Developing Country – Semi Arid Area. Case Study – Sahel Learning Intensions: 1. Location and climate of the Sahel. Causes of land degradation in Sahel – Human and Physical. http://www.canada.com/cms/binary/5314242.jpg

Location of the Sahel Sahara Desert Sahel

Physical Causes of land degradation - Sahel Inter Tropical Convergence Zone (ITCZ) This is covered in the Atmosphere section of the course and explains how the 2 air masses (from the north and south of the Sahel) bring about the short wet and long dry season. Describe the climate of the Sahel. To help with the description write about: What is the highest temperature and when Lowest temperature and when. Range of temperatures (difference between highest and lowest). When is the highest and lowest rainfall and when. What is the total rainfall.

Physical Cause – main points: Sahel has a long dry season – when the area is affected by the tropical continental air mass form the Sahara. Area has become drier since the 1970s Drought is more common Rainfall variability is increasing, especially further from the sea – the Tropical Maritime air mass is not penetrating far enough inland.

The Human causes of land degradation relate to the land being overused The Human causes of land degradation relate to the land being overused. This is due to one main reason… POPULATION INCREASE An increase in population means that more demands are put on the land for resources – food and fuel. The land is then put under stress causing the plants to fail, the soil to lose its structure and therefore blown or washed away. Complete page 12 in your booklet. There are 4 human reasons for desertification to occur. Overgrazing Overcultivation Vegetation clearance – forests Salinization and waterlogging.

OVERGRAZING What does the term ‘carrying capacity’ of the land mean? Maximum number of animals (or crops) that the ground can support before degradation occurs Overgrazing means that there are too many animals being kept in an area, removing all the vegetation and trampling the ground. This is made worse if many animals are kept in one area. In times of drought people move their animals around waterholes/ wells where the animals overgraze the soil.

How cattle trample an area around a waterhole. Removing the vegetation means that the soil is left exposed to the wind and the heavy rain. Animals also trample and compact the soil reducing infiltration rates and increasing surface run-off. This causes 2 problems, firstly, increasing soil erosion by water. Secondly, reducing the amount of water in the soil (eg lower water table) and therefore less water for future use. As vegetation removed herders must move further afield, thus the overgrazed area gets bigger. Waterhole Land directly around the waterhole overused

Leaves help provide shade from sun reducing evaporation from soil DEFORESTATION Cutting down the trees for fuel. Draw a simple diagram of a tree and label it to explain how trees help to reduce soil erosion. Leaves help provide shade from sun reducing evaporation from soil When all trees removed people use dried animal dung as fuel. This also causes a problem as it is no longer being added to the soil. Leaves help protect the soil below from rain splash Trees/ vegetation lifts the wind and reduces soil erosion Leaves add some nutrients to the ground when they decompose Roots help bind soil together

POOR IRRIGATION TECHNIQUES – SALINIZATION/ WATERLOGGING. When farmers irrigate their crops salinization can occur. This is due to the high evaporation rates which brings salt to the surface as water is drawn up through the layers of soil. Also if farmers flood the fields, due to poor techniques, then crops can not grow and the land will be left bare.

Desertification - reminder In this region of the world the process of land degradation is often called DESERTIFICATION – this is the process of the land turning into desert.