Menu Top


World Climate And Climate Change (India Focus)

Koeppen’s Scheme Of Classification Of Climate

The Köppen climate classification is one of the most widely used systems for classifying the Earth's climates. Developed by Wladimir Köppen, it uses letters to denote different climate types based on temperature, precipitation, and seasonality. The system has been refined over time, but the original structure remains influential.

The classification is divided into five main groups, denoted by capital letters:

Each main group is further subdivided using a second letter (typically lowercase) to denote precipitation patterns, and sometimes a third letter for temperature characteristics.

Tropical Wet Climate (Af)

Characteristics: Hot and humid throughout the year, with high rainfall that is evenly distributed. No distinct dry season.

Indian Context: Found in regions of very high rainfall, such as the Western Ghats and the northeastern parts of India (Assam, Meghalaya). These areas experience lush, dense evergreen forests.

Tropical Monsoon Climate (Am)

Characteristics: Hot and humid for most of the year, with a distinct short dry season. High annual rainfall, often concentrated in the monsoon months.

Indian Context: Prevalent in much of India, especially the west coast and the eastern coast, which receive heavy monsoon rainfall.

Tropical Wet and Dry Climate (Aw)

Characteristics: Hot throughout the year, with distinct wet and dry seasons. The dry season is more pronounced than in Am climates.

Indian Context: Found in the interior of India, such as parts of the peninsula, Rajasthan, and the northern plains, where rainfall is moderate and seasonal.

Dry Climates : B

Characteristics: Evaporation exceeds precipitation. These climates are defined by aridity.

Subtropical Steppe (BSh) And Subtropical Desert (BWh) Climates

Characteristics:

Indian Context: Primarily found in the Thar Desert of Rajasthan and parts of Gujarat.

Warm Temperate (Mid-Latitude) Climates-C

These climates are found in the mid-latitudes and have moderate temperatures.

Humid Subtropical Climate (Cwa)

Characteristics: Hot, humid summers with abundant rainfall, and mild or cool winters with less rainfall.

Indian Context: Found in the northern plains and parts of the peninsula that experience monsoon influence but also have milder winters.

Mediterranean Climate (Cs)

Characteristics: Hot, dry summers and mild, wet winters.

Indian Context: Not significantly present in India, as India's climate is dominated by monsoonal influences. Some very localized effects might be seen in the far northwest.

Humid Subtropical (Cfa) Climate

Characteristics: Hot, humid summers and mild winters with rainfall in all seasons.

Indian Context: Found in the northeastern parts of India, which receive rainfall throughout the year, although with monsoon peaks.

Marine West Coast Climate (Cfb)

Characteristics: Mild summers and mild, wet winters. Consistent rainfall throughout the year.

Indian Context: Not present in India. This climate is typically found on the western coasts of continents in the mid-latitudes.

Cold Snow Forest Climates (D)

These climates are found in the mid-latitudes and higher latitudes, characterized by cold winters with snow and warm summers.

Cold Climate With Humid Winters (Df)

Characteristics: Cold winters with snow, and mild to warm summers with rainfall throughout the year.

Indian Context: Parts of the Himalayan region, especially at higher altitudes where temperature is low and precipitation (snow) occurs in winter.

Cold Climate With Dry Winters (Dw)

Characteristics: Cold winters with dry conditions and snow, and warm summers.

Indian Context: Found in the interior higher reaches of the Himalayas, such as Ladakh and Himachal Pradesh, where winters are severe and dry.

Polar Climates (E)

These climates are found at high latitudes (polar regions) or at very high altitudes.

Tundra Climate (ET)

Characteristics: Extremely cold winters and short, cool summers. Only low-lying vegetation like mosses and lichens can grow.

Indian Context: Found at the highest altitudes in the Himalayas, above the timberline, often referred to as alpine meadows.

Ice Cap Climate (EF)

Characteristics: Extremely cold with permanent ice and snow. Average temperature of all months is below 0°C.

Indian Context: The permanent snow-covered areas of the Himalayas, above 6,000 meters.

Highland Climates (H)

Characteristics: Climates that vary significantly with altitude. Temperature decreases and precipitation generally increases with altitude, but these patterns can be complex due to windward/leeward effects and exposure.

Indian Context: The entire Himalayan region exhibits Highland climates, with rapid changes in temperature, precipitation, and vegetation based on elevation and exposure.


Factors Determining The Climate Of India

India's climate is a result of a complex interplay of several geographical and atmospheric factors:

Factors Related To Location And Relief

1. Latitude: India lies in the tropics, with the Tropic of Cancer passing through its center. This ensures high temperatures throughout the year in the southern parts. The northern parts fall in the subtropical region, experiencing more distinct seasonal temperature variations.

2. Altitude: The Himalayas in the north play a crucial role. Their immense height causes temperatures to decrease significantly with increasing elevation, creating distinct altitudinal climatic zones. They also act as a barrier against cold continental winds from Central Asia.

3. Relief Features: The diverse topography – mountains, plains, plateaus, deserts, and coastal areas – influences temperature, rainfall patterns (e.g., orographic rainfall on windward slopes of the Western Ghats), and wind distribution.

4. Distance from the Sea: Coastal areas experience a maritime or equable climate (moderate temperatures), while inland areas have a continental climate (greater temperature variations). India's extensive coastline moderates the climate of the peninsular region.

5. Upper Air Circulation: The development of the westerly jet stream during winter and the easterly jet stream associated with the Indian monsoon significantly influence weather patterns.

Factors Related To Air Pressure And Wind

This category is crucial for understanding the Indian monsoon, which is the dominant feature of India's climate.

1. Differential Heating of Land and Sea: Land heats up and cools down faster than water. This creates seasonal pressure differences between the Asian landmass and the Indian Ocean.

2. Pressure and Winds:

3. Jet Streams:

4. Tropical Cyclones: These are low-pressure systems that form over the Bay of Bengal and the Arabian Sea, bringing heavy rainfall and strong winds to the coastal areas, particularly during the monsoon season and its transition periods.

5. Western Disturbances: Cyclonic disturbances originating from the Mediterranean region move eastward across Iran, Afghanistan, and Pakistan. They are drawn towards India by the westerly jet stream during winter and bring light rainfall and snowfall to the northern and northwestern parts of India.

Mechanism Of Weather In The Winter Season

1. High Pressure over Northwest India: A high-pressure region develops over northwestern India due to the dominance of continental polar air masses. This causes the dry, cold winds to blow from land towards the seas.

2. Westerly Winds: The surface winds blowing from land are dry and cold. However, the western jet stream influences the upper atmosphere.

3. Western Disturbances: These are the primary cause of winter precipitation in northern and northwestern India. They move towards India from the west, bringing:

4. Northeast Monsoon: While winds generally blow from land to sea, some moisture is picked up from the Bay of Bengal, causing a limited amount of rainfall in Tamil Nadu and adjoining areas of Andhra Pradesh, Karnataka, and Kerala during the winter season (October to December).

5. Temperature: Clear skies and dry weather prevail, leading to pleasant days and cold nights. Frost is common in the northern plains.

Mechanism Of Weather In The Summer Season

1. Low Pressure over North India: Intense solar heating during March to May causes the formation of a deep low-pressure area over northwestern India and Pakistan.

2. Differential Heating: The Indian subcontinent heats up much more intensely than the surrounding oceans.

3. Shift of Westerly Jet Stream: By April-May, the westerly jet stream shifts northwards to the Tibetan plateau.

4. Easterly Jet Stream: A strong easterly jet stream develops over the Peninsula. This easterly jet is crucial for the monsoon mechanism.

5. Pre-monsoon Conditions: In the hot weather season, hot dry winds called 'Loo' blow across the northern plains. Localized thunderstorms, often accompanied by strong winds and hail, are common in parts of India (e.g., 'Kalbaisakhi' in Bengal, 'Norwesters' in Assam, 'mango showers' in Kerala and Karnataka).

6. Formation of Monsoon Trough: The low-pressure area over northwestern India intensifies, forming a monsoon trough.

7. Incoming Monsoonal Winds: The pressure difference between the high-pressure area over the southern Indian Ocean and the low-pressure area over northwestern India causes the southwest monsoon winds to blow from the ocean towards the land.

Inter Tropical Convergence Zone (ITCZ)

Definition: The Inter Tropical Convergence Zone (ITCZ) is a broad, trough of low atmospheric pressure that is located near the equator. It is formed by the convergence of the northeast trade winds of the Northern Hemisphere and the southeast trade winds of the Southern Hemisphere.

Role in Indian Climate:

Some Famous Local Storms Of Hot Weather Season

During the hot weather season (March to May), several localized storms occur in different parts of India:

1. Loo:

2. Kalbaishakhi (Norwesters):**

  • Description: Localized thunderstorms that develop in the pre-monsoon season.
  • Occurs: In Bengal, Assam, and Odisha.
  • Characteristics: Characterized by violent winds, heavy downpour, hail, and lightning. Though destructive, the rain is beneficial for the tea and paddy crops.

3. Mango Showers:

  • Description: Pre-monsoon showers that occur in Kerala and Karnataka.
  • Occurs: Primarily in April and May.
  • Characteristics: These showers help in the ripening of mangoes and are beneficial for the tea and coffee plantations.

4. Blossom Showers:

  • Description: Showers that occur in Kerala and Karnataka, specifically beneficial for coffee plantations, promoting the blossoming of coffee flowers.
  • Occurs: Usually in March and April.

The Nature Of Indian Monsoon

The Indian monsoon is a complex and vital phenomenon that dictates the weather patterns and economic activities of the subcontinent. It is characterized by seasonal reversals of wind direction, bringing about distinct wet and dry periods.

Onset Of The Monsoon

The onset of the southwest monsoon is marked by a significant increase in rainfall activity. It is not a sudden event but rather a gradual progression.

Timing: Typically begins around the first week of June in the southernmost parts of India (Kerala).

Progression: It advances northwards and westwards, covering the entire country by mid-July.

Sudden Increase: Often, the onset is characterized by a sudden increase in rainfall, accompanied by strong winds and thunderstorms, known as the "burst" or "break" of the monsoon.

Influencing Factors: The onset is influenced by the northward shift of the ITCZ, the establishment of the easterly jet stream, and the pressure gradient between the subcontinent and the Indian Ocean.

Entry Of Monsoon Into India

The monsoon enters India in two branches:

1. The Arabian Sea Branch:

  • Path: This branch advances over the peninsula and moves towards the west coast of India.
  • Impact: It causes heavy rainfall on the windward side of the Western Ghats and the coastal plains. It then moves northwards over Gujarat, Rajasthan, and parts of the Ganga valley.
  • Directional Change: It is deflected by the Aravalli Range, causing less rainfall in Rajasthan. However, it ultimately merges with the Bay of Bengal branch over the northwestern parts of the Ganga valley.

2. The Bay of Bengal Branch:

  • Path: This branch first strikes the eastern coast of India.
  • Impact: It causes rainfall in the coastal regions of Odisha, Andhra Pradesh, and West Bengal.
  • Further Progression: It then moves inland into the Ganga valley and the northeastern parts of India.
  • Northeastern Influence: It is crucial for the heavy rainfall received in the northeastern states and the Himalayan foothills.

Rain-Bearing Systems And Rainfall Distribution

The rainfall in India during the monsoon season is primarily brought by:

1. Arabian Sea Branch:

  • Western Ghats: The orographic effect causes very heavy rainfall on the windward (western) side. The leeward (eastern) side receives much less rain.
  • Northern Plains: The branch moves inland, causing widespread rainfall in the plains.

2. Bay of Bengal Branch:

  • Eastern Coast: Causes rainfall along the eastern coast.
  • Northeastern India: Brings very heavy rainfall to the northeastern states.
  • Himalayan Foothills: Causes heavy rainfall along the foothills, influencing the development of the Ganga system.

Rainfall Distribution:

  • High Rainfall Areas: Western coasts, Western Ghats, northeastern states (>400 cm).
  • Moderate Rainfall Areas: Ganga valley, eastern India (100-200 cm).
  • Low Rainfall Areas: Parts of the Deccan Plateau, northwestern India (50-100 cm).
  • Very Low Rainfall Areas: Rajasthan desert (<50 cm).

Ei-Nino And The Indian Monsoon

El Niño: El Niño is a climate phenomenon that occurs irregularly (every 2 to 7 years) and involves the warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean. It is associated with changes in atmospheric pressure across the Pacific Ocean (the Southern Oscillation).

Impact on Indian Monsoon:

  • General Tendency: El Niño often has a negative impact on the Indian monsoon, leading to below-average rainfall (drought conditions).
  • Mechanism: The warming of the Pacific weakens the pressure gradient between the Indian Ocean and the Pacific Ocean, which in turn weakens the southwest monsoon winds. The northward shift of the ITCZ and the easterly jet stream may also be affected.
  • Variability: Not all El Niño events lead to a drought in India, and other factors also influence the monsoon. Similarly, La Niña (the opposite phenomenon of cooling Pacific temperatures) is often associated with stronger monsoons in India.
  • Research: The relationship between El Niño/La Niña and the Indian monsoon is a subject of ongoing scientific research.

Break In The Monsoon

Definition: A 'break' in the monsoon refers to a period during the monsoon season (June-September) when there is a significant reduction or cessation of rainfall in most parts of the country, particularly in the northern plains.

Causes:

  • Weakening of Monsoon Trough: The monsoon trough, a low-pressure line that draws monsoon winds, may become less active or shift northwards.
  • Influence of Western Disturbances: During breaks, western disturbances may become more active, drawing moisture away from the monsoon system.
  • Upper Air Circulation Changes: Changes in the position and strength of the ITCZ and the easterly jet stream can also contribute.

Impact:

  • Drought Conditions: Prolonged breaks can lead to drought-like conditions in rain-fed agriculture, impacting crops.
  • Regional Variation: While the northern plains may experience dry spells, the monsoon trough may remain active along the Himalayan foothills, leading to heavy rainfall in those regions, often causing floods.

The Rhythm Of Seasons

India's climate can be broadly classified into four distinct seasons, characterized by changes in temperature, rainfall, and wind patterns.

The Cold Weather Season

Period: December to February.

Characteristics:

  • Temperature: Clear skies, dry weather, low temperatures. Frost is common in northern plains. Pleasant days, cold nights.
  • Pressure & Winds: High pressure over northwestern India, cold dry winds blow from land to sea.
  • Rainfall: Little rainfall in plains. Snowfall in Himalayas. Light rainfall in Tamil Nadu due to Northeast monsoon.
  • Influences: Western disturbances bring light rain/snow to north and northwest.

The Hot Weather Season

Period: March to May.

Characteristics:

  • Temperature: Increasing temperatures across India. Hot dry winds ('Loo') in North India.
  • Pressure & Winds: Low pressure over northwestern India attracts winds from surrounding high-pressure areas.
  • Rainfall: Generally dry, but pre-monsoon showers ('mango showers', 'blossom showers') occur in south India. Localized thunderstorms are common.
  • Influences: Formation of low-pressure trough, northward shift of ITCZ.

The Southwest Monsoon Season

Period: June to September.

Characteristics:

  • Rainfall: Dominance of southwest monsoon winds bringing heavy rainfall to most of the country.
  • Onset: Starts around early June in Kerala and spreads across the country.
  • Pressure & Winds: Low pressure over North India draws moist winds from the Indian Ocean.
  • Influences: Arabian Sea and Bay of Bengal branches bring rain. Characterized by 'bursts' and 'breaks'.

Season Of Retreating Monsoon

Period: October to November.

Characteristics:

  • Withdrawal: Monsoon retreats from northern India by early September and from the rest of the country by mid-October.
  • Temperature: Clear skies, rising temperatures after withdrawal of monsoon.
  • Rainfall: Associated with the Northeast monsoon, causing rainfall in southeastern coastal areas (Tamil Nadu, southern AP).
  • Transition: A period of transition towards the cold weather season.

Traditional Indian Seasons

The traditional Indian calendar recognizes six seasons (Ritu), based on the Hindu lunar calendar and astronomical observations:

  • 1. Vasant (Spring): March-April
  • 2. Grishma (Summer): May-June
  • 3. Varsha (Monsoon): July-August
  • 4. Sharad (Autumn): September-October
  • 5. Hemant (Pre-winter): November-December
  • 6. Shishir (Winter): January-February

These seasons are closely linked to the agricultural cycle and cultural practices.

Distribution Of Rainfall

Rainfall distribution in India is highly uneven:

  • Heavy Rainfall Areas: Western coasts, Western Ghats, northeastern states (>400 cm).
  • Moderate Rainfall Areas: Ganga valley, eastern India (100-200 cm).
  • Low Rainfall Areas: Parts of Deccan Plateau, northwestern India (50-100 cm).
  • Very Low Rainfall Areas: Rajasthan desert (<50 cm).

Influenced by monsoons, relief features, and distance from the sea.

Variability Of Rainfall

Indian rainfall is highly variable, both spatially and temporally.

  • Spatial Variability: Differences in rainfall amounts across regions.
  • Temporal Variability: Variations in rainfall from year to year (e.g., El Niño effects), and within the season (breaks in monsoon).

  • Impact: Leads to floods and droughts, affecting agriculture and economy.

Climatic Regions Of India

Based on Köppen's classification and general climate characteristics, India can be divided into several climatic regions:

  • Tropical Humid Climate: Western coast, northeastern states (Af, Am, Cfa).
  • Tropical Dry Climate: Most of the peninsula, northern plains (Aw, Cwa).
  • Arid and Semi-arid Climate: Rajasthan, Gujarat (BWh, BSh).
  • Subtropical Humid Climate: Northern plains (Cwa).
  • Montane Climate: Himalayas (D type, E type, H).

Monsoons And The Economic Life In India

The monsoon is the backbone of India's economy:

  • Agriculture: Most crops depend on monsoon rains.
  • Hydropower: Rivers are harnessed for electricity, but flow varies with monsoon.
  • Water Supply: Crucial for drinking water, irrigation, and industrial use.
  • Transportation: Some rivers are navigable during monsoon.
  • Tourism: Monsoon season influences tourism in different regions.
  • Economic Vulnerability: Droughts or floods due to monsoon variability cause significant economic losses.

Global Warming

Global warming refers to the long-term heating of Earth's climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth's atmosphere.

Causes: The primary driver of global warming is the enhanced greenhouse effect caused by increased concentrations of greenhouse gases (GHGs) in the atmosphere.

Greenhouse Gases (GHGs)

Greenhouse gases are atmospheric gases that absorb and emit thermal infrared radiation. This process is the fundamental cause of the greenhouse effect.

Major Greenhouse Gases:

  • Carbon Dioxide (CO2): The most significant anthropogenic GHG, primarily released from burning fossil fuels (coal, oil, natural gas), deforestation, and industrial processes (like cement production).
  • Methane (CH4): Released from natural gas leaks, agriculture (livestock and rice paddies), and decomposition of organic waste in landfills. It is a more potent GHG than CO2 over shorter timescales.
  • Nitrous Oxide (N2O): Emitted from agricultural and industrial activities, as well as the combustion of fossil fuels and solid waste.
  • Fluorinated Gases (HFCs, PFCs, SF6, NF3): Synthetic gases used in various industrial applications (refrigerants, propellants). They are extremely potent GHGs, with very long atmospheric lifetimes.
  • Water Vapour (H2O): The most abundant GHG, but its concentration in the atmosphere is primarily controlled by temperature, creating a positive feedback loop. As the atmosphere warms, it can hold more water vapour, which further enhances warming.

The Greenhouse Effect:

The greenhouse effect is a natural process that warms the Earth's surface. When the Sun's energy reaches the Earth's atmosphere, some of it is reflected back to space, and the rest is absorbed and re-radiated by greenhouse gases. This absorbed energy warms the planet. Without this natural greenhouse effect, Earth would be too cold to support life.

Enhanced Greenhouse Effect: Human activities have significantly increased the concentration of GHGs in the atmosphere, trapping more heat and leading to global warming. This enhanced effect is causing changes in global climate patterns.

Impacts of Global Warming on India's Climate:

  • Changes in Monsoon Patterns: Increased variability, erratic onset and withdrawal, more intense rainfall events leading to floods, and prolonged dry spells causing droughts.
  • Rising Temperatures: Significant increase in average temperatures, leading to heatwaves.
  • Sea-Level Rise: Threatens coastal regions and islands with inundation and erosion.
  • Glacier Melt: Increased melting of Himalayan glaciers, impacting river flows in the long term.
  • Extreme Weather Events: Increased frequency and intensity of cyclones, heatwaves, and heavy rainfall events.