Wet and Dry climate of Africa

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  • Created on: 09-01-15 13:44
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  • The Tropical Wet and Dry Climate of Africa
    • Location of countries with a tropical wet and dry climate
      • These countries are found south of the tropic of Cancer and north of the tropic of Capricorn
      • They are found close to the equator
      • Many central African countries
      • Other countries include, Northern Australia, Brazil, Honduras, Thailand and Vietnam
    • CASE STUDY 1 : KANO, NIGERIA
      • Completely dry for 4 months of the year N-F
      • 812 mm of rainfall  within 8 months of the year, most from J-S
        • Similar rainfall per year as Huddersfield, however in a shorter time period
      • Location of Kano, is halfway between the tropic of Cancer and the Equator
    • Understanding the Wet and Dry Climate
      • The earth climate pattern is controlled by incoming solar radiation ( the Sun)
      • At the equator, solar radiation in the form of ultraviolet radiation is coming from a perpendicular 90 degree angle, meaning it is concentrated into a small area, so the energy is densely packed, this passes through the atmosphere and heats up the ground
      • 30 degrees N/S of the equator, the ultraviolet radiation is coming from a oblique angle and therefore covering a larger surface area, meaning the energy is spread out and less concentrated
      • Once the shortwave has heated the ground, some of the radiation is reflected back into the atmosphere as shortwave, infrared radiation warming the air above
        • This air, expands and becomes less dense than the surrounding air, and so rises,
          • This air starts to adiabatically cool, because particles are expanding, condensation takes place which creates rain above the equator.
            • The air is unable to rise any further and so diverges either N or S, then starts to drop to the right if at the north, and left if at the south due to the coriolis effect which is a drag caused by the earths spin
              • as the air drops it starts to adiabatically warm, where the particles become closer together and therefore heat up, leading the evaporation of moisture and high pressure. Meaning it is dry at this area
                • The dry air creates the trade winds which return to the inter-tropical convergent zone, which with solar radiation create the earths climate pattern
          • Low pressure
      • The dry air creates the trade winds which return to the inter-tropical convergent zone, which with solar radiation create the earths climate pattern
    • The seasonal change
      • Because the position of the overhead sun changes throughout the year due to the earths tilt. This causes seasonal movements of the 'Thermal equator', the ITCZ and the pressure belts of the Hadley cell.
      • This has a significant impact on the climate of tropical regions of Africa
      • On the 21st of March the sun is directly overhead at the Equator, this is when the wet season starts in Kano.
        • This is because of the low pressure formed with the rising air and subsequent cooling, leads condensation to take place and convectional rain to fall.
          • At this time, kano is in the low pressure band
      • On the 21st of June, the sun is overhead at the tropic of Cancer, 23 degrees north.
        • This means that Kano is further into the low pressure zone, meaning a rapid increase in rainfall, although it is closer to the overhead sun, there is also increasing cloud cover and therefore temperatures drop.
      • on 21st of September the overhead sun returns to the equator, meaning Kano is still in the low pressure zone but further from the overhead sun, meaning a decrease in rainfall and increase in temperature
      • On the 21st September the overhead sun goes southwards 23 degrees so that it is overhead at the tropic of capricorn
        • This means Kano becomes part of the high pressure zone, the temperature is lower due to a larger distance from the sun.
          • The falling air in these areas leads to adiabatically warming, meaning moisture is evaporated and clear skies are formed
          • Kano is affected by the NE trade winds which blow over the Sahara Desert, meaning it is warm and dry.
    • CASE STUDY 2: DODOMA, TANZANIA
      • Also has a tropical wet and dry climate
      • Located south of the Equator
        • This means it experiences its wet climate from December to march
        • And has four months of dry weather from June to September
      • Changes over time
    • Changes of Space
      • Climate changes progressively as you move from high pressure centres over the tropics, through the tropical wet/dry climate to the equatorial climate
      • This causes a change in vegetation from desert to semi-arid scrub to savannah to tropical rainforest
        • Climate changes progressively as you move from high pressure centres over the tropics, through the tropical wet/dry climate to the equatorial climate
        • Called an ECOCLINE
      • Areas that are further from the equator, have a wider seasonal variation than those that are closer to the equator.
        • This is because throughout the year, the movement of the overhead sun means that they move in and out the low and high pressure zones
          • So, they experience both variations, wet and dry.
          • Areas that are close to the equator, stay in the ITCZ all year long and therefore have little variation due to always being in the low pressure zone
            • Should always be wet however due to the different altitudes this isn't always the case

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