Changes and challenges: population pressure, exploitation, climate change, management strategies

Tropical Environments – Changes and Challenges (Cambridge AS & A Level Geography 9696)

1. Tropical Climates (Syllabus 7.1)

Tropical climates lie between 23.5° N and 23.5° S and are split into two principal types. The table adds the typical seasonal temperature range, which the syllabus expects.

• ITCZ (Inter‑tropical Convergence Zone): A low‑pressure belt where the trade winds converge. Its north‑south migration creates the wet season in both climate types.
• Monsoon systems: Seasonal reversal of winds caused by differential heating of land and sea (e.g., South‑Asian summer monsoon).
• Sub‑tropical anticyclones: High‑pressure cells that dominate the dry season of savannas, suppressing convection and producing prolonged drought.
• ENSO (El Niño‑Southern Oscillation): Warm (El Niño) or cool (La Niña) phases in the Pacific modify tropical rainfall; El Niño often reduces Amazon precipitation, raising fire risk.

2. Processes & Landforms (Syllabus 7.2)

2.1 Dominant Weathering Processes

• Chemical weathering – hydrolysis, oxidation, carbonation, solution: Accelerated by high temperature and moisture. Example: feldspar + H₂O → kaolinite + silicic acid.
• Physical weathering – thermal expansion, exfoliation, root wedging: Important on exposed rock faces and in areas with marked diurnal temperature changes.
• Biological weathering – organic acids from litter and roots: Enhances mineral dissolution and contributes to laterite formation.

2.2 Mass‑Movement Processes (required by the syllabus)

• Landslides (rock and soil): Triggered by intense rainfall, seismic activity, or rapid removal of vegetation.
• Debris flows and mud‑flows: Common on steep tropical slopes after prolonged wet periods; transport large volumes of sediment downstream.
• Soil creep: Slow, continuous downslope movement of weathered material, often enhanced by root growth and wet‑dry cycles.
• Rockfalls: Result from under‑cutting of cliffs by weathering or river erosion.

2.3 Characteristic Tropical Landforms

• Inselbergs (bornhardts, kopjes, tors): Rounded granite outcrops formed by deep chemical weathering and subsequent erosion of the surrounding softer material.
• Lateritic soils and ironstone plateaux: Result from intense leaching of silica, leaving iron‑ and aluminium‑rich residues.
• Karst topography (limestone): Sinkholes, caves and tower karsts (e.g., Guilin, China) produced by solution weathering in humid tropical climates.
• Alluvial floodplains and deltas: Built by high river discharge; support intensive agriculture (e.g., Mekong Delta).
• Mass‑movement landforms: Landslide scarps, debris‑flow fans, and soil‑creep terraces on steep slopes.

3. Tropical Vegetation, Soils & Ecosystems (Syllabus 7.3)

4. Changes & Challenges (Syllabus 7.4)

4.1 Population Pressure

• Growth rates in many tropical nations exceed 2 % yr⁻¹ → population doubles in ≈ 35 years (Rule of 70).
• Consequences: rapid expansion of informal settlements, higher demand for food, water, energy and land.

4.2 Exploitation of Natural Resources

• Timber: Selective logging, illegal extraction for furniture and paper.
• Minerals: Bauxite (Guinea), copper (DRC), gold (Ghana) – often open‑pit mining.
• Oil & gas: Offshore blocks in West Africa, on‑shore fields in Indonesia.
• Freshwater: Large‑scale irrigation (e.g., Brazil’s São Francisco River scheme).
• Biodiversity products: Non‑timber forest products, wildlife trade, ecotourism.

4.3 Climate‑Change Impacts

• Rising temperatures → higher evapotranspiration, altered seasonality.
• More intense cyclones, floods and droughts (e.g., 2020 Cyclone Amphan, Bay of Bengal).
• Sea‑level rise threatens mangroves and low‑lying islands (e.g., Maldives, Bangladesh delta).
• Coral bleaching in the Great Barrier Reef and Caribbean reefs.
• Shifts in agro‑ecological zones – staple crops such as rice and maize become less reliable in marginal areas.

4.4 Contrasting Country Examples (required by the syllabus)

• Low‑income tropical country – Bangladesh: High population density, frequent river flooding, rapid conversion of floodplains to rice paddies, and severe vulnerability to sea‑level rise.
• High‑income tropical country – Singapore: Small land area, intensive urbanisation, reliance on imported food, advanced water‑recycling (NEWater) and strict environmental regulations; serves as a contrast in how wealth influences management capacity.

4.5 Detailed Case Study with Prediction/Forecasting – Deforestation in the Brazilian Amazon (2019‑2024)

Background (2019‑2022): Approximately 1.2 million ha of forest were lost, driven by cattle ranching, soy expansion and illegal logging. Policy relaxations and strong international commodity demand accelerated the trend.

Forecast (2023‑2030): Using the UN‑FAO deforestation model (trend = + 4 % yr⁻¹) and assuming no major policy shift, projected loss is ~1.0 million ha by 2030. Climate‑model outputs (CMIP6) suggest increased drought frequency, which could raise fire‑related loss by an additional 15 %.

Impacts:

• Loss of carbon storage → ≈ 2 Gt CO₂ yr⁻¹ released.
• Reduced regional rainfall due to diminished evapotranspiration, potentially lowering river discharge by 5‑10 %.
• Threats to Indigenous livelihoods and loss of biodiversity hotspots.

Management actions (2019‑2024):

• Expansion of protected areas – new Indigenous reserves now cover ~30 % of the basin.
• REDD+ pilot projects offering payments for avoided deforestation.
• Satellite‑based monitoring (INPE’s DETER & PRODES) with rapid‑response enforcement teams.

Evaluation:

• Successes: Satellite monitoring cut illegal clear‑cutting in some zones; Indigenous territories recorded < 5 % deforestation versus the national average of 12 %.
• Limitations: REDD+ financing is intermittent; political opposition weakens law enforcement; global commodity demand continues to outpace protection.
• Overall judgement: Management has produced localized reductions but has not reversed the basin‑wide upward trend. Sustainable outcomes require stronger governance, stable financing for payments‑for‑ecosystem‑services, and integration of supply‑chain standards.

5. Management Strategies (linked to the case study)

• Protected‑area networks: National parks, biosphere reserves and Indigenous lands; maintain ecological corridors for species migration.
• Sustainable land‑use planning: Agro‑forestry (shade‑grown cacao, mixed‑species plantations), contour farming, integrated pest management.
• Community‑based management: Co‑management agreements, benefit‑sharing from ecotourism, capacity‑building for local monitoring.
• Climate‑adaptation measures: Early‑warning systems for floods/cyclones, climate‑smart crop varieties (drought‑tolerant rice), flood‑plain zoning.
• International agreements & financing: REDD+, Paris Agreement NDCs, Global Environment Facility (GEF) grants, corporate zero‑deforestation commitments.

6. Summary Table – Challenges, Drivers & Management