Changing Rainfall and Water Availability in East Africa: Supplementary Material to Lesson 3 of the “East Africa Climate Change Curriculum Unit” Available at Lesson 3 by Dwight Sieggreen & Barbara Naess. PowerPoint based on materials by Jennifer M. Olson. The Eaclipse Project is supported by National Science Foundation Award No. BCS/CNH © 2010 Michigan State University Board of Trustees

Lesson 3: Changing Rainfall and Water Availability in East Africa Supplementary Material 2

In this lesson you will Learn the main factors that affect rainfall patterns in Africa Compare the water cycle in two different ecosystems Use the water cycle to understand where water is lost from each ecosystem 3

Major influences on Africa’s climate zones 1.Intertropical Convergence Zone (ITCZ): As the ITCZ moves north and south, it determines the rainy seasons 2.Elevation: The mountains and highlands are cooler and wetter, and the windward side of a mountain gets a lot of rain (orographic effect) 3.Nearness to the coast: there is more rain on the coast 4

The ITCZ is a belt of rainfall that governs the rainy seasons around the equator (between Tropics of Cancer and Capricorn) It is an area of low pressure: the sun heats the earth’s surface, the surface air warms and expands, and it rises up like a fountain As the hot air rises, it precipitates out water  rainfall The Intertropical Convergence Zone (ITCZ) 5

ITCZ Rainbelt in July The ITCZ moves, within the tropics, with the peak of the sun In July it is at its farthest northern point MSU LUCID: Bilal Butt © MSU Board of Trustees 2010 Adapted from Stock1995. Africa South of the Sahara, p31. 6 Rainfall

ITCZ Rainbelt in January In January, the ITCZ is at its most southern point Maritime southwesterly (wet) winds cause heavy rain Northern Africa is dry Adapted from Stock1995. Africa South of the Sahara, p31. MSU LUCID: Bilal Butt © MSU Board of Trustees Rainfall

MSU LUCID: Bilal Butt © MSU Board of Trustees

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Orographic Rainfall Elevation affects rainfall. As winds hit a mountainside on the windward side, air is forced upwards and cools. The cool air cannot hold moisture and rain precipitates out. The wind, now dry, flows over the mountain peak and descends on the leeward side. It doesn’t rain and leaves that side of the mountain dry. 20

Source: 21

22 Moist Air Rising and Forming Clouds Along a Mountain Side

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Mt. Kenya Windward side Leeward side - dry 24

Proximity to the Coast Coastal East Africa receives torrential rains from moist air masses moving inland from the Indian Ocean This means that coastal areas have significantly more rainfall than inland areas 25

Map source: U.S. Central Intelligence Agency,

Source: Tanzania Meteorological Agency 27

Source: Tanzania Meteorological Agency 28

Summary of factors affecting rainfall Tropical areas receive highly seasonal rainfall due to ITCZ –Some equatorial regions receive almost constant rainfall –North & south of equator, there are mirrored belts of decreasing rainfall Rainfall varies according to elevation – orographic effect Rainfall is higher on the coast 29

How will rainfall affect vegetation? Vegetation growth is closely associated with rainfall Reliability: In general, the less rain a region receives in an average year, the less reliable the rainfall Drought: savanna livelihood systems must be capable of withstanding extreme variability of rainfall, including droughts 30

Review Questions What is the Intertropical Convergence Zone (ITCZ) and how does it affect rainfall in East Africa? What is orographic rainfall and how does it affect rainfall on mountainsides? How does the ocean affect rainfall in locations on the coast? What differences did you see in the change in average rainfall in Arusha (highland savanna) and Zanzibar (coast)? 31

Source: U.S. Geological Survey 32