Climate and Natural Vegetation of East Africa

Introduction

In this chapter, you are going to learn about the different types of climate and natural vegetation in East Africa. You are going to learn how these two are natural resources that need to be appreciated and sustainably used for the benefit of the people of Uganda in all generations.

Activity 9.1
1. Explain what you understand by climate.
2. List any five climates you know.
3. Describe two of the climates listed above.
You have probably used words like hot, wet and dry to describe the two climates. Describing climate means pointing out its main characteristics. It is these characteristics that differentiate one climate from another. You are going to learn about the characteristics of the main climates in East Africa.

What are the Characteristics of the Main Types of Climate?
Learning about the characteristics of climates will help you to understand why each climate is different from other climates. This will enable you to understand why there are many types of climate in East Africa.

Equatorial Climate
This climate is found in areas that lie between 5°N and 5°S of the Equator. In East Africa, the Equatorial climate is experienced around the Lake Victoria basin, including the islands within the lake. To understand this better, do Activity 9.2.

Activity 9.2
In pairs or individually, study Figure 9.1 and do the following tasks:
1. Write down the months in which the highest amount of rainfall is received at Entebbe.

2. How many seasons of highest rainfall does Entebbe experience?
Why do you think the area experiences that number of seasons?
3. Is the relative humidity at Entebbe high or low? Give reasons to support your answer.
4. Calculate the annual range of temperature for Entebbe. Is the range high or low?
5. Calculate the total annual rainfall for Entebbe. Is the rainfall low, moderate, or heavy?

The climate of Entebbe is similar to that of other areas within the Lake Victoria region of East Africa. You have realised that areas with an Equatorial climate receive two peaks of heavy rainfall. This is called double maxima rainfall distribution. The climate of the Lake Victoria region is called Modified Equatorial climate. That means that this region receives heavier rainfall than other equatorial lands and does not have any month without rainfall.

Mountain or Montane Climate

This type of climate is mainly found in the highlands, especially in the mountains. Think of areas in East Africa which are likely to be having this type of climate. In these areas, temperatures are generally low and air pressure decreases with altitude. Areas with the montane climate receive mainly relief rainfall, which is heavier on the windward side. The leeward side receives very little rainfall. Why do you think this is so? The condition you have explained is called the rain shadow effect.  To understand the characteristics of Mountain climate, study Figure 9.2

Activity 9.3

Study Figure 9.2 and do the following tasks:
1. Which months have the highest rainfall?
2. Which months have the lowest rainfall?
3. Describe rainfall distribution in Nairobi.
4. Which are the hottest months?
5. Which months have the lowest temperatures?
6. Calculate the total rainfall for Nairobi.

7. Copy the graph into your notebook.

Semi-arid and Arid Climate

Activity 9.4
In groups, study Figure 9.3 and do the following:
1. Copy the figure into your notebooks.
2. Find out the months with the heaviest rainfall.
3. Which months have the lowest rainfall?
4. Describe the characteristics of the climate of the area represented by Figure 9.3.
5. Suggest the likely economic activities carried out by the people living in the area represented by the graph. Give reasons for each activity you suggest.

This type of climate is found in northern and north-eastern Kenya, e.g. the Chalbi Desert, Karamoja in north-eastern Uganda, Nyiri desert in southern Kenya, in central Tanzania, and in north-eastern parts of Tanzania, e.g. the Masai steppe. It is also experienced in the Ankole-Masaka corridor in Uganda. Areas in the Western Rift Valley region around Lake George and Lake Edward also experience a semi-desert climate.

Tropical or Savannah Climate

This type of climate covers the greatest part of East Africa. It is found next to the equatorial region, both north and south of the equator. It may not differ much from the equatorial climate. Generally, Savannah lands receive less rainfall than places in the Equatorial climate region. Also, they have well-marked rainy and dry seasons. You can understand the other characteristics of the Savannah climate by studying Figure 9.4.

The Coastal Tropical Climate

This type of climate is experienced in the coastal region of East Africa in places like Malindi, Mombasa, Tanga and Dar es Salaam. The climate is modified by the Southeast Trade Winds and the sea. The rainfall is heavy and well distributed throughout the year and ranges between 1,000 mm and 1,800 mm. The area experiences high temperatures throughout the year. Why do you think temperatures are hot in this region? Figure 9.5 is a climate graph of Mombasa, an area with a coastal tropical climate.

What Factors Influence Climate in East Africa?
In Chapter Five, you learnt about the revolution of the earth while in Chapter Seven you learnt about the relief of East Africa. Now you are going to learn how these and other factors affect the climate of East Africa, including that of your home area.

Activity 9.5
In pairs or groups, use your knowledge of the movements of the earth to do the following tasks:
1. When is the sun overhead at the equator?
2. Explain what happens in the region close to the equator when the sun is overhead at the equator.
3. Why does the region close to the equator receive two peaks of rainfall?
4. When is the sun overhead at the Tropic of Cancer?

5. When do areas close to the Tropic of Cancer receive rain and why?
6. When is the sun overhead at the Tropic of Capricorn?
7. When do areas close to the Tropic of Capricorn receive rainfall and why?
8. Share what you have written through a whole class discussion.

The Inter Tropical Convergence Zone (ITCZ)

The overhead sun causes much heating of the ground. This in turn causes a low pressure zone which attracts winds from high pressure zones. The low pressure zone within the tropics in which the winds from the northern and southern hemispheres meet is called the Inter Tropical Convergence Zone (ITCZ). The ITCZ keeps on moving following the position of the overhead sun. Warm air rises, which leads to conventional rainfall. The conventional rains in most cases are stormy, so this region is referred to as the thunderstorm zone. The seasonal rainfall pattern in most parts of East Africa is caused by the ITCZ.

Height

Another important factor influencing the climate of East Africa is height of land above sea level. It is also called altitude. Imagine you are flying in a balloon with a thermometer in your hand. The thermometer reading will drop as you rise higher. This is illustrated in Figure 9.6.

This means that temperature decreases with a rise in height.

This is because air is thin, dry and dust free at high altitudes.

Such air cannot absorb and keep much heat. This implies that altitude influences temperature and climate.

Latitude

The areas within the tropics, 23 and a half degrees N and S of the equator receive the most heat because the sun is overhead in these areas all year round. East Africa lies astride the equator 4 degrees N to 12 degrees S. The region experiences a Tropical Equatorial climate with constant heat and conventional rainfall. Figure 9.6 shows the influence of latitude on the climate of East Africa.

Activity 9.6
1. Copy the figure into your exercise book.
2. Explain what is taking place in the diagrams above.

Relief

Relief influences the formation and distribution of rainfall in East Africa. Rain is formed when warm, moist air blows over a mountain. The warm, moist air condenses, and forms clouds and rainfall. The side of the mountain from which the prevailing winds blow receives heavy rainfall. This is called the windward side. The side to which the winds move after dropping rainfall receives little or no rainfall. This is called the leeward side. The leeward side is said to be in the rain shadow. Figure 9.8 above shows how relief influences rainfall.

Activity 9.7
In your notebook:
1. Make notes on how the highland regions in East Africa influence rainfall formation and distribution.
2. Copy the figure above.

Distance from the Sea

In East Africa, the Indian Ocean has a great effect on rainfall and temperature. Coastal areas, for example Dar es Salaam and Mombasa, are wetter than inland areas. Clouds form when warm air from inland areas
meets cool air from the sea.

Rotation of the Earth

If the earth were not rotating, winds would move straight from one pole to the other. This is not the case, however. As the earth rotates on its axis, its speed is highest at the equator. This causes the winds blowing from the poles southwards and northwards to change their direction as they cross the equator. When this happens, we say that the winds have been deflected. Winds in the Northern Hemisphere are deflected to the right while those in the Southern Hemisphere are deflected to the left. This means that the deflected winds are forced to cause rainfall in a different area. For example, in December, the southeast shores of Lake Victoria are warmer and wetter because the winds are deflected to the area. See Figure 9.9.

The Alignment of the Coast
In East Africa, the Kenyan coast lies parallel to the Northeast Trade Winds because the coast bends inwards. The islands of Pemba and Zanzibar lie in opposition to the wind direction, so they receive relief rainfall, while the
coast of Kenya remains dry between October and December. Figure 9.10 shows the straight alignment of the East African coast.

Activity 9.8
In your notebook:
1. Copy the figure above.
2. On the map, mark the Southeast and the Northwest Trade Winds.
3. Explain why the coastal areas of East Africa receive little rainfall.
4. Read the summary below and copy it.

Activity 9.9
In groups, do the following:
1. Move around the local area.

2. Observe the type of vegetation in the area.
3. List the types of vegetation observed.
4. Write down the characteristics of the different types of vegetation.
5. Identify the climate in the local area.
6. Discuss how climate affects each type of vegetation.
7. Write a group report with diagrams of the type of vegetation observed and present it to the class.
8. Discuss the dangers of overuse of vegetation.
9. Copy the table below and fill it in.

Types of Vegetation in East Africa

How climate and vegetation types affect people’s ways of life

Activity 9.10
In pairs or individually, read the extract below and do the tasks that follow:
The climate of Kalangala district is generally moist and humid all year round. The area has small seasonal variations of temperature, humidity and wind throughout the year. The dry season is experienced between December and March, and again in June–July. The two periods have frequent thunderstorms.  The climate is characterised by high annual rainfall amounts that are well distributed. The mean annual rainfall received ranges from 1,125 to 2,250
mm.

The annual rainfall is highest over the open lake and there is a marked gradient drop of 50 mm per 1.6 km landward. The windward shores of the lake shores exposed to the moist air are wetter than the lee shores, which are sheltered from the moist winds. The rainfall maxima are associated with the onset of the southeast (SE) or northeast (NE) Monsoon winds.

The vegetation in Kalangala district is predominantly characterised by medium altitude moist evergreen forests. This vegetation occurs at altitudes ranging from 600 to 1,550 m. It forms closed stands rising 30 to 45 metres high, with abundant lianas. Grasses are generally absent or are broad-leaved and fire-sensitive.

The lakeside consists of dense and impenetrable forests with numerous shrubs on the ground. There are also small to medium sized evergreen tree species with roots extending to as high as 3.6 m up the main stem. The district is richly endowed with tropical high forest resources covering 221.5 km2.

The predominant forest cover in the district comprises tropical high-forest species. Most of the forest is filled with primates such as monkeys and other species of wildlife, including the sitatunga antelopes and exotic bird species. The Ssese islands are truly a bird watchers’ paradise.

There are a variety of fruits on the island. These include mangoes, bananas, papaya, watermelons, pineapples and jackfruit. Timber and fuel constitute the major commercial benefits of forests for the residents. As a result of these two commercial uses, the forest resources are heavily exploited.

Agriculture is the second major economic activity in the district. There are two main farming activities in Kalangala district, i.e. livestock rearing and food and cash crop production. Robusta is the main cash crop grown. The food crops comprise mainly bananas, sweet potatoes, beans and a variety of vegetables. The bananas are generally stunted and produce undersized bunches. Robusta coffee trees grow well around homesteads. The yield of the coffee trees is not as high as on the mainland.
(Adapted from: Kalangala District, State of the Environment Report, 2005)
1. In about three sentences, summarise the climate of Kalangala district.
2. Explain why the windward side of the lake shore gets more rainfall than the leeward side.
3. List the economic activities carried out in Kalangala district.
4. Describe the characteristics of the forests in Kalangala district.
5. Basing on the natural resources mentioned in the extract, suggest other likely economic activities carried out in Kalangala that are not mentioned in the extract.
6. Imagine you live in this district. What economic activities would you carry out and why?
7. If you were living in this area, what types of clothes would you wear and why?

Drawing a Climate Graph

Climate figures are always shown in a table, as you can see in Figure 9.13. This information can also be shown on a bar graph. When you look at the graph, you are able to understand the information more easily than when it is in a table. From the graph we can describe the climate of an area. You are going to draw a climate graph using the information in Figure 9.13.

Activity 9.11
Study the table in Figure 9.13 and do the activity that follows.

1. Copy the table into your exercise book.
2. Draw a graph to represent the climate of Bukoba.
3. Which is the hottest month in the year?
4. Which is the wettest month at Bukoba?
5. Calculate the total annual rainfall for Bukoba.
6. Describe the rainfall distribution at Bukoba.
7. Explain the relationship between temperature and rainfall distribution at Bukoba.

Activity 9.13
1. Using the internet or other sources, make notes on the different vegetation types of East Africa.
2. Draw a map of East Africa showing the vegetation types.
3. Explain the ways of life of people living in each vegetation zone.

What are the Factors that Affect the Climates of East Africa?
The differences in the climatic patterns you have given above are due to a number of factors. These factors are mainly physical in nature. In some regions human activities are increasingly playing a role. These factors include relief/altitude, water bodies, the Inter Tropical Convergence Zone (ITCZ), latitudes, the location of the earth, coastal alignment, vegetation cover, the distance from the sea, wind masses and human activities.

Activity 9.14
In pairs or groups:
1. Conduct library research and make notes about factors influencing the climate of East Africa.
2. Present your report to the class through discussion.

Chapter Summary

In this chapter, you have learnt:
1. that East Africa has several climates because the region has different relief features, water bodies, and winds blowing across the region.
2. the different types of vegetation in East Africa and their characteristics.
3. how the different climates and vegetation types of East Africa are distributed and related.
4. that people’s way of life is largely influenced by climate and partly by vegetation.
5. how the apparent movement of the sun and the movement of the ITCZ affect temperature, wind movement and distribution of rainfall in East Africa.