ITCZ Aim- Describe and account for rainfall patterns across West Africa

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ITCZ Aim- Describe and account for rainfall patterns across West Africa Lagos receives a high amount rainfall all year round with 1625mm. There are two distinct peaks in summer and autumn. Rainfall in January is low at about 50mm, this is because the ITCZ is lying to the south of Lagos and the mT air mass is offshore. As the ITCZ starts its migration northwards the rainfall begins to increase to a maximum of 350mm. This is because the rainfall belt is km behind the ITCZ and the mT air mass dominates. There is however a decrease at the height of summer probably because the ITCZ is too far north and the rain belt no longer extends as far south as Lagos. As the ITCZ migrates more rapidly south in autumn Lagos receives a second peak in rainfall, decreasing towards the end of the year when the ITCZ is further south.

ITCZ Aim- Describe and account for rainfall patterns across West Africa Kano located in central west Africa and has one distinct rainy season. In January there is no rainfall and this is because the ITCZ is lying to the south of Kano. Thus the cT air mass is dominating over much of north west Africa bringing very dry conditions (harmattan wind), and warm temperatures. As the ITCZ starts to move northwards in spring a small amount f rainfall is received in Kano, it isn’t until the summer that a maximum of 300mm of rainfall is received because the ITCZ is now north of Kano and the rain belt is km behind. The temperature is decreased in the summer because the mT air mass dominates over much of the continent it brings slightly cooler temperatures on shore from the sea. As the ITCZ migrates south again in the autumn the rainfall decreases and the cT air mass dominates once more bring dry warm weather again.

ITCZ Aim- Describe and account for rainfall patterns across West Africa 1995 Ouagagougou January very warm and dry because the cT air mass is blowing out of the Sahara, with a hot dusty wind (harmattan). Spring, the temperature will increase with the movement of the overhead sun. Summer- temperature decreases and rainfall reaches it seasonal maximum. Due to the mT air mass bring cooler temperatures. The ITCZ is to the north bringing the rain belt km behind it. Autumn- Temperatures begin to rise again, before falling back to winter low and rainfall decreases. Because the ITCZ moves southwards and the cT air mass returns with warm dry weather.

ITCZ Aim- Describe and account for rainfall patterns across West Africa There is a varied rainfall distribution over west Africa. Lagos in the south receives the highest amount of rainfall, 1800 mm. Whereas Agades in the far north, receives the least amount of rainfall at 160mm. As you move northwards rainfall levels decline, Minna 1350mm and Zinder 550mm. Rainfall is associated with the movement of the ITCZ, this is where the trade winds converge at the thermal equator. The thermal equator moves in accordance to the seasons, i.e. the position of the overhead sun. The sun is directly over head at the equator twice a year, meaning that the ITCZ is over Lagos twice in the year. Whereas in the north the ITCZ is only overhead once. When the ITCZ lies to the south, the cT air mass dominates over much of north Africa bring very dry conditions. The Harmatten wind blows southwards from the Sahara, it is very dry and dusty. Its only when the ITCZ starts migrating northwards that the mT air mass dominates bringing with it moist unstable air, and producing rain where it meets the cT at the ITCZ.

ITCZ Aim- Describe and account for rainfall patterns across West Africa Points could include for Jos: Marked seasonal variation in precipitation- High annual total but most rain falls between April and September. Dry Between November and February, due to dominant hot, dry cT air mass blowing outwards from the Sahara. Reference may also be made to the hot, dry, dusty Harmattan wind. Increase in temperature (monthly peak of 23 C in March) before onset of rainy season. Temperatures decrease in summer months ( Mean low of 17 C in July) as rainfall increases to a maximum. The steady rise in rainfall amounts from March’s modest 20mm, to far more significant totals in April and May and the high amount in June-September can be attributed to the northward movement of the I.T.C.Z. and the increasing influence of the moist mT air from the Gulf of Guinea. Mark out of 10, award up to 6 marks for either Description or Explanation.