Hot Deserts, Knowledge Organiser

Key Terms

• Arid: <250mm rainfall/year; evaporation > precipitation
• Diurnal temperature range: Day-night temperature difference (up to 50°C in deserts)
• Hadley Cell: Atmospheric circulation creating desert belts at 20–30° latitude
• Drought-adapted plants: Cacti, acacia
• Desert animal adaptations: Camel, fennec fox
• Stomata open at night only: Reduces water loss
• Ephemeral: Plant that exists as dormant seed; germinates rapidly after rain
• Desertification: Human-driven degradation of semi-arid land
• Salinisation: Salt build-up in irrigated soils — reduces fertility
• Pastoralism: Livestock herding across seasonal grazing routes

Key Facts and Statistics

• Sahara: 9.2 million km² (largest hot desert); Thar: ~200,000 km²
• Thar population: 83 million (most densely populated hot desert)
• Thar rainfall: 100–500mm/year; 325 days of sunshine
• Bhadla Solar Park: 2,245 MW — world's largest solar farm (2023)
• Indira Gandhi Canal: 649km, irrigates 2 million hectares
• Jaisalmer tourism: 1.5 million visitors (2019)
• Desertification: 12 million hectares lost/year globally; 2 billion people affected
• Stone bandi (Burkina Faso): 300,000 hectares restored; +50–80% crop yields
• FMNR (Niger): 5 million hectares, 200 million trees restored
• Great Green Wall: 8,000km target; 15 million hectares completed (15% of target)

Thar Desert Case Study

• Opportunities: Solar (Bhadla 2,245 MW); tourism (Jaisalmer 1.5m visitors); minerals (80% India's gypsum); irrigated farming (canal)
• Challenges: Water scarcity; 50°C+ summers; dust storms (100+ deaths 2018); inaccessibility; desertification pressure
• Canal costs: Salinisation; downstream water conflict; groundwater depletion; climate risk to Himalayan source

Exam Essentials

• Always name specific plants/animals with specific adaptations — not just "has small leaves"
• Desertification = human-driven degradation, NOT natural spread
• Use the 7-step cascade for 6-mark causation questions
• Balance opportunities AND costs for the Indira Gandhi Canal
• Compare solutions using evidence: stone bandi vs FMNR vs Great Green Wall
• CACTUS mnemonic: Climate, Adaptations, Challenges, Thar, Unsustainable pressures, Solutions

Common Mistakes

• Vague adaptations: Never write "plants have small leaves to save water" — name the plant (e.g. saguaro cactus), name the adaptation (stomata open only at night) and explain the mechanism
• Calling desertification natural: Desertification is human-accelerated land degradation — overgrazing, overcultivation and deforestation are the key drivers examiners expect, not just climate
• Ignoring the Thar case study: Always use the Thar Desert (India) for opportunities and challenges — vague answers without a located example lose marks
• Only listing problems for the Indira Gandhi Canal: Balance is essential — state the benefits (2 million hectares irrigated) AND the costs (salinisation, water conflict, groundwater depletion)

Memory Aid

Six letters for everything you need to know about hot deserts: LetterWhat It Stands ForKey Fact to Recall C Climate — arid conditions, extreme temperature range <250mm rain; 20°–30° latitude; diurnal range up to 50°C; Hadley Cell subsidence explains location A Adaptations: plants and animals with specific mechanisms Saguaro: pores open only at night + accordion stem; Camel: oval blood cells + 30% dehydration tolerance; Fennec fox: 15cm ears radiate heat; Ephemeral seeds: dormant for decades C Challenges — water, heat, dust, inaccessibility Thar: 50°C summer max; loo winds; wells drying up; 25% of India land degraded; dust storms killing 100+ in 2018 T Thar case study — opportunities for development Bhadla Solar Park: 2,245 MW (world's largest); Indira Gandhi Canal: 649km, 2m hectares irrigated; Jaisalmer tourism: 1.5m visitors; 80% of India's gypsum from Rajasthan U Unsustainable pressures — drivers of desertification 7-step cascade: population growth → overgrazing → over-cultivation → deforestation → climate change → soil erosion → desertification; 12 million hectares lost per year globally S Solutions — stone bandi, FMNR, Great Green Wall Stone bandi: 300,000 hectares, +50–80% crop yield (Burkina Faso); FMNR: 5m hectares, 200m trees (Niger); Great Green Wall: 8,000km, 15m hectares completed so far Bonus: Adaption Types in Three Words Plants: Store, Reduce, Reach (store water in stems / reduce surface area / reach deep groundwater) Animals: Avoid, Concentrate, Store (avoid heat through nocturnal behaviour / concentrate urine / store fat reserves)