Factors of India's climate: location and relief

Detail

1. The six factors at a glance

• Factors determining India's climate are the things that decide how hot, cold, wet or dry a place in India is. NCERT (Class 11) puts them in two groups:
• Location and relief: latitude, the Himalayan mountains, the distribution of land and water, distance from the sea, altitude and relief.

• Air pressure and winds: surface winds, upper-air currents such as jet streams (narrow belts of very fast wind high in the atmosphere), western disturbances, cyclones, and links with the oceans. These are covered in later sections.

• Climate is the average weather of a large area over a long period, about 30 years. Weather is the state of the air at one place and time.

• Daily (diurnal) range is the gap between the day's highest and lowest temperature. Annual range is the gap between the warmest and coldest month.

Factor	What it controls	Indian example
Latitude	How much sun heat a place gets	Kanniyakumari warm all year, Srinagar cool
Himalayas	Keep cold air out and monsoon rain in	North India escapes Central Asian winters
Land and water distribution	Seasonal pressure and the reversal of winds	Monsoon winds blow onto land in summer and off it in winter
Distance from the sea	Equable vs extreme climate	Mumbai range about 14°C, Nagpur about 34°C
Altitude	Temperature falls with height	Darjiling 4°C vs Agra 16°C in January
Relief	Where rain falls and where it does not	Western Ghats wet, Deccan dry

2. Latitude

• Latitude is a place's distance north or south of the Equator, measured in degrees.
• The Tropic of Cancer (23°30′N) runs through the middle of India, from Gujarat in the west to Mizoram in the east. It crosses 8 states: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura and Mizoram.
• South of the Tropic, the climate is tropical:
• The area is close to the Equator, so the sun stays high in the sky all year.
• Temperatures stay high, and the daily and yearly ranges are small.

• Examples: Kanniyakumari (about 8°N, Tamil Nadu) and the Nicobar Islands are warm all year.

• North of the Tropic, the climate is sub-tropical and temperate:

• The area is far from the Equator, so the sun's angle changes a lot between summer and winter.
• The climate is extreme, with large daily and yearly ranges.

• Example: Srinagar (about 34°N, Jammu and Kashmir) has cool summers and freezing winters.

• Why latitude matters (Class 7):

• Sun angle: near the Equator, the sun's rays fall almost straight down. The same heat is packed into a small area, so the ground gets hot.

• Path through the air: at high latitudes the rays come in at a slant. They pass through a thicker layer of air and spread over a larger area, so less heat reaches each spot.

• Exam point: half of India lies north of the Tropic, but the whole country is treated as a tropical monsoon land. This is because the Himalayas shut out cold air and the monsoon system covers the whole country.

3. The Himalayas as a climatic divide

• Himalayas as a climatic divide means the range splits two climates: the warm, wet Indian subcontinent to the south and the cold, dry Tibetan Plateau and Central Asia to the north.
• The range runs about 2,400 km from the Indus in the west to the Brahmaputra in the east. Many of its peaks are over 6,000 m high.
• Role 1: a wall against cold air in winter
• Very cold air builds up over Siberia and Central Asia in winter.
• The high mountain wall stops most of this Arctic and Central Asian air from flowing south.

• Result: north India has mild winters for its latitude. Delhi (about 28°N) is far warmer in January than places at the same latitude in Central Asia or interior China.

• Role 2: a trap for monsoon rain in summer

• The south-west monsoon winds carry moisture from the Indian Ocean.
• The mountains stop them and push them up, so they drop their moisture inside the subcontinent.

• Result: heavy rain falls over the Ganga plains and the north-east, while Tibet stays dry.

• Beyond NCERT: India without the Himalayas

• North India would have Central Asian winters, with long spells of freezing cold.

• The monsoon would spill north into Tibet, and the plains would get much less rain.

• Modern research: a wall more than a heater

• The classical view is that strong summer heating of the Tibetan Plateau drives the monsoon.
• Climate model studies find that monsoon strength depends more on heating of the low plains of north India than on heating of the high mountain slopes [3].
• This supports the idea that the mountains work mainly as a thermal insulator: a wall that keeps the cold, dry air of the higher latitudes away from the warm, moist monsoon air [3].

4. Distribution of land and water

• India's setting: the Indian Ocean surrounds the peninsula on three sides (the Arabian Sea in the west, the Bay of Bengal in the east and the Indian Ocean in the south). A high, continuous mountain wall lies to the north.
• Differential heating of land and water means that land heats up and cools down faster than water.
• Water lets sunlight pass deep inside it. It also mixes and moves, and it needs more heat to warm up.

• Land soaks up heat only in a thin top layer and gives it back quickly.

• Summer chain:

• Land heats faster than the sea.
• Air over the hot land rises, and a low (an area of low air pressure) forms over north-west India.
• A high (an area of high air pressure) sits over the cooler Indian Ocean.

• Wind blows from high to low, so moist south-west winds are drawn in from the sea. This brings monsoon rain.

• Winter chain:

• The land cools faster than the sea.
• A high forms over the land, especially north of the Himalayas, and a low forms over the warmer ocean.

• Dry, cool winds blow from land to sea, mainly from the north-east.

• Result: the winds reverse their direction with the season. This is the core meaning of monsoon (from the Arabic word mausim, meaning season).

• Theory link: this is the classical thermal theory, first set out by Edmond Halley (1686). Later explanations add the shift of the ITCZ (Inter Tropical Convergence Zone: the low-pressure belt near the equator where the trade winds of the two hemispheres meet), jet streams, and ocean links such as El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). These are covered in Section 4.

5. Distance from the sea

• Equable (maritime) climate: mild temperatures with a small gap between summer and winter. The sea calms down temperature swings, and land and sea breezes bring relief every day.
• Extreme (continental) climate: very hot summers, cold winters and a large range. These areas are far from the sea's influence.

Place	Location	Type	Annual range
Mumbai	West coast, Maharashtra (about 19°N)	Equable	About 14°C (NCERT, Class 7)
Nagpur	Centre of the Deccan, Maharashtra (about 21°N)	Extreme	About 34°C (NCERT, Class 7)

• Class 11 examples:
• Mumbai and the Konkan coast hardly know what extreme temperatures are.

• Inland places such as Delhi, Kanpur and Amritsar have extreme seasonal contrasts.

• Trap: Mumbai and Nagpur are at almost the same latitude. The difference comes from distance from the sea, not latitude.

6. Altitude

• Altitude is height above sea level. Temperature falls as you go up, by about 6.5°C for every 1,000 m. This is called the normal lapse rate.
• Air higher up is thinner. It holds less heat and is farther from the warm ground that heats it.

Pair	State	Same latitude?	Temperature
Agra (plains) vs Darjiling (about 2,000 m)	Uttar Pradesh vs West Bengal	Yes, both about 27°N	January: Agra 16°C, Darjiling 4°C
Coimbatore (plain) vs Ooty (Nilgiri Hills, about 2,240 m)	Both in Tamil Nadu	Close	Coimbatore 25-38°C; Ooty 10-25°C

• Hill stations grew up because of altitude. Examples run from Munnar (Kerala, Western Ghats) in the south to Tawang (Arunachal Pradesh, Eastern Himalaya) in the north-east. Shimla, Mussoorie and Ooty developed as summer retreats in colonial times.

7. Relief

• Relief is the shape of the land: mountains, plateaus, plains and valleys. It decides where rain falls.
• Orographic (relief) rain:
• Moist wind hits a mountain and is pushed up.
• The rising air cools, its water vapour condenses, and it rains on the side facing the wind (the windward side).

• The air that crosses the mountain and sinks on the other side (the leeward side) is dry and warms up. This dry belt is the rain-shadow area.

• Indian cases (June-September):

• Windward and wet: the western slopes of the Western Ghats (Konkan, Malabar coast) and Assam and the hills of the north-east.

• Leeward and dry: the southern plateau (Deccan), east of the Ghats, which lies in the rain shadow. Mumbai on the coast gets far more rain than Pune just across the Ghats.

• Relief also guides winds. The Arakan Yoma and the Meghalaya hills turn the Bay of Bengal branch westward up the Ganga valley. This is covered in Section 8.

8. Winds as a factor (Class 7)

• Hot, dry westerlies cause heat waves in Punjab, Haryana, Rajasthan and Madhya Pradesh in May and June. A heat wave is a spell of unusually high temperature that harms people and animals.
• Cold winds from beyond the Himalayas cause cold waves in the northern plains in winter.
• IMD heat-wave definition: the India Meteorological Department uses only maximum temperature. It declares a heat wave when a station's maximum reaches at least 40°C in the plains, 37°C at coastal stations or 30°C in hilly regions [2].
• The criteria must be met at 2 or more stations in a meteorological sub-division for at least 2 days in a row [2].

• A station whose normal maximum is 45°C or more can be declared under a heat wave for 2 or more days on the actual temperature alone [2].

• IMD cold-wave scale: for stations whose normal minimum is 10°C or more, a fall of 5-6°C below normal is a moderate cold wave. A fall of 7°C or more is a severe cold wave [2].

• IMD records daily maximum and minimum temperatures at about 550 surface observatories across India [2].
• The different-sounding figures above are the thresholds of different IMD tables: one absolute and one based on departure from normal. In MCQs, read which table the question uses.

9. Microclimate

• Microclimate is the special climate of a small area that is different from the climate of the region around it.
• Examples (Class 7):
• Enclosed valleys: cold air sinks into them at night, so they can be colder than nearby slopes.
• Forests: they are cooler and more humid than open land nearby.
• Urban heat island: a city is warmer than the countryside around it. Concrete and asphalt store heat, vehicles and air conditioners give out heat, and there are few trees. Delhi, Mumbai and Bengaluru show this effect.

Prelims Hooks

• The Tropic of Cancer passes through 8 states, from Gujarat in the west to Mizoram in the east. It does not pass through Odisha, Bihar or Uttar Pradesh.
• Mumbai (annual range about 14°C) vs Nagpur (about 34°C): both are near 19-21°N, so the difference comes from distance from the sea, not latitude.
• Agra (16°C) vs Darjiling (4°C) in January, both at about 27°N: the difference comes from altitude.
• Ooty (10-25°C) vs Coimbatore (25-38°C): both are in Tamil Nadu. Ooty is in the Nilgiri Hills.
• The Himalayas keep out cold Arctic and Central Asian winds and trap the south-west monsoon. Model studies show they act mainly as a thermal insulator, not a heat source [3].
• The thermal (differential heating) theory of the monsoon was given by Edmond Halley in 1686.
• Rain shadow: the Deccan plateau lies leeward of the Western Ghats. The windward slopes are the Konkan and Malabar coast.
• IMD heat wave thresholds: 40°C in the plains, 37°C on the coast and 30°C in the hills. The rule must be met at 2 or more stations for 2 days in a row [2].
• Microclimate examples: urban heat island, enclosed valley, forest. Trap: a heat wave is a regional wind effect, not a microclimate.

Mains Points

• Why India is a "tropical monsoon" country despite half of it lying north of the Tropic: the Himalayan wall blocks Central Asian cold air, and land-sea heating differences control the whole country. Latitude alone would make the north temperate (GS-I, distribution of key climate features).
• Relief and distance from the sea shape regional contrasts: the wet windward Ghats and the north-east are set against the dry Deccan rain shadow and extreme interior plains. These contrasts explain drought-prone Marathwada and Rayalaseema, cropping patterns, and why hill stations and coastal cities developed (GS-I).
• Factors behind disasters: hot westerlies over Punjab-Rajasthan-MP and cold Himalayan air over the northern plains bring heat waves and cold waves. IMD uses fixed thresholds (40/37/30°C) to issue warnings, and these feed state heat action plans. Urban heat islands make city heat worse, so green cover and cool roofs are used as responses (GS-III, disaster management) [2].
• Updating the classical theory: Halley's land-sea heating model is now combined with the Himalaya-as-insulator idea [3], ITCZ shift, jet streams and ENSO/IOD. An answer should show that India's climate comes from both location and relief and circulation.