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The interactive map below shows how the rainfall varies as you move
from equatorial West Africa (near Douala) to the influence of subtropical
high pressure under the descending air of the Hadley Cell (see Timbuktu
graph). The seasonal movement of the Inter Tropical Convergence Zone (ITCZ)
is responsible for the gradation in climate from north to south over the
area shown.
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Two things change closer to the equator - (i) the rainfall is generally
more in total and (ii) it is more evenly distributed through the year -
although local factors may complicate the simple pattern (as shown in these
graphs). This has an influence on natural ecosystem types with tropical
forests the natural biome near the equator but tropical grasslands (savanna)
dominating as the rain becomes more seasonal. Human landuse varies with
the climatic constraints and opportunities as shown in the figures for
agricultural productivity (below). In the table, cattle and sheep are typical
"dry land" produce, grain thrives in the seasonal savanna; rainfalls and
fruit trees require higher more consistent rainfalls or alternative irrigated
water supplies.
| 1996-7 figures | Mali (savanna and desert) | Burkina Faso (savanna) | Ghana (savanna and tropical forest) | Cameroon (tropical forest and savanna) |
| Grain production per person (kg/yr) | 224 | 232 | 101 | 92 |
| Fruit/capita (kg) | 5 | 7 | 99 | 151 |
| Cattle per 1000 people | 571 | 395 | 67 | 338 |
| Sheep per 1000 people | 543 | 527 | 133 | 262 |
Overview of agriculture in the region
Mali:
Land use: arable land 2%; permanent crops 0%; permanent pastures 25%;
forests and woodland 6%; other (including rough grazing) 67% (1993 estimate).
Irrigated land: 780 sq km (1993 estimate). Agriculture - products: cotton,
millet, rice, corn, vegetables, peanuts; cattle, sheep, goats.
Burkina Faso
Land use: arable land 13%; permanent crops 0%; permanent pastures 22%;
forests and woodland 50%; other (including rough grazing) 15% (1993 estimate).
Irrigated land: 200 sq km (1993 estimate). Agriculture - products: peanuts,
shea nuts, sesame, cotton, sorghum, millet, corn, rice, cattle.
Ghana
Land use: arable land 12%; permanent crops 7%; permanent pastures 22%;
forests and woodland 35%; other (including rough grazing) 24% (1993 estimate).
Irrigated land: 60 sq km (1993 estimate). Agriculture - products: cocoa,
rice, coffee, cassava (tapioca), peanuts, corn, shea nuts, bananas, timber.
Cameroon
Land use: arable land 13%; permanent crops 2%; permanent pastures 4%;
forests and woodland 78%; other (including rough grazing) 3% (1993 estimate).
Irrigated land: 210 sq km (1993 estimate) Agriculture - products: coffee,
cocoa, cotton, rubber, bananas, oilseed, wheat, root starches; cattle,
timber.
Summary table - agricultural production and climatic zones
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The table (left) shows how the spectrum of crop choices
reflects the nature of the climate. There are overlaps for several reasons:
(i) crop choice can depend on economic and political factors as much as
climatic, for example cotton has a better world market than millet even
if millet is a more reliable crop; (ii) countries may cross more than one
climate zone so Cameroon, for example, has wet climate in the south
but drier savanna in the north; (iii) local geography may influence agriculture
such that Mali's absence of rain is offset by the river Niger flowing through
the country, enabling rice to be grown.
These patterns are repeated in many other areas of the world where climatic gradients encourage gradual changes in landuse. Agriculture always seeks to maximise profits and one of the ways of doing this is to grow crops that are best suited to the local climate. Even in economically more developed countries like the United Kingdom, there is a clear gradient from predominantly mixed and dairy farming in the wetter western regions to predominantly arable farming in the drier east. |
Traditionally, most of the agriculture in the northern, more arid areas
of West Africa was based on a mixture of nomadic pastoralism and shifting
agriculture. Both these strategies involved dispersal of population pressures.
Unfortunately, political and economic changes have made traditional responses
to variable rainfall more difficult to implement. Increased nationalism
has made traditional tribal migration more difficult. The repayment demands
of international debt has meant many sub-Saharan countries have had to
restructure their agriculture. The emphasis has moved from subsistence
to profitability; thus the traditional range of crops grown has narrowed
to a smaller number of cash crops for the world markets. As the emphasis
has shifted from sustainability to profitability, many of the vulnerable
soils in the region have degraded. Poor soils result in increased vulnerability
to drought - there is less water stored in the soil so crop growth is hindered,
stream flow is reduced and recycling of water by evapotranspiration is
depressed. The control of soil erosion and desertification is all the more
urgent in the light of global warming models which predict these areas
will become both warmer and drier in a globally warmed world.
| Questions to consider:
Which human and economic factors compete with climate and soils to determine patterns of farming and landuse? If global warming gave drier conditions to these parts, describe the change in farming and landuse patterns you would expect to see in each of the countries in the table above. |
| Links within GIP:
Climate and people Tropical forests Amazonia case study |
External links: |
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