Climate of India | ICSE Class 10 Geography Notes

Climate of India: regional temperature and rainfall contrasts, climatic controls, pressure and winds, monsoon mechanisms, jet streams and El Niño, summer weather, southwest monsoon branches, relief rainfall, retreating monsoon, winter rain, climate maps and interpretation of temperature and rainfall data.

What makes India’s climate monsoonal yet regionally varied?

How do weather and climate differ?

Weather is the momentary state of the atmosphere. Climate describes average weather conditions over a longer period. Temperature, air pressure, wind direction and speed, humidity and precipitation help describe both, but their timescales differ.

Weather can change within a day or a week. A hot afternoon followed by a thunderstorm is a weather change. Climate concerns the longer-term pattern, including the usual sequence of hot, rainy and cooler conditions.

Definition: A monsoon involves a seasonal reversal in wind direction. India has a hot monsoonal climate, with substantial regional differences within this broad seasonal pattern.

Monsoonal unity does not mean identical temperatures or equal rainfall everywhere. Kerala and Tamil Nadu differ from Uttar Pradesh and Bihar, while all belong to the broad monsoon climatic system. The timing of rainfall is as important as its amount.

Which contrasts show this diversity?

Most of India receives its main rainfall during June to September. Coastal Tamil Nadu receives important rainfall towards the beginning of winter. The Himalayas receive snowfall, while rain is the characteristic form of precipitation over most other parts of the country.

The symbol °C means degrees Celsius, a unit of temperature. In the following examples, the day or season matters: these are illustrative contrasts, not temperatures that remain fixed throughout the year.

Daily range means the difference between the highest and lowest temperatures within a day. It may be hardly seven or eight degrees Celsius in Kerala and the Andaman Islands, whereas the Thar Desert can experience much larger day-to-night changes.

How do latitude, altitude, the sea and the Himalayas control climate?

Why does location matter?

Latitude helps determine the heating received from the Sun. The Tropic of Cancer crosses central India. The southern part lies in the tropical zone, while the northern part extends into subtropical and temperate latitudes. Southern areas generally have smaller temperature ranges.

Altitude is height above mean sea level. Temperature generally decreases with height, making mountains cooler than nearby plains. Agra and Darjiling provide a useful comparison because they lie at approximately the same latitude but have different elevations.

The January temperature example is 16°C for Agra and 4°C for Darjiling. Latitude alone therefore cannot explain the contrast. The higher location of Darjiling helps explain its lower temperature. Several climatic controls act together at any one place.

Distance from the sea affects the strength of seasonal temperature contrasts. Water heats and cools more slowly than land. Coastal locations experience the sea’s moderating influence, while inland locations are less affected by it.

Mumbai and the Konkan coast have relatively equable conditions. Delhi, Kanpur and Amritsar experience stronger seasonal contrasts. Equable climate means relatively small temperature fluctuations; it does not mean that the weather never changes or that rainfall is evenly distributed.

How do mountains change winds and rain?

The Himalayas form a major climatic barrier. They protect the subcontinent from cold northern winds and obstruct moisture-bearing monsoon winds, encouraging rainfall within the subcontinent. Their influence extends beyond the temperature of the mountain region itself.

Relief, the arrangement of landforms, also affects wind direction, speed and rainfall distribution. The Western Ghats force moist air to rise on their western slopes. Areas to their east receive much less rain because they lie on the sheltered side.

Note: Do not use one factor to explain every climatic difference. Coastal moderation explains Mumbai’s smaller temperature contrasts, altitude helps explain Darjiling’s coolness, and relief helps explain rainfall differences across the Western Ghats.

How do pressure changes produce the southwest monsoon?

What sets air in motion?

Wind is air in motion. Pressure differences set it moving from higher towards lower pressure, while Earth’s rotation and friction affect its path. A pressure gradient is the change in pressure across a distance.

Land heats more quickly than the surrounding ocean during the hot season. Strong heating over the northern landmass helps establish low pressure, especially in northwestern India. The ocean to the south has relatively higher pressure because it warms more slowly.

The Inter Tropical Convergence Zone (ITCZ) is a low-pressure belt where trade winds meet and air tends to rise. Its seasonal movement is important to the monsoon. Over the Gangetic plain in summer, it is associated with the monsoon trough.

What is the sequence of the seasonal reversal?

1. Summer heating intensifies low pressure over the northwestern part of the subcontinent, while pressure over the ocean to the south remains relatively higher.
2. The ITCZ shifts northwards. Its position over northern India helps organise the low-pressure monsoon trough and the associated wind circulation.
3. Southeast trade winds from the Southern Hemisphere cross the equator towards the low-pressure region and acquire abundant moisture over the ocean.
4. Earth’s rotation deflects the moving air to its right in the Northern Hemisphere. These winds consequently approach India as the southwest monsoon.
5. The winds enter through the Arabian Sea and Bay of Bengal branches. Relief and the pressure pattern modify their routes across the country.

The Coriolis force describes the effect of Earth’s rotation on moving air. It explains why cross-equatorial winds do not simply continue along an unchanged straight path. The name “southwest monsoon” refers to the direction from which these winds generally arrive.

The seasonal reversal is more than an enlarged local sea breeze. Differential heating is important, but the shifting convergence zone, upper-air circulation and conditions over the oceans also contribute. No single explanation accounts fully for every feature of the Indian monsoon.

How do jet streams and El Niño influence the monsoon?

What role does upper-air circulation play?

Jet streams are narrow bands of fast-moving winds high in the atmosphere. Surface winds alone do not explain the seasonal circulation. Changes in the position of upper-air winds are associated with the arrival and behaviour of the monsoon.

The withdrawal of the westerly jet stream from its position south of the Himalayas over the northern plains is associated with the northward shift of the ITCZ. An easterly jet stream subsequently develops, and is linked with the burst of the monsoon.

The labels westerly and easterly describe the direction from which the winds blow. They refer here to upper-air currents, so they should not be confused with the moisture-bearing southwest winds nearer the surface.

In winter, the westerly upper-air circulation is relevant to the movement of the depressions that reach northwestern India. These disturbances bring some winter rain to the plains and snowfall to the Himalayas. This is a different rainfall setting from summer monsoon flow.

Why is El Niño relevant to India?

El Niño involves oceanic and atmospheric changes associated with unusually warm water off Peru in the eastern Pacific. It can disturb equatorial atmospheric circulation and influence weather far beyond the Pacific coast, including the Indian monsoon.

El Niño is used in long-range monsoon forecasting. Its influence belongs to a wider system: the monsoon is affected by several interacting conditions, so an El Niño reference should not be turned into a claim that every Indian region must experience an identical outcome.

One historical example is the 1990 to 1991 El Niño event, when southwest monsoon onset was delayed over most parts of India by five to twelve days. This illustrates a possible effect on timing, rather than a fixed delay for every event.

Note: Distinguish the mechanism from its influences. Seasonal pressure changes and cross-equatorial winds explain the basic reversal; jet streams and Pacific ocean-atmosphere changes help explain further features and variability.

What are the main features of the hot weather season?

How do temperature and pressure change?

With the apparent northward movement of the Sun, temperatures begin rising in northern India from March. April, May and June form the main summer period there. Strong heating is accompanied by falling pressure over the northern half of the country.

The zone of greatest heat shifts northwards as the season progresses. In March, a highest daytime temperature of about 38°C occurs in the Deccan Plateau. In April, temperatures of 38°C to 43°C occur in Gujarat and Madhya Pradesh.

By May, temperatures around 48°C are not uncommon in northwestern India. Southern India generally experiences less intense summer heat because of its peninsular position and oceanic influence. The higher parts of the Western Ghats remain cooler because of altitude.

The growing thermal low, a low-pressure area associated with intense heating, helps prepare the summer circulation. This should be connected with the subsequent arrival of moisture-bearing winds rather than treated as a separate, unrelated summer fact.

Which local winds and storms are important?

Kalbaisakhi is the local name associated with the destructive character of these storms in Bengal. In Assam they are called Bardoisila. The same storms may be damaging because of their violence yet beneficial because they supply moisture for crops.

Dust storms are common in May in Punjab, Haryana, eastern Rajasthan and Uttar Pradesh. They may bring temporary relief through light rain and a cooler breeze. The loo, however, is a hot, dry wind, not a rain-bearing thunderstorm.

How does the southwest monsoon advance through its two branches?

What is meant by the burst of the monsoon?

The arrival of moisture-laden winds can produce an abrupt beginning of rain, accompanied by thunder and lightning. This sudden onset is called the burst of the monsoon. Temperatures fall as the rainy season becomes established.

The southwest monsoon normally reaches the Kerala coast around 1 June. It advances towards Mumbai and Kolkata during June and spreads over the subcontinent by about mid-July. These are normal seasonal timings, not guaranteed arrival dates in every year.

Curved lines labelled with dates cross an outline map of India. Early June lines occur near the southern peninsula and the northeast; later June and July lines extend across central, northern and northwestern India.

Where do the branches carry moisture?

The Arabian Sea branch meets the Western Ghats, bringing heavy rain to their windward slopes and the western coastal plain. Another part enters north of Mumbai and travels along the Narmada and Tapi valleys into central India.

A further part reaches Saurashtra and Kachchh, then passes over western Rajasthan and along the Aravalis with scanty rainfall. Farther north, Arabian Sea winds meet the Bay of Bengal branch. Their combined influence brings rain to the western Himalayas.

The Bay of Bengal branch is redirected towards the subcontinent by the Arakan Hills along Myanmar’s coast. It enters West Bengal and Bangladesh from the south and southeast rather than retaining a southwest direction everywhere.

One part travels westwards along the Ganga plains towards Punjab. Another moves along the Brahmaputra valley, while a sub-branch encounters the Garo and Khasi hills. These routes help explain why the northeast receives such abundant rainfall.

Wind direction at a particular place therefore reflects both the broad monsoon circulation and local or regional influences. A monsoon map should show routes and direction changes, rather than identical southwest-pointing arrows across the whole country.

How does relief create heavy rainfall and a rain shadow?

What happens when moist air meets a mountain?

Orographic rainfall, also called relief rainfall, occurs when a mountain forces moist air upwards. Rising air expands and cools. Its moisture condenses, producing greater rainfall on the slope facing the arriving wind.

1. Moist winds approach a mountain barrier and meet its windward slope, the side directly exposed to those winds.
2. The barrier forces the air to rise. Expansion during ascent lowers its temperature.
3. Cooling allows water vapour to condense, producing cloud and rainfall on the windward side.
4. After crossing the crest, air descends on the leeward side and becomes warmer, reducing the likelihood of further rain.
5. The sheltered area consequently receives less rainfall and forms a rain-shadow region.

Case study: Why is the western coastal plain wetter than the plateau?

The Western Ghats obstruct the Arabian Sea branch. Their windward slopes and the western coastal plain receive very heavy rainfall, with a stated range of 250 to 400 centimetres. The abbreviation cm means centimetres, a unit used to express rainfall depth.

East of the Ghats, descending winds become warmer and less humid. Much less rain falls in this rain shadow. The contrast is caused by exposure to the same airflow on opposite sides of a barrier, rather than simply by different distances from the equator.

Case study: Why are the Khasi hills exceptionally wet?

A sub-branch of the Bay of Bengal monsoon strikes the Garo and Khasi hills in Meghalaya. The combination of moisture-bearing winds and relief produces exceptionally heavy rain. Mawsynram lies on the crest of the Khasi hills.

Cherrapunji and Mawsynram receive over 1,080 cm of rain in a year in the regional examples. This is a geographical illustration of very high rainfall, not a promise that each year has exactly the same total.

These two regional cases demonstrate the same broad control: the path of moist winds and their encounter with relief matter greatly. A mountain’s climatic effect depends on its position relative to the approaching airflow, not merely on its presence.

Why is monsoon rainfall uneven in amount and timing?

How does annual rainfall vary across India?

India’s average annual rainfall is about 125 cm, but the national average hides large differences. Windward mountain slopes and parts of the northeast are very wet, while western Rajasthan, Ladakh and some sheltered peninsular areas receive much less rain.

These are broad regional patterns. Do not assume that every location inside a named state receives exactly the same amount. Relief and the position of rainfall belts create differences within states as well as between them.

The legend distinguishes more than 200, 100 to 200, 50 to 100 and less than 50 centimetres. Dark shading marks the wet western coastal belt and northeast; dotted shading marks low-rainfall areas in the northwest and parts of the peninsula.

What is a break in the monsoon?

A break in the monsoon is a dry spell during the rainy season: rain may stop for one or more weeks after several rainy days. It differs from the burst, which is the sudden arrival of the rains.

In northern India, rain may fail when rain-bearing storms are not frequent along the monsoon trough. On the west coast, dry spells can occur when winds blow parallel to the coast. Causes therefore differ between regions.

The total amount of rain and its distribution through time are separate features. A seasonal total does not show whether rainfall was regular or interrupted by long dry periods. Such interruptions can create agricultural difficulties even within the rainy season.

What changes occur during the retreating monsoon?

Why does the southwest monsoon withdraw?

October and November are the main retreating monsoon months. As the Sun’s apparent position shifts southwards, the low-pressure trough over the Ganga plain moves south and the southwest monsoon weakens. Withdrawal proceeds across the country rather than occurring everywhere at once.

The season often brings clearer skies and a rise in temperature while the land remains moist. High temperature combined with high humidity produces oppressive conditions called October heat. It is the combination of warmth and moisture that makes the weather uncomfortable.

Temperatures begin to fall more rapidly in northern India during the second half of October. Much of the north becomes dry, while the eastern side of the southern peninsula receives important rainfall. A retreating monsoon therefore does not mean a rainless season throughout India.

Case study: Why does Tamil Nadu receive rain at this time?

The Tamil Nadu coast receives relatively little rain from the southwest monsoon because the Bay of Bengal branch runs approximately parallel to it and it lies in the rain shadow of the Arabian Sea branch.

During October and November, northeast winds cross the Bay of Bengal and collect moisture. They then bring rain to the Tamil Nadu coast. The ocean crossing is crucial: winds that began over land can become moisture-bearing before reaching another coast.

Cyclonic depressions associated with the Andaman Sea and Bay of Bengal also bring widespread rain to the eastern coast of the southern peninsula. Much of the Coromandel coast’s rainfall is associated with these depressions and cyclones.

The deltas of the Godavari, Krishna and Kaveri are vulnerable to destructive tropical cyclones. Rainfall in this season can therefore be both important for water supply and accompanied by damaging storms. Such cyclonic storms are less frequent in the Arabian Sea.

What are winter conditions and why does some winter rain occur?

How do winter temperature, pressure and winds differ?

The cold weather season usually begins by mid-November in northern India. December and January are the coldest months in the northern plains. Night temperatures can be very low and may fall below freezing in parts of Punjab and Rajasthan.

Distance from the sea contributes to strong winter cooling in the interior. Snowfall in the nearby Himalayan ranges can create cold-wave conditions. Southern coastal areas have a less clearly defined cold season because they are nearer the equator and moderated by the sea.

Winter brings relatively high pressure over northern India and lower pressure farther south. Winds move outwards from the northern high-pressure region. Relief modifies their direction: they are westerly or northwesterly along the Ganga valley and more clearly northeasterly over the Bay of Bengal.

Because much of this airflow begins over land, it carries little humidity. Most parts of India are consequently dry in winter. This generalisation must retain its exceptions, particularly winter disturbances in the northwest and moisture-bearing northeast winds near the southeastern coast.

What are western disturbances?

Western disturbances are eastward-moving weather disturbances associated with shallow cyclonic depressions originating over the eastern Mediterranean region. They travel across West Asia towards northwestern India, where they interrupt otherwise generally dry winter conditions.

They bring some rain to Punjab, Haryana, Delhi and western Uttar Pradesh, and snowfall to the Himalayas. Although the plains receive relatively small amounts, this rainfall is valuable for rabi crops, crops grown during the winter agricultural season.

Snow stored in the Himalayas also helps sustain river flow during summer. This links winter precipitation with water availability in a later season. Winter rain is therefore significant even though it supplies a smaller share than the main summer rains in much of India.

Note: Keep the two settings distinct: northwestern winter rain is associated with western disturbances, while the Tamil Nadu coast receives moisture from northeast winds crossing the Bay and from cyclonic systems.

How should temperature and rainfall data be interpreted?

Which measurements must be kept separate?

A climate table can describe monthly temperatures and rainfall. Read the place, period and units before calculating. The abbreviation mm means millimetres; 10 mm equals 1 cm. Rainfall amounts must use the same unit before they are added or compared.

Annual temperature range is the highest monthly mean temperature minus the lowest monthly mean temperature. It is different from a daily range and from the difference between absolute record temperatures. A large range suggests stronger seasonal contrast; location must still be considered.

Annual rainfall is obtained by adding the rainfall totals for all twelve months. The wettest month is the one with the largest monthly total. Missing entries must not automatically be counted as zero unless the table’s key explicitly says so.

Worked example: How are New Delhi’s mean temperatures calculated?

Worked example 1. New Delhi’s Safdarjung observatory data, based on observations from 1951 to 1980, give the following January and May values. The observatory is 216 metres above mean sea level. Here, m means metres.

Calculate the mean temperature for each month by averaging its mean daily maximum and minimum. Use January as the coldest month and May as the hottest month for the annual-range calculation in this example.

In these calculations, + means addition, ÷ means division, − means subtraction and = means equals.

Answer: January mean = (21.1 + 7.3) ÷ 2 = 14.2°C. May mean = (39.6 + 25.9) ÷ 2 = 32.75°C. Annual range = 32.75 − 14.2 = 18.55°C.

The record-temperature columns are not used to calculate these monthly means. Mixing a record maximum with a mean minimum would combine different measurements and produce a misleading result.

For rainfall interpretation, first identify when most rain occurs, then relate that pattern to wind direction, moisture supply and relief. A numerical result answers “how much”; a climatic explanation answers “why here” or “why in this season”.

How does the seasonal cycle affect life and agriculture?

How can the four seasons be compared?

The annual cycle links temperature, pressure, winds and precipitation. Each season changes the conditions inherited from the previous one: summer heating prepares low pressure, monsoon winds supply moisture, withdrawal alters circulation, and winter cooling strengthens continental high pressure.

Why does rainfall distribution matter to farming?

Agriculture depends strongly on timely and adequately distributed rainfall, especially where irrigation is limited. Regional differences in monsoon climate help support different crops. The seasonal arrival of rain therefore influences the agricultural cycle as well as day-to-day weather.

Rainfall variability can bring droughts or floods. A delayed arrival or prolonged break can reduce water availability, while a sudden heavy burst may encourage soil erosion. The effects depend on timing and intensity as well as the overall seasonal amount.

Winter rain from temperate disturbances benefits rabi crops in northern India. Summer thunderstorms also have local agricultural value, including rain for tea, jute and rice in Bengal and Assam and showers associated with coffee flowering in southern India.

Climatic differences are reflected in food, clothing and house types. India’s climate can therefore be understood as a connected seasonal system with strong regional variation. Explaining a place requires linking its season, location, winds, moisture sources and relief.

Glossary

• Weather — The momentary state of the atmosphere, including temperature, pressure, wind, humidity and precipitation.
• Climate — Average weather conditions and their characteristic patterns over a longer period of time.
• Monsoon — A seasonal reversal of wind direction associated with a characteristic annual climatic rhythm.
• Equable climate — A climate with relatively small temperature fluctuations, commonly associated with coastal moderation.
• Altitude — Height above mean sea level, an important control because temperature generally decreases with height.
• Pressure gradient — The change in atmospheric pressure across a distance, helping drive the movement of air.
• ITCZ — The Inter Tropical Convergence Zone, a low-pressure belt where trade winds meet and air rises.
• Coriolis force — The effect of Earth’s rotation that deflects moving air to the right in the Northern Hemisphere.
• Jet stream — A narrow band of fast-moving winds in the upper atmosphere that influences weather circulation.
• Orographic rainfall — Rain produced when moist air is forced to rise and cool over a mountain barrier.
• Rain shadow — A relatively dry area on a mountain’s leeward side, where descending air becomes warmer.
• Loo — Hot, dry, oppressive winds that blow across the northern plains during the hot weather season.
• October heat — Oppressive conditions caused by high temperature and humidity during the retreating monsoon season.
• Western disturbances — Eastward-moving weather disturbances from the Mediterranean region that bring winter precipitation to northwestern India.
• Annual temperature range — The difference between the highest and lowest monthly mean temperatures during a year.

Common errors and misconceptions

• Misconception: A monsoon means rainfall alone. Correct: Its defining feature is seasonal reversal of winds; moisture, wind route and relief influence the associated rainfall.
• Misconception: Every place in India has identical monsoon conditions. Correct: A common seasonal rhythm exists alongside major regional differences in temperature, rainfall amount and rainfall timing.
• Misconception: The monsoon burst and a monsoon break mean the same thing. Correct: The burst is the abrupt onset of rain; a break is a dry spell within the rainy season.
• Misconception: Northeast winds cannot bring rain because they originate over land. Correct: They can acquire moisture while crossing the Bay of Bengal and bring rain to the Tamil Nadu coast.
• Misconception: Winter is rainless throughout India. Correct: Western disturbances bring rain to the northwestern plains and snow to the Himalayas, despite generally dry winter conditions elsewhere.
• Misconception: The eastern side of the Western Ghats is equally wet. Correct: Descending air becomes warmer and produces less rain, creating a rain shadow on the leeward side.
• Misconception: Annual temperature range uses the highest and lowest recorded extremes. Correct: Use the highest and lowest monthly mean temperatures; record extremes describe a different measurement.
• Misconception: Normal onset dates specify what must happen every year. Correct: They describe a normal seasonal pattern; actual onset and rainfall behaviour vary between years.

Exam-style questions with model answers

Q1. Define monsoon and distinguish it from a monsoon break. [2 marks]

1. A monsoon involves a seasonal reversal in wind direction.
2. A monsoon break is a dry spell within the rainy season, when rainfall stops for one or more weeks after rainy days.

Q2. Explain how latitude, altitude and distance from the sea influence India’s temperature patterns. [3 marks]

1. Latitude affects heating: southern tropical India generally has smaller temperature ranges than northern areas farther from the equator.
2. Temperature generally decreases with altitude, so mountain locations are cooler than plains at similar latitudes.
3. The sea heats and cools slowly, moderating coastal temperatures. Inland places lack this strong influence and experience greater seasonal contrasts between summer and winter.

Q3. Explain the sequence by which summer heating produces moisture-bearing southwest monsoon winds over India. [5 marks]

1. Land heats more rapidly than the ocean in summer. Strong heating intensifies low pressure over northwestern India, while the ocean to the south has relatively higher pressure.
2. The Inter Tropical Convergence Zone shifts northwards and helps establish the monsoon trough over northern India, organising the summer circulation.
3. Southeast trade winds from the Southern Hemisphere cross the equator towards this low-pressure region and collect moisture over the ocean.
4. Earth’s rotation deflects the moving air to its right in the Northern Hemisphere. It therefore approaches India as southwest monsoon flow.
5. The winds enter through Arabian Sea and Bay of Bengal branches. Relief and regional pressure conditions modify their routes and distribute the resulting rain.

Q4. Explain why the western slopes of the Western Ghats receive heavy rain while the region immediately to their east receives less. [3 marks]

1. The western slopes face moisture-bearing Arabian Sea monsoon winds. The mountain barrier forces these winds to rise.
2. Rising air expands and cools, allowing moisture to condense and produce heavy rainfall on the windward slopes and adjoining coastal plain.
3. After crossing the crest, air descends and becomes warmer. Rainfall decreases, leaving the eastern, leeward region in a rain shadow.

Q5. Explain Tamil Nadu’s relatively dry southwest monsoon conditions and its important October-November rainfall. [4 marks]

1. The Bay of Bengal branch of the southwest monsoon flows approximately parallel to the Tamil Nadu coast, limiting rainfall there.
2. The coast also lies in the rain shadow of the Arabian Sea branch after that airflow crosses the Western Ghats.
3. In October and November, northeast winds cross the Bay of Bengal, acquire moisture and bring rain to the coast.
4. Cyclonic depressions and tropical cyclones also contribute significantly to rainfall along the Coromandel coast during this season.

Q6. Name the origin region of western disturbances and explain two effects of their winter precipitation in India. [3 marks]

1. Western disturbances are associated with depressions originating over the eastern Mediterranean region and travelling eastwards towards northwestern India.
2. Their rain over the northwestern plains benefits rabi crops. Even relatively small winter totals can be agriculturally valuable during the otherwise generally dry season.
3. They also produce Himalayan snowfall. The stored snow helps sustain river flow during the later summer months.

Q7. For New Delhi, January’s mean daily maximum and minimum are 21.1°C and 7.3°C; May’s are 39.6°C and 25.9°C. Calculate each monthly mean by averaging the maximum and minimum. Taking January as the coldest month and May as the hottest, calculate the annual temperature range. [3 marks]

1. January mean = (21.1 + 7.3) ÷ 2 = 14.2°C. This averages the two January mean daily values supplied.
2. May mean = (39.6 + 25.9) ÷ 2 = 32.75°C, using the same calculation for May.
3. Annual temperature range = hottest monthly mean minus coldest monthly mean = 32.75 − 14.2 = 18.55°C. The calculation uses monthly means, not absolute record temperatures.

Q8. The January temperature examples for Agra and Darjiling are 16°C and 4°C respectively. They lie at approximately the same latitude, and Darjiling is at a higher altitude. Calculate their temperature difference and explain why latitude alone cannot account for it. [2 marks]

1. The difference is 16 − 4 = 12°C.
2. Their similar latitude does not explain the contrast. Darjiling’s higher altitude helps explain its lower temperature, because temperature generally decreases with height.

Key takeaways

• India’s climate has a common monsoonal rhythm, but temperatures, rainfall totals and rainy-season timing vary greatly between regions.
• Latitude, altitude, distance from the sea, relief and the Himalayas interact to shape regional climatic conditions.
• Summer heating and the northward movement of the convergence zone help draw moisture-bearing, cross-equatorial winds towards India.
• The Arabian Sea and Bay of Bengal branches follow different routes, modified by relief and regional pressure conditions.
• Windward slopes receive heavier orographic rain, while descending air creates relatively dry conditions on leeward slopes.
• Tamil Nadu’s rainfall pattern differs from much of India because northeast winds and cyclonic systems bring important autumn rain.
• Western disturbances provide valuable winter rain for northern rabi crops and snowfall that helps sustain Himalayan river flow.
• Interpret climate data using the stated units and period; distinguish monthly means, record temperatures, daily range and annual range.

Test yourself

Why does a coastal place usually have smaller seasonal temperature contrasts than an inland place?

The sea heats and cools more slowly than land, moderating nearby temperatures and reducing seasonal extremes.

What does ITCZ stand for, and why does its summer movement matter?

Inter Tropical Convergence Zone. Its northward shift helps establish the monsoon trough and organise summer winds over India.

How does a monsoon burst differ from a break?

A burst is the abrupt arrival of monsoon rain; a break is a dry spell during the rainy season.

Which hot-season wind is dry, and which local showers help mangoes ripen?

The loo is hot and dry. Mango showers in Kerala and coastal Karnataka help mangoes ripen early.

Why does air descending east of the Western Ghats produce less rain?

Descending air becomes warmer, reducing its relative humidity and leaving a comparatively dry rain-shadow region.

What produces October heat?

High temperatures combine with high humidity over still-moist land during the retreating monsoon, producing oppressive weather.

What is the source of northwestern India’s winter rainfall?

Western disturbances associated with eastward-moving depressions from the Mediterranean region bring rain to the northwestern plains.

Which temperatures are used to calculate annual temperature range?

Subtract the lowest monthly mean temperature from the highest monthly mean temperature, using consistent units.