b) Latitude-based sun-angle zones (earliest known classification).

B · Mains (descriptive) — UPSC past + practice

GS Paper 1 (Physical Geography & Indian Geography) Mains questions on Köppen scheme, Indian climate types, Mediterranean / monsoon / equatorial regions, climate change & shifting boundaries — plus model practice questions with diagram cues.

UPSC CSE Mains 2014 · GS-1

Q. Bring out the causes for the formation of heat islands in the urban habitats of the world. (10 marks · 150 words)

Approach (climate-classification angle): Urban Heat Island creates a local micro-climate that can lift a city by half a Köppen sub-type (e.g. Delhi NCR effectively warmer than its Cwa surroundings). Causes: low albedo (asphalt, concrete), waste heat, low evapotranspiration, canyon geometry, aerosol blanket. Effects: lengthened summers, increased BWh-like dryness in interiors. Conclude with sponge-city / cool-roof responses.

UPSC CSE Mains 2017 · GS-1

Q. "In spite of adverse environmental impact, coal mining is still inevitable for development." Discuss. (15 marks · 250 words)

Climate hook: CO₂ from coal accelerates shift of Köppen boundaries — BWh expanding northward, Cwa pushing into Cfa, alpine Dfc shrinking. Tie to IPCC AR6: every 0.1 °C warming shifts climate belts ~15 km poleward / 150 m upward. Suggest just-transition, renewables, carbon capture.

UPSC CSE Mains 2019 · GS-1

Q. Discuss the causes of depletion of mangroves and explain their importance in maintaining coastal ecology. (10 marks · 150 words)

Diagram cue: Fig 11.4 (India Köppen). Climate link: Mangroves thrive in Köppen Am / Aw coasts with high precipitation + tidal regime (Sundarbans, Bhitarkanika, Pichavaram). Loss → coastal erosion, cyclone vulnerability rising as climate belts shift & AS cyclones intensify. Linkage to Trewartha highland-runoff systems feeding deltas.

UPSC CSE Mains 2021 · GS-1

Q. The process of desertification does not have climatic boundaries. Justify with examples. (10 marks · 150 words)

Approach: Köppen sets static climatic boundaries (BWh / BSh / Aw), but desertification spreads ACROSS them — Sahel (Aw → BSh shift), Aral (BSk-aggravated), Thar (BWh expanding into BSh Rajasthan), Mediterranean Spain (Csa → BSk land-degradation). Drivers: over-grazing, deforestation, irrigation salinity, CC. Hence climate-class lines are descriptive, not protective. UNCCD framework; India's Bonn Challenge commitment.

UPSC CSE Mains 2020 · GS-1

Q. How are the fjords formed? Why do they constitute some of the most picturesque areas of the world? (10 marks · 150 words)

Climate-class link: Fjord coasts (Norway, NZ South Is., Chile S., BC Canada) lie in Köppen Cfb / Cfc (Marine West-Coast) — moderated by westerlies & warm currents. Cite this as why fjord regions are mild despite high latitude — Köppen's empirical wisdom in action.

UPSC CSE Mains 2013 · GS-1

Q. Bring out the causes for more frequent occurrence of landslides in the Himalayas than in Western Ghats. (10 marks · 150 words)

Climate angle: Himalayas span Cwa → Dfc → ET → EF + Trewartha H highland — altitudinal climatic stress (freeze-thaw, monsoon torrents on steep neo-tectonic slopes) accelerates mass-wasting. Western Ghats stay in Am / Aw with mature regolith and gentler relief.

UPSC CSE Mains 2015 · GS-1

Q. Major hot deserts in the northern hemisphere are located between 20–30 degrees latitudes and on the western side of the continents. Why? (10 marks · 150 words)

Diagram cue: Fig 11.3 (world climate map). Approach: Köppen BWh belt aligns with subtropical high (descending limb of Hadley), cold offshore currents (Canary, California, Peru-Humboldt) suppressing convection, trade-wind divergence, rain-shadow of subtropical highs. Examples: Sahara, Arabian, Atacama, Namib, Kalahari, Sonoran. Conclude with shrinking of Hadley cell under CC pushing BWh poleward (Mediterranean drying).

Practice Mains Questions (model)

Practice

Q. Explain Köppen's empirical scheme of climate classification. Why is it the most widely used despite later refinements? (15 marks · 250 words)

Diagram cue: Fig 11.1 (decision tree) + 14-row type table. Approach: 5 main groups (A/B/C/D/E) + 2nd/3rd-letter logic. Strengths: vegetation-anchored, replicable from station data, global comparability, intuitive maps. Limits: ignores wind, air-masses (genetic), water balance (applied). Cover Peel et al. 2007 GIS update.

Practice

Q. Compare Köppen and Thornthwaite climate-classification systems. (10 marks · 150 words)

Diagram cue: 7-row comparison table (basis, key variables, approach, output classes, strength, weakness, use-case). Köppen = empirical / vegetation-based / 5 main + 11 types. Thornthwaite = applied / water-balance (P/E + T/E, Moisture Index) / 6 humidity classes. Köppen → broad-brush mapping; Thornthwaite → agronomy & hydrology. Both used in tandem today.

Practice

Q. Distinguish among empirical, genetic and applied classifications of climate. Cite one example of each. (10 marks)

Approach: Empirical (observable T-P data, vegetation proxy) — Köppen. Genetic (causative — air-masses, fronts, atmospheric circulation) — Flohn 1950. Applied (purpose-specific, water balance, agro-climatic) — Thornthwaite. Note Strahler (1969) attempted hybrid.

Practice

Q. Why did Trewartha modify Köppen's classification? What is the relevance of his "Group H" for India? (10 marks)

Approach: Köppen lumped highlands into surrounding lowland category — masking altitudinal zonation. Trewartha (1968) added H (highland) where altitude overrides latitude. India relevance: Himalayas, Karakoram, Hindu Kush, Nilgiri high all fit H — host distinct vegetation belts (sal → oak → deodar → birch → alpine meadow → tundra → permafrost) within tens of km. Critical for forest policy, hydro-projects, tourism climatology.

Practice

Q. Describe the major climatic types of India based on Köppen's scheme, with a sketch map. (15 marks)

Diagram cue: Fig 11.4 (India Köppen map — Aw, Am, As, Af, BWh, BSh, BWk, Cwa/Cwg, Cfa, Dfc, ET). Approach: 10-row India table — region, code, T-P signature, vegetation, mnemonic "WACS" (W. Ghats, Andaman, Coromandel, Sundarbans). Highlight unusual As (Tamil Nadu, NE monsoon) — rare globally.

Practice

Q. "Köppen's classification is essentially a vegetation classification dressed up as climate." Critically examine. (15 marks)

Approach: Köppen used vegetation (de Candolle's botanic zones) as proxy → criticism: tautological, lags climate change, ignores soils & wind. Defence: vegetation INTEGRATES T+P over years (best natural sensor); cheap to map; aligned with biome science. Conclude as a balance — flawed but functional.

Practice

Q. Climate change is shifting Köppen boundaries worldwide. Discuss with Indian and global examples. (15 marks)

Diagram cue: Fig 11.3 + Fig 11.4. Approach: IPCC AR6: 1.1 °C warming since 1850 → boundaries shifted ~15 km poleward per decade. Global: Mediterranean (Csa) drying toward BSk; Arctic ET → Dfc; alpine EF → ET. India: BWh expansion into Rajasthan BSh; Western Ghats Am erosion; Himalayan EF/ET retreat. Implications — agriculture, biodiversity, water security, migration. Way forward: dynamic agro-climatic re-zoning (ICAR), revised crop-planning.

Practice

Q. "Tropical Monsoon climate (Am) is unique to South & Southeast Asia." Examine. (10 marks)

Approach: Am defined by short dry winter + heavy concentrated SW monsoon. Found in West Coast India, Bangladesh-Myanmar, Indo-China, parts of Philippines, also Guinea coast & small parts of N. Australia. Driver: differential heating Asia-Indian Ocean, Himalayan barrier, ITCZ migration. Conclude with NE-monsoon corollary (Tamil Nadu = As).

Practice

Q. Read a climograph and identify Köppen type. Why is the climograph the diagnostic tool for empirical classification? (10 marks)

Diagram cue: Fig 11.2 (5-station climograph panel — Singapore, Bengaluru, Rome, Delhi, Verkhoyansk). Approach: Decoding rules — coldest-month T → A/C/D/E, warmest-month T → D/E, P-pattern → f/m/w/s, P-T threshold → B test. Train aspirants to read 12-bar P + T-line and assign codes in 60 s. Conclude — climograph reduces vast data to one glance.

Practice

Q. Why do Mediterranean & Monsoon climates lie on opposite ends of the dry-season axis though both occur in similar latitudes? (10 marks)

Approach: Both lie 20°–40°, but Mediterranean (Csa) — dry summer (subtropical high overhead), wet mild winter (westerlies-Polar Front cyclones). Monsoon (Am / Aw) — wet summer (ITCZ overhead + land-sea contrast), dry winter (high pressure overhead). Driver — annual oscillation of subtropical high vs ITCZ, plus continental size (Asia = massive monsoon engine; Mediterranean basin = small + Atlantic westerlies dominate). Mirror-image rainfall pattern in same latitudes.

Practice

Q. Examine the relevance of Thornthwaite's Moisture Index for agro-climatic planning in India. (10 marks)

Approach: MI = 100 [P/PE – 1]. MI > 100 → perhumid (Western Ghats, NE); 0–100 → humid / sub-humid (Gangetic plain); -33 to 0 → semi-arid (Deccan); < -33 → arid (Rajasthan). ICAR uses these for crop zoning (rice in MI > 0, millets in MI -20 to 0, oilseeds in MI -33 to -20). Updates under CC needed — MI shifting negative in many districts.

Practice

Q. Explain why Tamil Nadu coast is classified as Köppen As (tropical dry-summer) — a globally rare type. (10 marks)

Approach: Tamil Nadu's main rainy season is Oct–Dec NE monsoon (winter for NH); summers (Apr–Aug) are dry due to offshore SW monsoon & rain-shadow of Western Ghats. Inverts the typical tropical pattern — hence As. Globally rare because most tropical regions have summer rain. Implications — paddy calendar, Cauvery dispute, reservoir management.

Practice

Q. "The world climate map is essentially the world vegetation map." Discuss. (10 marks)

Approach: Köppen drew on de Candolle's botanic zones; vegetation = integrator of climate. Tropical rainforest = Af; savanna = Aw; Mediterranean sclerophyll = Csa; steppe = BSk; taiga = Dfc; tundra = ET; ice-cap = EF. One-to-one mapping. Conclude — vegetation as climate's signature.

Revision — 15 Memory-Anchor Facts

3 approaches to climate classification: Empirical (Köppen, Trewartha — vegetation/data proxies), Genetic (Flohn — air-masses), Applied (Thornthwaite — water balance).
Aristotle's 3 zones (Torrid / Temperate / Frigid) — earliest known climate scheme, based on sun-angle / latitude.
Köppen (1884, finalised 1936) = father of modern climatology. Empirical scheme using mean monthly T & P with vegetation proxies (de Candolle).
Köppen 5 main groups: A Tropical (coldest-month T ≥ 18 °C) · B Dry (P below P-T threshold) · C Mild temperate (coldest -3 to 18 °C) · D Continental (coldest < -3, warmest ≥ 10) · E Polar (warmest < 10).
Magic numbers: 18 °C separates A / C · 10 °C separates D / E (= tree-line) · -3 °C separates C / D · 0 °C inside E separates ET (tundra) / EF (ice-cap).
2nd-letter (precipitation): f = no dry season (German feucht) · m = monsoon · w = dry winter · s = dry summer · W = desert (wüste) · S = steppe · T = tundra · F = frost (ice-cap).
3rd-letter (temperature): a = hot summer ≥ 22 °C · b = warm < 22 · c = cool short summer · d = very cold winter < -38 · h = hot (B group ≥ 18 mean annual) · k = cold (B group < 18) · g = Ganges-type (Köppen India sub-code, summer peak before monsoon).
11 Köppen types (with India's typical zones): Af (Andaman, Lakshadweep) · Am (W. Ghats, NE India) · Aw (Deccan core) · As (Tamil Nadu coast — globally rare) · BWh (Thar) · BSh (Rajasthan steppe) · BWk (Ladakh cold desert) · Cwa/Cwg (Indo-Gangetic plain) · Cfa (E. Ganga) · Dfc (Himalayan slope, Sikkim high) · ET (Ladakh high alpine).
Trewartha (1968) modified Köppen by adding Group H (highland) for mountain belts & refining the C-group. Critical for Himalayan zonation in India.
Thornthwaite (1948) built an applied climate system on water balance: P/E ratio (precipitation-evaporation), T/E ratio (thermal efficiency), & Moisture Index MI = 100 [P/PE – 1]. 6 humidity classes: A perhumid (MI > 100) · B humid · C sub-humid · D semi-arid · E arid · with thermal sub-categories.
Genetic (Flohn 1950) classification uses planetary wind belts & air-masses — Equatorial westerlies, Trade-winds, Subtropical highs, Mid-lat westerlies, Polar easterlies, Polar high — yielding 7 climatic zones.
Peel-Finlayson-McMahon (2007) refined Köppen-Geiger map using global high-resolution gridded climate data → "Köppen-Geiger 2007" is the most cited modern world climate map.
Climograph = mean monthly T (line) + mean monthly P (bars). Read coldest-month T (→ A/C/D/E), warmest-month T (→ D/E split), P-pattern (→ f/m/w/s), P-T threshold (→ B test). Used to assign Köppen code at a glance.
India in Köppen — WACS mnemonic for unusual / boundary types: Western Ghats Am · Andaman+Lakshadweep Af · Coromandel (Tamil Nadu) As · Sundarbans (Aw with tropical mangrove). Add core types Aw (Deccan), BWh (Thar), Cwa/Cwg (Gangetic plain), BWk + ET (Ladakh), Dfc (Sikkim high).
Climate change & shifting boundaries (IPCC AR6): 1.1 °C warming since 1850 — Köppen boundaries shifting ~15 km poleward / 150 m upward per decade. BWh expanding (Thar, Sahel); Mediterranean Csa drying toward BSk; alpine EF → ET; Himalayan ET → Dfc; Arctic ET → Dfc (greening Arctic). Demands dynamic agro-climatic re-zoning & revised crop-planning.

Mini-reference

Climate30-yr avg of weather (WMO)
Köppen 1918vegetation-based world scheme
5 main groupsA · B · C · D · E (+ H by Trewartha)
A — Tropicalcoldest month ≥ 18 °C
B — Dryevap > precip (arid/semi-arid)
C — Warm temperatecoldest 18 to –3 °C
D — Cold continentalcoldest < –3 °C; warmest > 10 °C
E — Polarwarmest < 10 °C
H — Highland(Trewartha) mountain climates
Aftropical rainforest (no dry month)
Amtropical monsoon (short dry)
Awtropical savanna (winter dry)
BWh / BWkhot / cold desert
BSh / BSkhot / cold steppe
Cfahumid sub-tropical (Gangetic plain east)
Cfbmarine west-coast (NW Europe)
Cs / CsaMediterranean (dry summer)
Cwgmonsoon w/ dry winter (N India)
Dfa / Dfbhumid continental
Dfcsub-arctic taiga
ETtundra (warmest 0–10 °C)
EFice-cap (warmest < 0 °C)
Second letterf wet · w winter-dry · s summer-dry · m monsoon
Third lettera hot summer · b warm · c cool · d very cold · h hot · k cold
Trewartha 1968added group H, simplified codes
Thornthwaite 1948P/E moisture + T/E thermal index
PE indexmoisture availability
TE indexthermal efficiency
Climographmonthly T (line) + P (bar) graph
Equatorial AfAmazon, Congo, Indonesia
SahelBSh tropical steppe
SaharaBWh hot desert
MediterraneanCsa — basin + Calif + Chile + S Afr + SW Aus
Marine WCCfb — NW Eur, BC, S Chile, NZ, Tasmania
Taiga (boreal)Dfc / Dwc — Russia, Canada, Scandinavia
TundraET — Arctic fringe, Iceland coast
Ice-capEF — Antarctica, Greenland interior
India dominantAw (peninsula) + Cwg (N plain) + BWhw (Thar)
LadakhBWkw cold desert / ET margin
MawsynramAm tropical monsoon
KeralaAm with short dry

Keyword cloud

KöppenTrewarthaThornthwaiteClimographAwAmAfBWhBShBWkBSkCfaCfbCsaCwgDfaDfbDfcDwcETEFH highlandTropicalSavannaMonsoonMediterraneanSteppeDesertHumid sub-tropicalMarine west coastContinentalTaigaTundraIce-capVegetation beltP/E ratioT/E ratioWladimir KöppenGlenn TrewarthaPenckSupanAristotle zonesBoundary shiftClimate changeIPCC AR6India climateMawsynramTharLadakhKeralaSaharaAmazonCongoTundraAntarcticaGreenlandSahelNW EuropePacific NWTropic of CancerTropic of CapricornArctic CircleAntarctic CircleUPSC GS-1

Self-check (10 Qs)

Which Köppen group has coldest month T ≥ 18 °C?
What does the letter f mean in Cfb?
Mediterranean climate has which letters?
Which two letters denote India's Gangetic plain in Köppen?
Thar Desert in Köppen — code?
Trewartha added which new group?
What is P/E ratio of Thornthwaite?
Which climate has the largest annual T range?
Where is Cfb climate found (give 2 examples)?
Why is Köppen criticised?

World Climate Classification — Köppen · Trewartha · Thornthwaite

Why this topic matters for UPSC

Contents

1 · Why classify climates · criteria

Purpose of climate classification

2 · Early classifiers — from Aristotle to Supan

Greek 3-zone scheme (Aristotle, ~350 BCE)

3 · Köppen system — 5 main groups + letter codes

The 5 main groups (capital letter)

4 · The 11 Köppen climate types in detail

5 · Trewartha modification (1968)

Trewartha's main changes

6 · Thornthwaite system — P/E ratio (1948)

The two key indices

Köppen vs Thornthwaite — comparison

7 · Reading a climograph

How to read a climograph in 4 steps

8 · World distribution of climates

9 · India in Köppen — 9 climate sub-types

10 · Climate change & shifting Köppen boundaries

Key observed shifts (Köppen-Geiger updated 1901→2020)

PYQs & Practice — Prelims and Mains kept separate

A · Prelims (MCQ) — UPSC past + practice

Practice MCQs (model)

B · Mains (descriptive) — UPSC past + practice

Practice Mains Questions (model)

Revision — 15 Memory-Anchor Facts