GS Notes

1.5 - Geography Notes 29

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Elaborate Notes

Climatic Regions: A General Classification

The classification of world climatic regions is a method of organizing and understanding the Earth’s diverse weather patterns. Geographers and climatologists have proposed various schemes, with the most widely recognized being the Köppen-Geiger classification system, first published by Wladimir Köppen in 1884 and later modified. The summary provided outlines a simplified, latitude-based classification which serves as a foundational framework.

  • 0° to 10° (Hot-Wet Equatorial Zone): This belt is dominated by the year-round influence of the Inter-Tropical Convergence Zone (ITCZ), leading to consistent high temperatures and heavy convectional rainfall.
  • 10° to 30° (Hot Zone): This zone experiences a transition. Its climates are largely influenced by the seasonal migration of the ITCZ and the dominance of the Sub-Tropical High-Pressure Belts. This results in distinct wet and dry seasons, leading to diverse climates like Monsoon on the eastern margins, Savanna (Sudan-type) in the continental interiors, and Deserts on the western margins.
  • 30° to 45° (Warm Temperate Zone): This mid-latitude zone is characterized by the seasonal interaction between tropical and polar air masses. The shifting of pressure and wind belts (especially the Westerlies) is a key determinant, creating climates like the Mediterranean on western margins (wet winters, dry summers), Steppe in continental interiors (semi-arid), and China-type on eastern margins (humid with year-round rain).
  • 45° to 60° (Cool Temperate Zone): Located in higher mid-latitudes, this zone is predominantly under the influence of the Westerlies and the Polar front, leading to frequent cyclonic activity. It includes the British-type on western margins (mild, wet), Siberian-type in continental interiors (extreme temperature range), and Laurentian-type on eastern margins (cold winters, warm summers, year-round precipitation).
  • 66.5° and above (Arctic/Polar Zone): Dominated by the Polar High, these regions experience extremely low temperatures, minimal precipitation (mostly as snow), and long periods of darkness and daylight. This is also known as the Tundra climate.

Hot and Wet Equatorial Climate

  • Distribution: Found typically between 5° N and 5° S of the Equator. Key regions include the Amazon Basin in South America, the Congo Basin in Africa, and the islands of the East Indies (Indonesia, Malaysia, Singapore, Papua New Guinea).
  • Temperature: Characterised by uniform high temperatures throughout the year. The annual average temperature is around 27°C. The diurnal (daily) range of temperature (around 8-10°C) is significantly greater than the annual range of temperature (less than 3°C). This uniformity led British geographer P.R. Crowe in his work ‘Concepts in Climatology’ (1971) to describe the climate as having “no seasons, but rather an eternal summer.”
  • Precipitation: Rainfall is heavy, typically exceeding 200 cm, and distributed evenly throughout the year. The primary mechanism is convectional rainfall. Intense solar heating (insolation) heats the ground, causing the moist air above it to rise, cool, condense, and form dense cumulonimbus clouds, resulting in heavy downpours, often accompanied by thunder and lightning, usually in the afternoons. This is often referred to as ‘4 o’clock showers’.
  • Vegetation: The constant heat and high rainfall support a lush, dense vegetation known as the Tropical Rainforest or ‘Selvas’ in the Amazon.
    • Evergreen Nature: Trees do not shed their leaves in any particular season, so the forest appears green year-round.
    • Layered Structure (Stratification): Competition for sunlight leads to a distinct vertical arrangement: a tall emergent layer, a continuous canopy layer, an understorey, and a shrub layer. The forest floor is often dark and clear of much undergrowth due to sunlight being the primary limiting factor.
    • Biodiversity: These rainforests are the most biodiverse terrestrial ecosystems on Earth, housing millions of species of flora and fauna. Early naturalists like Alfred Russel Wallace, co-developer of the theory of evolution, conducted extensive research in the Malay Archipelago (1854-1862), documenting this incredible diversity.
  • Human Life: Historically, these regions were sparsely populated by indigenous peoples engaged in shifting cultivation (e.g., ‘Jhum’ in India, ‘Ladang’ in Malaysia) or hunting and gathering. The hot, humid conditions and prevalence of diseases posed significant challenges to settlement.

Monsoon Type of Climate

  • Distribution: Best developed over the Indian subcontinent, Myanmar, Thailand, Laos, Cambodia, parts of Vietnam, and Southern China. It also extends to Northern Australia and parts of Eastern Africa.
  • Defining Characteristic: The most prominent feature is the seasonal reversal of winds, a concept first documented by Arab traders navigating the Indian Ocean.
    • Summer: Intense heating of the landmass (especially the Tibetan Plateau) creates a strong low-pressure system. This draws in moist, oceanic winds (South-West Monsoon in India) from the high-pressure area over the sea, leading to heavy rainfall.
    • Winter: The landmass cools rapidly, creating a high-pressure system, while the oceans remain relatively warm (low pressure). This causes a reversal of winds, which are now dry and blow from land to sea (North-East Monsoon).
  • Precipitation: Rainfall is highly concentrated in the summer monsoon season (3-4 months), followed by a distinct long dry season. Annual rainfall is variable, generally between 100 cm and 250 cm, but can be extreme in places like Mawsynram, India, as documented by the India Meteorological Department.
  • Vegetation: The seasonal drought necessitates adaptation. The natural vegetation is tropical deciduous forest. Trees like Teak, Sal, and Sandalwood shed their leaves during the dry winter season to conserve moisture.
  • Tropical Marine Climate: A sub-type found in regions like Central America, West Indies, and SE Brazil. These areas experience onshore trade winds throughout the year, modified by their passage over warm ocean waters. This results in more evenly distributed rainfall without a pronounced dry season, supporting a more rainforest-like vegetation.

Sudan Type of Climate (Tropical Savanna)

  • Distribution: This is a transitional climate found between the equatorial rainforests and the hot deserts, roughly between 10° and 20° N and S. It is named after the Sudan region in Africa, where it is most extensive. It is also found in the Llanos of the Orinoco basin (Venezuela) and the Campos of the Brazilian Highlands in South America, and in Northern Australia.
  • Climate: Characterised by a distinct wet and dry season.
    • Summers (Wet Season): The sun is overhead, and the ITCZ moves into the region, bringing convectional rainfall.
    • Winters (Dry Season): The ITCZ moves away, and the region comes under the influence of the dry, trade winds blowing from the subtropical high-pressure belts.
  • Precipitation: The average annual rainfall is moderate, around 70-100 cm, but is less reliable than in monsoon regions. The length of the wet season decreases with distance from the equator.
  • Vegetation: The landscape is known as tropical grassland or ‘parkland,’ featuring tall, coarse grass (like elephant grass) and scattered, drought-resistant, flat-topped trees like Acacia and Baobab. Trees are often pyrophytic (fire-resistant). The appearance changes drastically from a green landscape in summer to a dry, brown one in winter.
  • Human Life: This climate is often called the ‘Big Game Country’ due to the large populations of herbivorous and carnivorous animals. It has historically supported pastoralist communities. However, regions like the African Sahel on the southern fringe of the Sahara are highly vulnerable to desertification, a process exacerbated by overgrazing, deforestation, and climate change.

Desert Type of Climate

  • Distribution: Primarily located on the western margins of continents in the trade wind belt, roughly between 15° and 30° N and S. Examples include the Sahara and Kalahari in Africa; Atacama in South America; Mojave and Sonoran in North America; and the Great Australian Desert.
  • Causes of Aridity:
    1. Sub-tropical High-Pressure Belt: These regions are located under the descending, stable air of the subtropical highs, which inhibits cloud formation and precipitation.
    2. Offshore Trade Winds: The prevailing winds in these latitudes are the Trade Winds, which blow from east to west. On the western margins, these winds are blowing offshore (from land to sea) and are therefore dry.
    3. Cold Ocean Currents: The presence of cold currents (e.g., Canary Current for the Sahara, Benguela Current for the Namib, Humboldt/Peruvian Current for the Atacama) on the west coasts chills the air above them, increasing its stability and creating atmospheric inversion, which prevents rainfall.
  • Temperature: Deserts experience the highest diurnal range of temperature on Earth. Clear skies and low humidity allow for rapid heating by day (can exceed 45°C) and rapid cooling by night (can drop below 10°C).
  • Precipitation: Rainfall is scarce and unreliable, typically less than 25 cm annually.
  • Vegetation: Plants are adapted to extreme drought and are known as xerophytes. They have features like long roots, waxy cuticles, thorns instead of leaves, and fleshy stems to store water (e.g., Cacti, Date Palms, Acacia).

Mediterranean Type of Climate

  • Distribution: Found on the western margins of continents between 30° and 45° N and S. The type region is the lands bordering the Mediterranean Sea. Other locations include California (USA), Central Chile, the Cape Town region of South Africa, and southwestern and southern Australia.
  • Climate: Its defining feature is a concentration of rainfall in the winter and a distinct dry summer. This pattern is unique among all climatic types.
    • Summer: The region comes under the influence of the stable, subtropical high-pressure belt which shifts poleward with the sun. This brings dry, offshore trade winds, resulting in a hot, dry summer.
    • Winter: The subtropical high shifts equatorward, allowing the belt of the rain-bearing Westerlies and their associated temperate cyclones (depressions) to move into the region, causing moderate rainfall.
  • Temperature: Summers are hot and sunny, while winters are mild and wet. The climate is generally pleasant.
  • Vegetation: The natural vegetation consists of drought-resistant evergreen shrubs and small trees, collectively known as ‘Maquis’ or ‘Garrigue’ in Europe. Plants are sclerophyllous (hard-leaved) and include species like olive, cork oak, citrus fruits, and grapevines. This climate is ideal for viticulture (wine production).
  • Historical Significance: Scholars like Ellsworth Huntington in his work ‘Civilization and Climate’ (1915) argued, albeit from a now-criticized environmental determinist perspective, that this favorable climate contributed significantly to the rise of early civilizations in Greece and Rome.

Steppe Type of Climate

  • Distribution: Found in the continental interiors of the mid-latitudes, often in the rain shadow of high mountains. These temperate grasslands are known by various local names: the Steppes (Eurasia), Prairies (North America), Pampas (South America), Velds (South Africa), and Downs (Australia).
  • Climate: Characterised by continentality, leading to a large annual range of temperature with warm to hot summers and cold winters.
  • Precipitation: Rainfall is moderate, typically between 25 cm and 75 cm. It is higher than in hot grasslands (Savanna). Summer rainfall is largely convectional, while winter precipitation, often as snow, is associated with temperate cyclones (depressions) that penetrate the continents.
  • Vegetation and Soils: The dominant vegetation is short, nutritious grass. The lack of leaching and the decomposition of grass roots over millennia have produced some of the world’s most fertile soils, such as the ‘Chernozems’ (black earth) of the Eurasian Steppe and the ‘Mollisols’ of the American Prairies.
  • Economic Activity: These regions are known as the ‘breadbaskets of the world’ due to extensive, mechanized commercial grain farming (especially wheat). Animal rearing, particularly cattle ranching, is also a major economic activity.

China Type of Climate

  • Distribution: Found on the eastern margins of continents in the warm temperate latitudes (30°-45° N and S). Key areas are Southeastern USA, Southern China, Southeastern Brazil/Uruguay, Southeastern South Africa, and Southeastern Australia.
  • Climate: This climate is a modified version of the monsoon type. It experiences rainfall throughout the year, with a peak in summer.
    • Summer: The region is influenced by moist, onshore winds from the western side of the subtropical anticyclones, leading to convectional rain. It is also susceptible to tropical cyclones (hurricanes in the USA, typhoons in China).
    • Winter: Rainfall is derived from frontal depressions (temperate cyclones) that move along the polar front.
  • Temperature: Summers are warm to hot, and winters are mild, with occasional cold spells from the intrusion of polar air masses.
  • Vegetation: The uniform distribution of rainfall and warmth supports a luxurious and diverse vegetation, including both evergreen broad-leaved forests and deciduous trees. Important economic species include bamboo, palm, and in the USA, corn, cotton, and tobacco are extensively cultivated.

Laurentian Type of Climate

  • Distribution: Found on the eastern margins of continents in the cool temperate latitudes (45°-60° N and S). It is located poleward of the China type. Key regions include Eastern Canada (around the St. Lawrence River, hence the name), Northeastern USA (New England states), Northern China, Korea, and Northern Japan.
  • Climate: This is an intermediate climate between the British and Siberian types, having features of both maritime and continental climates. It experiences cold winters and warm summers.
  • Precipitation: Rainfall is distributed fairly evenly throughout the year, with a slight summer maximum. Both temperate cyclones and summer convection contribute to precipitation. A key feature, especially in North America and Japan, is the meeting of cold and warm ocean currents (e.g., cold Labrador Current meets warm Gulf Stream off Newfoundland). This creates dense fog and promotes plankton growth, leading to some of the world’s richest fishing grounds (e.g., the Grand Banks).
  • Vegetation: The natural vegetation is mixed forest. South of the 50°N parallel, deciduous forests with species like oak, maple, and birch are common. North of this, coniferous forests (part of the Taiga belt) dominate. Lumbering and the pulp and paper industry are major economic activities.

Prelims Pointers

  • Equatorial Climate:
    • Latitude: 0° - 10° N and S.
    • Temperature: Average 27°C; Diurnal range (8-10°C) > Annual range (<3°C).
    • Rainfall: >200 cm, convectional, year-round.
    • Vegetation: Tropical Rainforest (Selvas). Key features: Evergreen, high biodiversity, stratification.
    • Regions: Amazon Basin, Congo Basin, Malaysia, Indonesia.
  • Monsoon Climate:
    • Key feature: Seasonal reversal of winds.
    • Rainfall: Concentrated in summer; distinct dry season.
    • Vegetation: Tropical Deciduous forests (e.g., Teak, Sal).
    • Regions: India, Pakistan, Bangladesh, Indo-China, N. Australia.
    • Sub-type: Tropical Marine Climate (e.g., Central America) has rain throughout the year from onshore trade winds.
  • Sudan (Savanna) Climate:
    • Latitude: 10° - 20° N and S.
    • Climate: Hot, wet summers and cool, dry winters.
    • Rainfall: 70-100 cm, mainly convectional in summer.
    • Vegetation: Tropical grasslands with scattered trees (Parkland landscape).
    • Local Names for Grasslands: Llanos (Venezuela), Campos (Brazil).
  • Desert Climate:
    • Latitude: 15° - 30° N and S, on western margins.
    • Causes: Subtropical High Pressure, Offshore Trade Winds, Cold Ocean Currents (e.g., Humboldt, Benguela, Canary).
    • Rainfall: < 25 cm per annum.
    • Temperature: High diurnal range.
    • Vegetation: Xerophytic (e.g., Cactus, Date Palm).
    • Major Deserts: Sahara, Atacama, Namib, Kalahari, Great Australian Desert.
  • Mediterranean Climate:
    • Latitude: 30° - 45° N and S, on western margins.
    • Key Feature: Dry, hot summers and wet, mild winters.
    • Cause of winter rain: Onshore Westerlies and temperate cyclones.
    • Vegetation: Sclerophyllous shrubs (Maquis/Garrigue), citrus fruits, olives, grapes.
    • Regions: California, Central Chile, Cape Town area, SW & S Australia.
  • Steppe (Temperate Grassland) Climate:
    • Location: Continental interiors in mid-latitudes.
    • Climate: High annual range of temperature (continentality).
    • Soil: Fertile Chernozems (Black Earth) and Mollisols.
    • Economic Activity: Commercial grain cultivation (‘Breadbaskets of the world’).
    • Local Names: Prairies (N. America), Pampas (S. America), Velds (S. Africa), Downs (Australia), Steppes (Eurasia).
  • China Type Climate:
    • Latitude: 30° - 45° N and S, on eastern margins.
    • Rainfall: Throughout the year, summer maximum. Influenced by both tropical (typhoons) and temperate cyclones.
    • Vegetation: Mixed evergreen and deciduous forests.
    • Regions: SE USA, SE China, SE Brazil, SE Australia.
  • Laurentian Climate:
    • Latitude: 45° - 60° N and S, on eastern margins.
    • Climate: Cold winters, warm summers.
    • Key Feature: Convergence of cold and warm ocean currents (e.g., Labrador & Gulf Stream) causing fog and rich fishing grounds.
    • Vegetation: Mixed forest (Deciduous in the south, Coniferous in the north).
    • Regions: NE USA, Eastern Canada, N. Japan, N. China.

Mains Insights

GS Paper I (Geography & History)

  1. Climate as a Determinant of Human History and Society:

    • Mediterranean Climate: The mild, wet winters and dry summers were conducive to the development of early agrarian societies and classical civilizations like Greece and Rome. The focus on specific crops like olives and grapes shaped their economy and trade. However, avoid simplistic environmental determinism; climate is an influencing factor, not the sole cause.
    • Monsoon Climate: The rhythm of the monsoon has profoundly shaped the culture, agriculture, and economy of South Asia. The concept of monsoon as a ‘unifying bond’ for India is a key theme. The unreliability of monsoons (floods and droughts) is a persistent challenge influencing settlement patterns, food security, and government policy.
    • Steppe Climate: The vast Eurasian Steppe was the highway for nomadic empires (e.g., Mongols) whose pastoral lifestyle was perfectly adapted to the climate. The eventual conquest of these grasslands by sedentary agricultural empires (e.g., Russia, China) marked a major shift in world history.

  2. Climate and Economic Activities:

    • Cause-Effect Relationship: The specific climatic conditions directly enable certain primary economic activities. For instance, the year-round warmth and rainfall in equatorial regions are ideal for plantation crops like rubber and palm oil, while the fertile chernozem soils of the Steppes make them global ‘breadbaskets’ for wheat.
    • Comparative Analysis: Compare the agricultural practices in different climatic zones. For example, contrast the subsistence, shifting cultivation of rainforests with the extensive, mechanized commercial farming of the Prairies, and the intensive subsistence agriculture of Monsoon Asia. This reflects how climate, soil, population density, and technology interact to shape agricultural landscapes.

GS Paper III (Environment & Economy)

  1. Climate Change and Vulnerability:

    • Desertification: The Savanna (Sudan-type) and Steppe climates are highly vulnerable to desertification. The Sahel region in Africa serves as a critical case study where climate change, coupled with human pressures like overgrazing, is expanding the Sahara desert, leading to food insecurity, resource conflicts, and forced migration.
    • Threats to Biodiversity Hotspots: Equatorial rainforests, despite their resilience, are under severe threat from deforestation driven by logging, cattle ranching, and agriculture. Climate change further exacerbates this by altering rainfall patterns and increasing the frequency of droughts and fires, threatening global biodiversity.
    • Monsoon Variability: Climate change is predicted to make the Indian monsoon more erratic and intense. This has direct implications for India’s agrarian economy, water security (both floods and droughts), and the livelihoods of millions of farmers.

  2. Resource Management and Geopolitics:

    • Water Scarcity: In desert and semi-arid regions (Steppe, Mediterranean), water is a critical and often contested resource. Geopolitical tensions can arise over trans-boundary rivers like the Nile, Indus, and Jordan. Sustainable water management strategies are crucial for stability.
    • Food Security: The stability of global food supply is heavily dependent on the productivity of the ‘breadbasket’ regions (Steppes). Climate-induced disruptions in these areas can have ripple effects on global food prices and availability. Diversification of food sources and climate-resilient agriculture are key policy imperatives.
    • Conservation vs. Development: In regions like the Amazon and Congo basins, there is a constant tension between the need for economic development and the global imperative to conserve these vital carbon sinks and biodiversity hotspots. This involves complex negotiations over international funding, indigenous rights, and national sovereignty.

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