Climate of India

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Climate

Climate refers to the average weather conditions of a particular place observed over a long period of time, typically 35 years or more. It includes patterns of temperature, rainfall, humidity, wind, and atmospheric pressure recorded over the years.

 

Difference Between Weather and Climate:

 

• Weather: Weather is short-term (minutes to month) change in the atmosphere. It includes sunshine, rain, cloud cover, winds, hail, show, sleet etc.

 

• Climate: Climate is a long-term pattern of weather in a particular area or it is also defined as the average atmospheric conditions of a particular region over a considerable period, usually taken over 35 years. India is considered as a country with Tropical monsoon climate.

 

In simple words, climate is the long-term ‘mood’ of the atmosphere, while weather is the short-term ‘behavior.’

 

Key Terms Related to Climate

 

• Monsoon: A seasonal wind system, characterized by reversal of wind direction, leading to distinct wet and dry seasons. The word Monsoon originates from the Arabic word ‘mausim’ which means seasonal reversal in the direction of winds. The Arabian geographer Al Masoodi was the first to study monsoon. Example- India’s Southwest Monsoon brings 75%–90% of the annual rainfall.

 

• Rainfall: Amount of precipitation received in a region, either in mm or cm, usually measured annually or seasonally. Example- In India, average annual rainfall is about 120 cm.

 

• Precipitation: Any form of water (liquid or solid) falling from the atmosphere like rain, snow, hail, sleet, drizzle, etc. is called Precipitation.

 

• Humidity: The amount of moisture (water vapor) present in the air. High humidity = More sticky, moist air and it is measured by hygrometer.

 

• Temperature: The degree of heat present in the atmosphere. It influences evaporation, air pressure, wind patterns, and crop types.

 

• Diurnal Range of Temperature: The difference between the highest (day) and lowest (night) temperature in 24 hours.

 

• Annual Range of Temperature: The difference between the hottest and coldest month’s temperature in a year.

 

• Cyclone: A large-scale air mass with a low-pressure center, rotating inward.

 

• Jet Streams: High-altitude, fast-moving air currents that influence the onset and withdrawal of monsoon in India.

 

• Western Disturbances: A type of mid-latitude cyclone originating in the Mediterranean region, bringing winter rain to North-West India, especially Punjab, Haryana, and western Uttar Pradesh.

 

• ITCZ (Inter-Tropical Convergence Zone): A low-pressure zone near the equator where trade winds converge, influencing monsoon formation and movement in India.

 

• El-Nino & La-Nina: Global ocean-atmosphere phenomena in the Pacific Ocean affecting Indian monsoon. El-Nino- weaker monsoon, drought-like conditions, and La-Nina- stronger monsoon, more rainfall.

 

• Isotherm: A line joining places having equal temperature at a given time or over a given period.

 

• Isobar: A line joining places with equal atmospheric pressure.

 

• Isohyet: A line connecting areas that receive equal rainfall.

 

• Isobath: A line joining points in water bodies having equal depth below sea level.

 

• Isotach: A line connecting locations with equal wind speed.

 

• Isohel: A line connecting areas that receive equal duration of sunshine. Isohels are the Isopleths of sunshine.

 

Factors Affecting the Climate of India

India has a diverse climate, from snow in the Himalayas to tropical heat in Kerala, from deserts in Rajasthan to heavy rains in Meghalaya. This diversity is due to the combined effect of several climatic controls. The main factors that influence the climate of India:

 

Latitude

• India is located between 8°4′N and 37°6′N.
• The Tropic of Cancer (23½°N) passes almost through the middle of Indian dividing the country into: Tropical zone (south of Tropic) and Sub-tropical zone (north of the Tropic).
• Therefore, southern India has a tropical climate, while northern India has a more extreme (continental) climate.

 

Altitude

• India has a vast altitudinal range, from sea level to the mighty Himalayas (8,000+ m).
• Hill stations like Shimla, Darjeeling, and Ooty remain cool due to altitude despite being in tropical regions.

 

Physiography

• Physiography of India also affects the climate of India. The western part of the Aravalli Mountains and the eastern part of the Western Ghats are areas which receive lesser rainfall, high altitude region also receive low rainfall.

 

Distance from the Sea

• Coastal areas of Mumbai, Chennai etc. have a moderate climate due to sea’s influence.
• Interior parts of India like Delhi, Nagpur, etc. experience extreme temperatures; hot summers and cold winters due to continental climatic influence.

 

Presence of the Himalayas

• The Himalayas protect India from cold Central Asian winds, allowing for a warmer winter compared to same latitudes elsewhere.
• They help trap monsoon winds, resulting in heavy rainfall in the Indo-Gangetic plains.
• Their height and orientation shape wind patterns and rainfall distribution.

 

Pressure and Wind Systems

• The differential heating of land and sea causes changes in pressure systems, which directly affect wind patterns in India.
• Major wind system that influencing Indian climate are Regular wind, Irregular wind, Local wind, and Periodic wind.

 

Jet Streams

• Subtropical Westerly Jet Stream: Present over the Himalayas during winter. It is responsible for Western Disturbances in north India.
• Tropical Easterly Jet Stream: Develops during the Southwest Monsoon. It is guiding monsoon winds across the country.

 

Ocean Currents

• Warm and cold currents influence temperature and rainfall of coastal areas.

 

El-Nino and La-Nina

• Global ocean-atmosphere phenomena in the Pacific Ocean affecting Indian monsoon by warming and cooling.
• El-Nina weak monsoon and influence drought in India and La-Nina make the monsoon strong and influence more rainfall than normal rainfall in India.

 

Southern Oscillation

• It has been observed that changes in the pressure conditions over the Southern Ocean also affects the monsoon.
• Generally, when the tropical south Pacific Ocean experiences high pressure, the tropical south eastern Indian ocean experiences low pressure.

 

Western Disturbances

• Originating in Mediterranean Sea, these are extra-tropical cyclones. Enter India via Pakistan during winter.
• Bring rainfall to north-western India.

 

Classification of Indian Climate

India has a diverse climate, ranging from tropical in the south to temperate and alpine in the north. Dr. W. Koppen classified the Indian Climate into 9 types based on:

1. Annual and monthly average temperature.
2. Annual and monthly average rainfall.
3. Native vegetation.

 

Classification of Indian Climate According to Koppen

Koppen has divided Indian Climate into Five main climatic groups and denoted it with capital alphabets:

 

A- Tropical
B- Dry
C- Temperate with mild winters
D- Continental with severe winters
E- Polar

 

All these main groups are further sub-categorized based on seasonal rainfall and small alphabet is assigned along with main group. For example: a (hot summer), c (cool summer), f (no dry season), w (winter dry), s (summer dry), g (Ganges type with hottest month before summer rainy season), h (average temperature never exceed 18-degree c) and m (monsoon with short dry season).

 

Amw - Tropical Monsoon Climate with Dry Winter

• A = Tropical, m = Monsoon, w = dry winter.
• Found in: Western Ghats (Kerala, Karnataka), North-Eastern states, northern parts of West Bengal, and Andaman and Nicobar Islands.
• In these areas, there are very high rainfall during monsoon about 300 cm rainfall in summers while the winter remains dry.

 

Aw - Tropical Savanna Climate

• A = Tropical, w = dry winter.
• Found in: Central and Southern Peninsular India, including Maharashtra, MP, Telangana, Chhattisgarh, Odisha.
• Moderate rainfall, mostly in monsoon season about 75 cm.
• Distinct wet (summer) and dry (winter) seasons.

 

As - Tropical Savanna Climate with Dry Summer

• A = Tropical, s = dry summer.
• Found along: Eastern Coastal areas – Tamil Nadu, South-East Andhra Pradesh (mainly Coromandel Coast).
• Dry summer, rainfall from retreating monsoon and cyclones (from Oct–Dec) about 75-100 cm in winter.
• Reverse pattern compared to Aw.

 

BShw - Semi-Arid (Steppe) Climate

• B = Dry, S = Semi-arid (Steppe), h = hot, w = dry winter.
• Found in: Leeward side of Western Ghats, Telangana, Rain-shadow areas of Karnataka, Maharashtra.
• Less than 75 cm rainfall.
• Short wet season, long dry season.

 

BWhw - Arid (Desert) Climate

• B = Dry, W = Desert, h = hot, w = dry winter.
• Found in: Thar Desert (Western Rajasthan), some parts of Gujarat.
• Rainfall: <25 cm annually.
• High diurnal range, extreme aridity.

 

Cwg - Humid Subtropical Climate with Dry Winter

• C = Warm Temperate, w = dry winter, g = hot summer.
• Found in: Northern Plains; Delhi, Uttar Pradesh, Bihar, parts of Assam, North Bengal.
• Hot summer, cool winter, rainfall mostly in monsoon.
• Western Disturbances bring rain in winter.

 

Dfc / Dfd - Humid Snowy Forest Climate

• D = Snow (cold), f = sufficient rainfall, c/d = severe winters.
• Found in: Kashmir Valley, Himachal Pradesh, Uttarakhand (higher altitudes).
• Cold and long winters, moderate and short summer.
• Snowfall in winter.

 

ET - Tundra Climate

• E = Polar, T = Tundra (very cold).
• Found in: Mountainous areas of Uttarakhand at an altitude from 3000 m to 5000 m.
• Temperature stays below 10°C even in summer and the precipitation is in the form of snow in winters.

 

E - Polar Type

• E = Polar type.
• Found in: Ladakh, Higher Himalayas (above snowline).
• No tree growth, very little precipitation.
• The temperature is less than 0°C throughout the year.

 

Indian Meteorological Department (IMD)’s Classification

The IMD classifies the climate of India into four broad types, based on seasonal patterns:

 

Table 1: IMD's Climate classification based on seasonal patterns.

 

 

Thornthwaite’s Classification

• Based on precipitation effectiveness and temperature efficiency.
• Divides India into: Arid, Semi-Arid, Sub-Humid, Humid zones.
  • Arid zones – Western Rajasthan.
  • Semi-arid – Deccan Plateau.
  • Humid subtropical – Ganga plains.
  • Tropical monsoon – Coastal and Northeast India.
  • Alpine/Tundra – Himalayas and Ladakh region.

 

Wind System of the Earth (Based on Indian Climate)

Winds are horizontal movements of air from high pressure to low pressure areas. They are classified into:

• Regular (or Permanent) Winds
• Irregular (Temporary) Winds
• Periodic Winds
• Local Winds

 

Regular or Permanent Winds

These winds blow consistently throughout the year in a particular direction and are caused by the Earth's rotation and solar heating.

 

Trade Winds (Tropical Easterlies)

• Blow from Subtropical High (30° N/S) to Equatorial Low (0°).
• Direction: NE in Northern Hemisphere, SE in Southern Hemisphere.
• Very steady and strong, used by traders in the past.
• Important for Indian monsoon system. South-West Monsoon of India is the part of South-East Trade wind.

 

Westerlies

• Blow from Subtropical High (30°) to Subpolar Low (60°).
• Direction: SW in Northern Hemisphere, NW in Southern Hemisphere.
• Stronger in Southern Hemisphere due to fewer land masses.
• Drive cyclonic systems in mid-latitudes.

 

Polar Easterlies

• Originate from Polar High (90°) to Subpolar Low (60°).
• Very cold and dry winds.
• Direction: North-East in Northern Hemisphere, and South-East in Southern Hemisphere.

 

Irregular or Temporary Winds

These winds occur suddenly due to atmospheric disturbances like pressure differences or storms.

 

Cyclone

• Formed in a low-pressure zone.
• Mainly shown in summer seasons.
• Winds move inward and anticlockwise in Northern Hemisphere (clockwise in Southern Hemisphere).
• Brings cloudy skies, rain, storm, and another climatic phenomenon.
• Examples: Tropical cyclones, and Temperate cyclones.

 

Table 2: Tropical Cyclone name and their locations.

 

 

Anticyclone

• Formed in a high-pressure zone.
• Mainly shown in winter seasons.
• Winds move outward and clockwise in Northern Hemisphere (anticlockwise in Southern Hemisphere).
• Brings clear, dry weather.

 

Local Winds

These are short-distance winds, caused by local differences in temperature and pressure. They may be hot or cold.

 

Table 3: Hot and Cold local wind’s Name and Location

 

Periodic Winds

These winds change direction periodically, usually with seasons or day/night. Periodic winds are three types:

 

Sea Breeze

• A sea breeze is a cool, moist wind that blows from the sea (ocean or large water body) towards the land during the daytime.
• It is a type of periodic wind, caused by differential heating of land and water. During the day, land heats up faster than water. The air above the land becomes hot, lighter, and rises, creating a low-pressure area. The sea remains cooler, and the air above it stays cooler and denser, forming a high-pressure zone. Cool air from the high-pressure sea region moves towards the low-pressure land region, this movement is called a Sea Breeze.
• Sea breeze common in coastal regions such as Eastern and Western Coastal region in India.

 

Land Breeze

• A land breeze is a hot wind that blows from land towards the sea during the night, caused by the differential cooling of land and sea.
• At night, land loses heat faster than water due to its lower specific heat capacity. The air above land cools down quickly, becomes denser, and creates a high-pressure zone. The sea retains heat longer, and the air above it remains warmer, rising and forming a low-pressure zone. As a result, cooler air from the land flows towards the sea, this airflow is called a Land Breeze.

 

Monsoon

• Indian Monsoon is marked by seasonal shift caused by different heating of land and water body (sea).
• Summer Monsoon: South-West direction (brings rainfall to all over India).
• Winter Monsoon: NE direction (generally dry except Tamil Nadu coast).

 

Key Facts:

• ITCZ: The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt located near the Equator (00 – 100 N/S), where the northeast trade winds of the Northern Hemisphere and the southeast trade winds of the Southern Hemisphere converge.

 

• Horse Latitudes: Horse Latitudes refer to subtropical high-pressure belts located between 25° and 35° latitudes in both the Northern and Southern Hemispheres.

 

• Coriolis Force: The Coriolis Force is an apparent force caused by the rotation of the Earth, which deflects the path of moving objects, such as winds and ocean currents.

 

• Ferrel’s Law: Any object or fluid moving freely above the Earth’s surface is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Earth’s rotation.

 

Indian Monsoon

The term "Monsoon" comes from the Arabic word ‘Mausim’, meaning season. In the Indian context, monsoon refers to the seasonal reversal of winds, particularly over the Indian subcontinent, which brings heavy rainfall during summer and dry conditions in winter in the month of June and July.

 

Indian Monsoon is the most prominent example of the world’s monsoon system, which primarily affects season, vegetation, and lifestyle of the economy. That is why Monsoon is the lifeline of Indian agriculture, economy, and ecology.

 

Origin and Mechanism of Indian Monsoon

The mechanism of Indian monsoon is influenced by a complex set of factors:

 

Differential Heating of Land and Sea

• In summer, the Indian landmass heats up faster than the surrounding seas.
• This creates a low-pressure zone over northern India and a high-pressure zone over the Indian Ocean.
• The pressure difference pulls moist air from the ocean towards the land — forming South-West Monsoon winds.

 

Shift of Inter-Tropical Convergence Zone (ITCZ)

• ITCZ shifts northward during summer, bringing a zone of convergence and rising air near the Himalayas, causing rainfall.

 

Presence of High Pressure over the Southern Indian Ocean

• A high-pressure zone over Mascarene High (near Madagascar) helps in pushing the moist winds towards India.

 

Jet Streams

• Subtropical Westerly Jet Stream (STWJ): Influences the withdrawal of monsoon.
• Tropical Easterly Jet Stream (TEJ): Plays a role in onset of monsoon.

 

El Nino–Southern Oscillation (ENSO)

• Warming or cooling of Pacific Ocean affects Indian Monsoon.
• El Nino leads to weak monsoon, while La Nina may cause heavy rainfall.

 

Branches of South-West Monsoon

Once it reaches India, the South-West Monsoon splits into two branches:

 

Arabian Sea Branch

• Hits the Western Ghats (Kerala, Karnataka, Goa, Maharashtra) and causes orographic rainfall.
• Moves toward Gujarat, Madhya Pradesh, and finally meets the Bay of Bengal branch at the Northern plains.

 

Bay of Bengal Branch

• Moves north-eastwards, hits Assam and Meghalaya, then deflects westward due to the Himalayas.
• Causes rainfall in northern plains (Bihar, Uttar Pradesh, Delhi, Punjab).

 

Retreating or North-East Monsoon

• Occurs after September, when land begins to cool.
• Winds blow from land to sea (NE direction).
• Causes rainfall over Tamil Nadu, Andhra Pradesh, due to moisture from Bay of Bengal.
• Associated with cyclonic activities in the Bay of Bengal.

 

Factors Affecting Indian Monsoon

• Latitude (Tropic of Cancer cuts across India).
• Altitude (Western Ghats, Himalayas impact rainfall)
• Distance from the sea (Coastal vs interior)
• Jet Streams and ENSO
• Snow cover on Himalayas

 

Characteristics of Indian Monsoon

• Seasonal Reversal: Winds reverse direction between summer and winter.
• Uneven Distribution: Some areas like Cherrapunji receive >1000 cm; others like Rajasthan <20 cm.
• Orographic Rainfall: Caused by barriers like the Western Ghats and Himalayas.
• During monsoon season, rainfall decreases from the Ganga delta to Punjab plains, because monsoon current moves westward along the Ganga plains and become drier.

 

Importance of Monsoon in India

• Agriculture: 60% of Indian agriculture is rain-fed.
• Water Resources: Fills rivers, reservoirs, groundwater.
• Power Generation: Hydropower depends on monsoon-fed rivers.
• Rural Economy: Monsoon drives rural demand and employment.

 

Key Facts:

• First monsoon arrival in India occurs over the Andaman & Nicobar Islands around 20th–21st May.
• The first Indian state to receive monsoon rains is Kerala, typically around 1st June.
• The mainland onset of the Southwest Monsoon is officially marked at Kerala on 1st June.
• West Bengal generally receives monsoon rainfall by around 8th June.
• The amount and intensity of Monsoon in India are affected by tropical depressions.
• The highest temperature is found in the earth at 2 p.m.
• Opposite climate of Monsoon climate is Medeterian Climate.
• Duration of South-West Monsoon is 100-120 days.
• Mango Shower: Pre-monsoonal showers at the end of summer, helps in the early ripening mangos in Kerala and Coastal Karnataka.
• Blossom Shower: Result in the blossoming of coffee flowers in Kerala.
• Nor-Westerlies:  Nor-Westerlies, locally known as ‘Kalbaisakhi’ in West Bengal and ‘Bardoli Chheerha’ in Assam, are violent local thunderstorms that occur during the pre-monsoon summer season in parts of eastern and north-eastern India. Beneficial for Tea, Jute and Rice cultivation.
• Andaman and Nicobar receives rainfall from both South-West and North-West Monsoon.

 

Precipitation

Precipitation is the process by which condensed water vapour in the atmosphere falls to the Earth in various forms like rain, snow, sleet, hail, dew, and frost. In India, rainfall is the most common form of precipitation. India experiences three main types of rainfall, based on the mechanism of formation:

 

1. Convectional Rainfall.
2. Orographic Rainfall.
3. Cyclonic Rainfall.

 

Convectional Rainfall

• Occurs when the land surface heats up intensely, causing the air above to rise, cool, and condense into cumulonimbus clouds, leading to sudden, heavy showers.
• Localized and short duration rain, often with thunder and lightning.
• It shows in the Congo basin, the Amazon basin and the Island of South-East Asia.
• It rains in equatorial region at 4’O clock in evening daily, so it is called as the 4’O clock rainfall or Equatorial rainfall (00 - 100).
• Occurs in pre-monsoon summer months.
• Common in peninsular India (in Tamil Nadu, Karnataka, and Kerala). Andaman and Nicobar also receive Convectional Rainfall, because of its latitudinal extension.
• Examples: Kalbaisakhi (Nor ’westers) in West Bengal & Assam, Blossom Showers in Western Ghats etc.

 

Orographic Rainfall (Relief Rainfall)

• Occurs when moist air masses from sea are forced to rise over mountain barriers (e.g., Western Ghats or Himalayas). As the air rises, it cools, condenses, and causes heavy rainfall on the windward side of mountains.
• Most common type during the southwest monsoon. Windward side gets heavy rainfall and Leeward side gets little rainfall.
• Mawsynram in Meghalaya's Khasi Hills receives the highest average rainfall in the world (around 1187 cm/year). It receives rainfall mainly from the Bay of Bengal branch of the Southwest Monsoon.
• Cherrapunji, located nearby, is the second wettest place in the world. It was once the wettest before Mawsynram surpassed it.
• Orographic rainfall is the most dominant type of rainfall in India, especially during the Southwest Monsoon.
• Windward sides: Mahabaleshwar, Mawsynram, Cherrapunji, Darjeeling, Arunachal Pradesh etc.
• Leeward side: Pune, Solapur, Rayalaseema, Ladakh, Lahaul-Spiti etc.

 

Cyclonic Rainfall (Frontal Rainfall)

• Caused due to the interaction of warm and cold air masses. The warm moist air is lifted, cools, and condenses to cause rainfall. In India, it is mostly associated with tropical and temperate cyclones.

 

• Tropical Cyclones:

  • Originate in Bay of Bengal and Arabian Sea.
  • Mainly affect eastern coastal states (Andhra Pradesh, Odisha, Tamil Nadu, West Bengal).
  • Occur during post-monsoon (Oct–Dec) and pre-monsoon (April–May). Cyclone of the Bay of Bengal are common during the Early monsoon.
  • Bring intense rainfall, strong winds, and sometimes floods.

• Temperate Cyclones (Western Disturbances):

  • Originate over the Mediterranean Sea.
  • Travel eastwards and enter North India via **Afghanistan and Pakistan.
  • Affect Punjab, Haryana, Delhi, Rajasthan, Uttarakhand, Himachal Pradesh, and western UP.
  • Occur during winter months (Dec–Feb).
  • Cause light to moderate winter rainfall, beneficial for rabi crops (especially wheat).
  • Winter Rainfall in Punjab: Panjab gets rainfall in Winter months due to the Winter Monsson. The source of winter rainfall for Panjab is also the cyclonic rain received from Western Disturbances entering the Indian sub-continent from Pakistan sides from North-West Monsoon.

 

Key Facts:

• A ‘Rainy Day’ is defined by the Indian Metrological Department (IMD) as a day when the total rainfall received is more than 2.5 mm in a 24-hour period at a given location.
• Indian Metrological Department (IMD) is located in New Delhi.
• Odisha faced/faces maximum disaster.
• Andhra coast faced the maximum number of cyclones.
• Tsunami warning centre in India is located in Hyderabad.
• The most flood prone state of India is Bihar by Kosi River.
• The first Disaster Management Training Institution of the country is being established at Latur, Maharashtra.
• The Daily weather map of India is prepared and printed at Pune.