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CfE H Geography: Human Environments - Rural Revision
Transcript of CfE H Geography: Human Environments - Rural Revision
You need to use your class notes to effectively revise each topic.
This is the deterioration of an area over time, through physical or human processes.
This is the spread of desert conditions in arid regions due to human activities, drought or climate change
AREAS OF THE WORLD AT RISK OF RURAL LAND DEGRADATION
WHY SHOULD WE CARE?
Soil erosion and land degradation occur when rainfall is variable. Extended periods of low
can result in drought and vegetation dies (thus protection from rain is lost). When followed by periods of heavy, intense rainfall and flash floods soil is washed away as large drops break up the soil and increased surface run-off transports the soil. The most erosive rain occurs in tropical and sub-tropical areas.
erosion is most common in arid or semi-arid areas. It is encouraged by loose, dry and fine soils, flat land surfaces, little or no vegetation, large fields and strong winds.
- Erosion is most likely on steep, short, convex slopes and less likely on long, gentle concave slopes. Soils most at risk are those that have no vegetation, open, flat landscapes.
- This occurs when rain breaks up the soil into individual particles by direct impact, lifting and dropping the particles into a new position. The bigger the rain drop, the faster it falls and harder it hits the soil. Those that fall in thunderstorms (30km/hr) can have an explosive impact. The force can loosen soil, break granules into finer particles and move particles considerable distances from the impact (e.g. 2m). On flat areas the particles fall randomly, on sloped surfaces they will be moved downslope.
- The particles displaced by rainsplash can find their way into pore spaces and clog up the soil to form a thin crust on the surface. This leads to less infiltration and more surface run-off which transports displaced particles. The crust begins to disintegrate by the first few rain drops of a rain storm but is reformed again as fresh particles from rainsplash move into pore spaces. During heavy rain on slopes less than 5 degrees sheet erosion will occur. A thin film of water will flow smoothly downslope (sheet flow) and transport any loose particles. Due to cultivation this process is not often noticed until the topsoil is greatly thinned.
RILL & GULLY
- These are the most serious forms of soil erosion by water and occur on steep slopes with significant run-off. During heavy rainfall water that is unable to soak into the ground will find its way into natural channels. It will gain volume, speed and power and transport particles downslope. Small, eroded channels criss-crossing the land will form (few cm deep). These are rills, they are not permanent and may be destroyed by the next rainstorm or ploughing.
Gullies may develop if water is concentrated into one channel and cuts deep into the soil and can cut into the entire soil profile. These are permanent features several metres deep and wide. They can develop from rills or form where there is a break in vegetation cover where run-off develops a depression that traps water and is further eroded.
- The denser the vegetation the more protection the soil has from erosion. Dense root systems bind the soil together, dense ground cover intercepts raindrops protecting the soil from their full force. Dense vegetation will also protect the soil from the effects of wind.
- The rate at which water drains through soil will depend on its infiltration rate. Coarse, sandy soil has large particles and pore spaces resulting in high infiltration and little surface run-off therefore less erosion. Finer soils with smaller pore spaces have a lower infiltration rate and therefore more surface run-off and more erosion.
- Larger particles are less easily moved by water or wind, therefore coarse sand soil is less likely to be blown away than finer clays and silts (providing it is dry)
Improved medical care and high birth rates in some areas, such as the Sahel results in rapid
growth. The increase in population results in greater pressure on resources to produce food. E.g. Burkina Faso, Chad, Mali = growth of population 2.5% per year where as food production is increasing at just 1% per year. This leads to overcultivation, overgrazing, deforestation, urbanisation and cash crops, which all contribute to land degradation.
- There has been a rapid growth of urban populations in the Sahel as families move away from rural areas for jobs, better standards of living and education. Growth and development of smaller settlements have also increased and these all require firewood, which leads to deforestation, which in turn accelerates land degradation.
- Due to increased population arable farming yields need to be increased. As a result fallow periods (for soil to regenerate) are shortened and soil looses nutrients. Increase in the amount of land used for farming has forced the use of fragile, marginal areas that cannot sustain farming practices and leads to desertification.
Has increased due to increasing populations.
removes the binding effect of roots and the protection offered by vegetation from rain and wind. Shortage of fuelwood has led to families using animal dung for domestic energy, which would normally be used for fertiliser therefore the soil is further degraded as it is deprived of nutrients. In the Sahel an average family requires about 1kg of wood each day for cooking alone.
- Population increase has led to the increase in size and number of herds, which coincides with the location and increase in the use of wells to provide water. This has put pressure on grazing areas particularly around the wells and has resulted in the loss of vegetation leaving the soil exposed. It has also led to trampling and compaction of soil which results in increased run-off and erosion.
During 20th century some farmers in the Sahel grew
e.g. cotton and rice. This led to monocultures (growing only one crop which depletes soil of same nutrients continuously = infertile) and often inappropriate farming methods such as flood irrigation.
up and down the slope creates ready made channels that transport water downslope this leads to rills and gullies being quickly formed. Ploughing parallel to prevailing wind direction can accelerate erosion. Fine ploughing, which breaks up particles at the surface leads to fine, detached particles that can be easily transported by wind.
- e.g. Flood irrigation in Niger can lead to the salinisation of the soil. This can occur when there is not proper drainage and the water table rises. Water will evaporate from the top layers of the soil, leaving behind salt = increased salinisation of the soil which can eventually poison crops and the land is degraded.
WELLS & WATER HOLES
- These areas attract population and as a result farming practices and overgrazing which accelerates land degradation. In addition to this wells and water holes can lower the water table, which can cause changes to the natural vegetation. These changes can lead to land degradation as the vegetation may no longer be sufficient to protect the soil from water and wind.
- Repeated planting of the same crop results in nutrient depletion and breakdown of soil structure making it easier for wind and rain to carry away soil particles. This is particularly common practice in the growing of cash crops.
- Leaving soil exposed and vegetation free leaves it open to wind and rain erosion with sheet erosion becoming common.
results in the reduction of pore spaces and therefore infiltration rates. This increases surface run-off which transports soil particles.
- Use of available manure is not always adequate to restore the soil, as a result soil became exhausted and easily eroded by wind and rain.
INTRODUCTION TO THE SAHEL
CAUSES & CONSEQUENCES OF LAND DEGRADATION
SOLUTIONS TO LAND DEGRADATION
LIVESTOCK PROJECT, BURKINA FASO
INTEGRATED DEVELOPMENT PROJECT, NIGER
Farmers were educated in irrigation techniques allowing them to take ownership of their own schemes.
Moving to the future, more schemes and land ownership will be passed to farmers to take greater responsibility for their own schemes.
Farmers are adapting to erratic rainfall conditions.
Planting new trees binds the soil together and provides shade to prevent moisture loss, a windbreak for crops and encourages nutrients to be returned to the soil.
They may also provide an alternative source of food e.g. fruit and nuts.
STRATEGIES USED IN THE SAHEL
Farmers have been educated to improve there terraces and implement 'Crescent-shaped terraces' which can withstand monsoon rainfalls.
Stone lines built along contour lines allow rainwater to be used better and in turn helps to reduce erosion levels.
They increase infiltration and trap sediment improving the fertility of the land.