Dr. Spring’s Lecture: Geography 2
The African farmer is affected by climate, vegetation and soils
Climate
• Similar climatic patterns north and south of the equator
• Equatorial, tropical wet and dry, desert, and Mediterranean climates
• Differ in terms temperature, rainfall, and evaporation.
Temperatures high throughout
• Mean annual temp. ranges from 15 to 33 C (59 to 91 F)
• Highest temp. not at the equator
– Continuous cloud cover and moisture protect against the sun's rays.
Temperatures
• Fairly constant at the equator
• Fluctuates farther north or south of equator daily and annually
Difference between means for the coolest and warmest months
• big difference in Algeria
• small difference in Congo
Day-time highs and night-time lows
• Algeria: large variation
• Congo: small variation
Rainfall distribution
• More critical than temperature ranges
• Explained by the Inter-tropical Convergence Zone
Inter-tropical Convergence Zone (I.T.C.Z.)
• Low pressure zone near equator
• Trade winds converge and accumulate, air ascends causing rain.
I.T.C.Z.
• Not stationary
• Oscillates between 20 degrees north and 25 degrees south.
• Irregular and unpredictable
Direct correlation between the I.T.C.Z. and rainfall patterns.
• January-- I.T.C.Z. rainfall at Equator and south
• July-- I.T.C.Z. shifts; rainfall is north of equator.
Only equatorial zone receives rain throughout the year
• Both rainbelts overlap
• About 8% of Africa, the Congo (Zaire)
• Basin and the coast of West Africa, receive >1600 mm of rain annually
50% of the continent is arid or semi-arid
• Agriculture is constrained by water availability in over half of Africa.
Africa has a negative water balance
• Evaporation> rainfall, leading to water deficits.
– Evaporation is high because of high temp. and radiation.
• Only Equatorial Africa has a water surplus.
I.T.C.Z. is important for the African farmer
• I.T.C.Z. causes distinct dry season except in equatorial areas
• Length of the dry season
– 3 - 8 months just North and South of Equator
– up to 8 - 10 months further away
Farming and food production
determined by
• Length of the dry relative to the wet season
Lengthy Dry Seasons
• Proper storage systems become part of the food production cycle
Rains a crucial period for the farmer
• Farming in a restricted rainy season
• Planting and weeding in a short period of time
• High labor demands
Local traditional varieties
• Are adapted to
– Rainfall conditions
– Plant diseases and pests
Local traditional varieties
• Evolved over thousands of years
• Some were domesticated in the area
Crops domesticated in West Africa
• millet
• sorghum
• okra
• watermelon
• fluted pumpkin
• kola (coca cola )
• cotton
• sesame
Crops domesticated in Ethiopia
• Coffee
• Teff
• Enset
• Cress
• Castor (castor oil)
Rainfall variability is high
• The smaller total amount, the higher the variability
Other factors in climate
• Warm or cold ocean currents
• High plateau of East Africa
• The Great Escarpments
• Cold fronts from Antarctica
• Thunderstorms in equatorial Africa
Regional distortions
• The Mediterranean climate
– Northern and Southern Africa
• The Sahara desert
– Brought about by dry air masses coming from Arabia
VEGETATION
• Correlates strongly with rainfall patterns
• Dry conditions -- desert-like vegetation
• Semi-arid conditions--steppe
VEGETATION
• Sub-humid conditions--savannas
• Wet conditions--forests and rainforests
Vegetation
• Continuum
rainforest-forest--savanna--steppe--desert
• No true boundaries exist
From the equator to the desert
• Fewer and smaller trees
• Increased grassland-like vegetation
• Decreased diversity of species
Vegetation zones resemble north and south of equator
• Rainforests cover only 8-10%
• Africa--continent of savannas and deserts
Rainforests
• Poor soils
• Nutrients recycled
Destruction of rainforests
• Rapid
• Large amounts cleared yearly
Savannas
• Between forests, steppes, and deserts
Nearer to the equator
• Trees dominate grasses
• Woodland savanna
Further north or south of the equator-- a distinct dry season
• Savanna grasslands
• Woodland savanna
Characteristics of savanna
• Herbivores (rhinoceros, elephants and giraffes) predators (lions)
Characteristics of
savanna areas
• Baobab trees (girths of 30 feet +)
• Huge bodies of granite
Steppe
• Transition zone between savannas and deserts
• Narrow bands on either side of the savanna.
Semi-arid conditions
e.g., Kalahari Desert
• Sparse vegetation
• Plants-- extremely scrubby
• Thorn trees
Under extreme conditions
• Cactus and aloe, growing in almost bare soils.
• Vegetation- a function of climate and soils.
Steppes: extensive livestock grazing
• Drier areas used by pastoralists
Agriculturalists occupy wetter areas
• Competition between the two groups for best land
Rainfall variability and drought
• High in the between savannas and deserts
• Above-average alternates with low rainfall
• Produces droughts
1970s: Sahel area (West Africa) 1980s: Ethiopia 1990s Southern Africa, Horn of Africa
• Massive crop failures
• Famine and starvation (people and livestock)
1/3 of Africa taken up by three main deserts
• Sahara, 1/4 of the land mass of the continent
• Namib
• Kalahari, a semi-arid region rather than true desert
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Desert proper
Areas receiving less than 250 mm
of rain per year
Little vegetation
Daily temp. fluctuate > 35 C (95 F)
Seasonal av. temp. > 40 C (104 F)