(a) Draw an outline map of Africa. On the map, show and name (i) one area that receives rainfall in winter; (ii) the dominant air masses over Africa in July...

(a) Outline map of Africa

The sketch map below shows an outline of Africa with the three required features clearly marked and named: the two belts that receive rainfall in winter (Mediterranean north coast and the south-western Cape), the dominant maritime tropical (mT) South-West Monsoon air mass drawn northwards across the Equator in July, and the northernmost July position of the Inter-Tropical Convergence Zone (ITCZ) over the Sahel.

Key to the map

• (i) Winter-rainfall areas (shaded): the Mediterranean coastlands of the extreme north (Atlas region of Morocco, Algeria, Tunisia) and the south-western Cape of South Africa. Both have a Mediterranean climate with hot, dry summers and mild, wet winters.
• (ii) Dominant air mass in July: the moist maritime tropical (mT) South-West Monsoon (equatorial maritime air) is drawn from the South Atlantic north-eastwards across the Equator into West and Central Africa, bringing the summer rains. The hot, dry continental tropical (cT) air dominates the Sahara to the north of the ITCZ.
• (iii) Position of the ITCZ in July: it lies in its northernmost position, well north of the Equator over the Sahel and southern Sahara (about 20°N).

(b) Effects of altitude on the climate of Africa

Altitude (height above sea level) strongly modifies the climate that latitude alone would produce, so that even places on the Equator can be cool. Its main effects are:

1. Temperature falls with height. Temperature decreases at an average rate of about \(6.5^{\circ}\text{C}\) for every \(1000\ \text{m}\) of ascent (the environmental lapse rate). Highland areas such as the Ethiopian Highlands, the Jos Plateau and the Kenya Highlands are therefore markedly cooler than the surrounding lowlands even though they lie near the Equator.
2. Cooler, temperate-like highland climates. Because of this cooling, equatorial highlands enjoy a pleasant, temperate-type climate that has attracted dense settlement and farming (for example the Kenya Highlands and the Jos Plateau).
3. Snow and ice on high peaks. The temperature drop is so great on the highest mountains that Kilimanjaro and Mount Kenya carry permanent snow and ice caps despite standing almost on the Equator.
4. Thinner air causes rapid heat loss. At high altitude the air is thin and contains less dust and water vapour, so it holds little heat and allows the ground's heat to escape (radiate) rapidly, especially at night. This gives large diurnal temperature ranges and cool nights on plateaux such as Jos.
5. Relief (orographic) rainfall. Highlands force moist air to rise, cool and condense, giving heavy relief rainfall on the windward slopes, while the leeward slopes lie in a dry rain-shadow with scanty rainfall.
6. Illustrative comparison. Nairobi and Mombasa lie on almost the same latitude, yet Nairobi, standing high on the plateau at about \(1675\ \text{m}\), has a much lower mean annual temperature than the coastal city of Mombasa near sea level. Using the lapse rate, the altitude difference alone accounts for a cooling of roughly \(\frac{1675}{1000}\times 6.5 \approx 10.9^{\circ}\text{C}\), confirming that altitude, not latitude, explains the contrast.