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S.3 Geography Notes

Semi-arid climate and Tropical Desert climate

Semi-arid climate:

This climate covers a broad belt of land across the northern Africa and a smaller zone in southern Africa.

It occurs between savanna climate zones and the true deserts.

  • There is an intense dry hot season from November to March.The rainy season is from April to August with a marked minimum in June and marked peaks in May and July. December and January are the driest months.
  • Rainfall is less than 550mm and unreliable throughout the year.
  • The passage of inter – tropical convergence zone northwards and the onset of the south east monsoon in April – May, accounts for the one peak of rainfall.
  • Temperatures are very hot throughout the year and the average temperature range from 280c-35oc.
  • There is very high diurnal range of temperature between 17oc-220c.
  • There is very Low humidity of about 20% or less.
  • There is limited cloud cover that is they are generally clear skies partly due to the limited atmospheric moisture required for cloud formation.

Economic activities: because of the harsh conditions of hot weather and semi-arid conditions little agriculture is carried out. Others are Tourism, hunting, Conservation of wildlife and Pastoralism


Tropical Desert climate:


They occur on the western side of Africa extending into the interiors, where the trade winds

originate from over the land, blowing to the oceans.

The aridity of the hot deserts is mainly due to the effects of the off-shore trade winds; hence they are also called the Trade Wind Deserts.

The tropical deserts are

  • Sahara Desert which extends from Senegal to Egypt and it is the largest single stretch of the desert, Namibia and Kalahari Deserts.

They are characterized by:

  • The rainfall is generally less than 250 mm per year, scarce and unreliable.
  • Rain normally occurs as violet thunderstorms of convectional type and may evaporate as soon as it stops raining.
  • It falls suddenly and pours continuously for a few hours over small areas.
  • The temperatures are extremely hot over 350c throughout the year.
  • Days are unbearably hot and the nights are cold which brings about high daily temperature ranges
  • Humidity is low

Study the table below showing the climatic characteristics of the different stations and answer the questions that follow:

Question: Draw suitable graph to represent the above information for Mali

Economic activities: tourism, nomadic pastoralism [Tuaregs of the Sahara Desert], sand quarrying, research and experiments in solar power development, hunting, irrigation farming in Egypt, Chad and Senegal; mining of minerals for example diamonds and copper in Kalahari and oil in Algeria.


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