Note: This chapter was removed from the NCERT curriculum in the 2022 rationalization. Retained here as human-environment interaction in tropical regions — Amazon deforestation, Ganga basin ecology, and tropical agriculture — are relevant to UPSC GS1 and GS3 (Environment, Agriculture).

PART 1 — Quick Reference Tables

Amazon Basin vs Ganga-Brahmaputra Plains

Feature Amazon Basin Ganga-Brahmaputra Plains
Location South America (mainly Brazil) South Asia (India, Bangladesh, Nepal)
Climate Equatorial — hot, wet, year-round Tropical monsoon — hot, wet summers; dry cool winters
Vegetation Dense tropical rainforest Tropical moist deciduous; paddy fields; riverine forests
Land use Largely forest; deforestation for cattle/soy Intensively cultivated; rice, wheat, jute, sugarcane
Population Sparse in forest; cities on river banks One of world's most densely populated regions
Main rivers Amazon (2nd longest; highest discharge) Ganga, Yamuna, Brahmaputra, Ghaghra, Kosi
Major threats Deforestation, mining, dam building Floods, pollution, over-extraction of groundwater

PART 2 — Detailed Notes

The Amazon Rainforest — Life in a Tropical Rainforest

Explainer

Living in the Amazon:

The Amazon rainforest is home to hundreds of Indigenous peoples who have lived there for thousands of years, adapting perfectly to the environment.

Indigenous adaptations:

  • Shifting cultivation (slash-and-burn/swidden agriculture): Clear a small patch of forest → burn vegetation → plant crops → cultivate 2–3 years → move on → forest regenerates. Sustainable when population is low and forest is large; unsustainable with large population pressure
  • Houses: Built on stilts above the forest floor (floods, animals, insects); use local materials — palm thatch, hardwood poles
  • Food: Hunting (blowpipes, bows — tapir, deer, birds), fishing (piranha, arapaima — world's largest freshwater fish), gathering (fruits, nuts, roots), cultivation (manioc/cassava — staple; maize, sweet potato)
  • Medical knowledge: Amazonian peoples have profound knowledge of medicinal plants — source of 25% of pharmaceutical drugs in the West including quinine (malaria), curare (muscle relaxant used in surgery)

Amazon River:

  • 2nd longest river (6,400 km) after Nile; BUT largest by discharge volume (20% of all freshwater flowing into oceans)
  • Has ~3,000 species of fish (more than entire Atlantic Ocean)
  • River transportation is the primary means of getting around — roads are few
  • Cities: Manaus (Brazil) — large city in the middle of the Amazon; founded during the rubber boom (~1890s); famous rubber barons built the Teatro Amazonas opera house

Deforestation threats:

  • Brazil: Average annual deforestation: 10,000–15,000 km²/year (varies; Bolsonaro era saw spike; Lula era has reduced it)
  • Causes: Cattle ranching (~80% of deforestation), soy cultivation, logging, mining, hydroelectric dams
  • Tipping point concern: Scientists estimate Amazon may have a "tipping point" where enough deforestation causes the eastern Amazon to transform into savanna — losing moisture recycling function; estimated trigger at ~20–25% deforestation; currently ~17–20% lost
  • FUNAI: Brazil's National Indian Foundation — responsible for protecting indigenous peoples; their rights under threat from illegal settlers and agricultural interests

The Ganga-Brahmaputra Plains

UPSC Connect

UPSC GS1 — Ganga Plains Geography:

The plains: The Indo-Gangetic Plain extends from Punjab in the northwest to Assam in the northeast — one of the world's most fertile and densely populated regions, formed by alluvial deposits from the Himalayan rivers.

Agricultural base:

  • Green Revolution (1960s–70s): Punjab and Haryana — HYV wheat and paddy, chemical fertilisers, irrigation → transformed from deficit to surplus; India achieved food self-sufficiency
  • Major crops: Wheat (Punjab, UP, Bihar, Haryana), Rice (UP, Bihar, West Bengal, Assam), Jute (West Bengal — Ganga delta), Sugarcane (UP — largest in India)
  • Flood plains: Extraordinarily fertile; Ganga alluvial soil = khadar (newer, near river, very fertile) and bhangar (older, higher ground, slightly less fertile)

Major cities: Delhi, Agra, Varanasi, Allahabad (Prayagraj), Patna, Kolkata — nearly all major North Indian cities are on or near the Ganga-Yamuna system.

Brahmaputra basin:

  • The Brahmaputra flows from Tibet (as the Tsangpo) through Arunachal Pradesh and Assam
  • Flows through narrow valley between Himalayas and Shillong Plateau; one of the world's deepest river gorges (Yarlung Tsangpo Grand Canyon — deeper than Grand Canyon)
  • Assam: Tea plantations (Assam tea = most production in India), rice, flood-prone agriculture
  • Majuli Island: World's largest river island (Brahmaputra); cultural centre; facing erosion threat; area reduced from ~1,250 km² to ~500 km²
  • Brahmaputra carries enormous sediment → annual floods in Assam; over 100 rivers join it in Assam

Ganga Pollution and Action Plans:

  • Ganga Action Plan (GAP) 1985: First effort to clean Ganga; largely unsuccessful
  • Namami Gange Programme (2015): Rs 20,000 crore; sewage treatment, ghats, crematoria; modest improvements; NMCG (National Mission for Clean Ganga) implementing
  • Main sources of pollution: Untreated sewage (major cities), industrial effluents (tanneries in Kanpur, dyeing units), agricultural runoff, solid waste, religious offerings
  • Ganga declared National River of India (2008)

Human Adaptations to Tropical Environments

Explainer

How humans adapt to hot, wet tropical environments:

Architecture:

  • Sloped roofs (steep pitch → shed heavy rainfall quickly; prevents water pooling)
  • High ceilings (hot air rises; keeps living space cooler)
  • Open verandahs and courtyards (air circulation)
  • Elevation on stilts (above floods, away from ground moisture and insects)
  • Thick walls or bamboo walls with gaps (thermal regulation + air flow)

Agriculture in tropics:

  • Multiple cropping: Hot, wet climate allows 2–3 crops per year
  • Paddy cultivation: Wet rice farming perfectly suited to monsoon climates; flooded fields (paddies) actually conserve water
  • Plantation agriculture (colonial legacy): Tea (Assam, Kerala), rubber (Kerala), coffee (Karnataka), coconut (Kerala coastal) — introduced by British for export
  • Challenges: Soil leaching (heavy rainfall washes nutrients downward), pests, humidity (crops vulnerable to fungal diseases)

Health and tropical environment:

  • Vector-borne diseases are more prevalent in hot, wet climates: malaria (Anopheles mosquito), dengue (Aedes mosquito), Japanese encephalitis (rice-growing areas), kala-azar (sandfly)
  • India's public health challenge: burden of tropical diseases + nutrition deficiency + climate change increasing disease range

Exam Strategy

Prelims traps:

  • Amazon = 2nd longest river (after Nile) but largest by discharge/volume (more water than any river)
  • Amazonian indigenous peoples use blowpipes, shifting cultivation — NOT settled farmers
  • Deforestation main cause = cattle ranching (NOT logging, despite common assumption; logging is 2nd)
  • Ganga: khadar = newer alluvium (near river, very fertile); bhangar = older alluvium (higher ground)
  • Majuli = world's largest river island (Brahmaputra, Assam); facing erosion — area shrinking
  • Namami Gange = 2015 (NOT Ganga Action Plan which was 1985 — two different programs)
  • Green Revolution = Punjab and Haryana (wheat + paddy); NOT all of India simultaneously

Previous Year Questions

Prelims:

  1. "Khadar" and "Bhangar" are terms associated with which of the following?
    (a) Types of soil in the Deccan Plateau
    (b) Types of alluvial soil in the Ganga plains (newer and older alluvium)
    (c) Irrigation systems in Rajasthan
    (d) Forest types in the Western Ghats

  2. The world's largest river island, Majuli, is located in which river?
    (a) Ganga
    (b) Brahmaputra
    (c) Yamuna
    (d) Mahanadi

  3. "Namami Gange" programme, launched in 2015, is primarily concerned with:
    (a) Interlinking of rivers in North India
    (b) Cleaning and rejuvenating the Ganga river
    (c) Flood management along the Ganga
    (d) Construction of dams on the Ganga tributaries