This is a focussed revision guide for use closer to the final exam – a star* next to the slide number indicates a slide you must become an expert about as the exam approaches Ideas how to use the revision cards: - Colour code the cards to show how confident you are with the topic - Ask someone at home to test you - Test yourself & highlight key words - Annotate (label) the cards - Re-write your own definitions - ‘Look, cover, check’ - Draw a mind map for some topics - Expand on key words - Explain a topic to someone else - Cut out cards & stick around a room 1
Extreme Environments 2* Extreme Environments What do we mean by ‘extreme environments’? Extreme environments have specific characteristics: • An extreme environment is a region, place or area that is at the very edge of what people, animals and plants can survive in. • This is because of a combination of characteristics that make life a challenge: • hazardous conditions • unstable environment • remote/isolated • harsh climate • harsh landscape • e.g. A hot desert is classed as an extreme environment because of high daytime temperatures, low night time temperatures, lack of rainfall, isolation and a lack of resources including food. • A mountain environment is extreme because of low temperatures, large amounts of snow/ice, high winds, thin air/less oxygen, steep slopes, thin soils/bare rock, avalanches, earthquakes/volcanoes, isolated from populated areas with poor communication links. • Prepare to explain how these factors make life a challenge – e.g. thin air makes life in the mountains a challenge because it is hard to breathe and even the simplest of tasks become more physically demanding.
Extreme Environments 3* Hot Desert Environments Where are hot deserts found? Hot deserts are found in particular areas of the world: • The location of hot deserts can best be described using the following phrases: • between 10° and 30° north and south of the Equator (on or close to the Tropics of Cancer and Capricorn) • to the west of large land masses – continents • close to coastal areas • associated with trade winds • on the leeward side of mountains
Extreme Environments 4 Hot Desert Environments Where are hot deserts found? Hot deserts are found in particular areas of the world: • Hot deserts are found in particular areas of the world. There are major hot desert areas on most continents. • The Thar Desert is located to the south west of Asia. It is to the west of the Himalaya Mountains and on the coast of the Indian Ocean, between the lines of latitude 10° and 30° north of the Equator (° = degrees). • The Australian Desert is located to the west of Australia (continent - Oceania). It is west of the Great Dividing Range and between 10° and 30° south of the Equator. • The Atacama Desert is located to the west of South America, to the west of the Andes Mountains and on the coast of the Pacific Ocean between 10° and 30° south of the Equator. • The Arabian Desert is located in the Middle East (Asia) between the latitudes of 10° and 30° north of the Equator. • The Kalahari Desert is located in the south of Africabetween 10° and 30° south of the Equator. • The Mojave Desert (Sonora Desert on the map) is located to the west of North America and the Rocky Mountains at 30° north of the Equator.
Extreme Environments 5* Hot Desert Environments What are hot desert climates like? Describe the climate of Timbuktu, Mali using evidence from the graph. Model answer: Timbuktu has a hot desert climate. Temperatures are high in the summer reaching 34°C in June. Temperatures then decrease into the cooler winter reaching a low of 22°C in December. Temperatures then rise again between January and June. Rainfall is low and intermittent throughout the year. There are five months with no rainfall, from November to February and again in April. Rainfall then rises to a high of 80mm in August before decreasing again until November when there is no rainfall. • You could also mention: • the annual range of temperature = difference between the highest and lowest in the year – in this case = 12°C. • the average annual precipitation = the total rainfall during the year – do a quick calculation – in this case = 225mm. • the link between temperature and rainfall – in July/August there is more rain – there are more clouds in the sky so temperatures drop as sunlight is blocked.
6* Extreme Environments Hot Desert Environments What are hot desert climates like? There is a large diurnal(difference between the day and night) range in temperatures in the desert. Why are deserts cold at night? At night a lot of heat escapes. This is because there are v. few clouds, which means that the heat can escape. Why are deserts hot during the day? During the day, the sun heats up the ground. This is because there are v. few clouds to stop the suns rays.
Extreme Environments 7* Hot Desert Environments Where are hot deserts found? Location of hot deserts is influenced by a variety of physical factors: Reason 1 Angle of the Sun’s rays Deserts are hot because they are found between 10° and 30° north and south of the Equator. The earth is curved. This means that the energy from Ray B is spread/ dispersed over a greater area – the energy is less intense. This is shown by ‘X’ on the picture. Whereas the energy from Ray A is concentrated on a smaller area. This is shown by ‘Y’ on the Diagram. The sun shines from a high angle in the sky so temperatures are high. X Parallel rays of sunshine Y
Extreme Environments 8* Hot Desert Environments Where are hot deserts found? Location of hot deserts is influenced by a variety of physical factors: Rainfall in hot deserts is low and intermittent/irregular – the rainfall is unreliable – one heavy shower could be followed by months, or even years, without rain. Low rainfall is linked with high pressure (falling air): To understand why deserts receive little rain, we first need to know why rain occurs: Rain only forms when moist air rises, cools and moisture condenses to form clouds. In deserts, the air does not contain much moisture & the air is usually falling (high pressure) meaning it warms and evaporation of moisture occurs – no clouds form and it is dry. Deserts are dry/arid – there are high evaporation rates – any moisture in the desert doesn’t last for long because it is so hot.
Extreme Environments 9* Hot Desert Environments Where are hot deserts found? Location of hot deserts is influenced by a variety of physical factors: Deserts can be found where air falls - reasons why air falls: High pressure -Due to the Sun’s heat, air rises at the equator & falls near to the tropics (Cancer/Capricorn) where deserts are located = dry. Rain shadow - Air blows across a mountain. The air then loses all of its moisture on the other side as it falls, warms and evaporation occurs = dry. Coastal deserts- If the ocean is particularly cold due to cold ocean currents, then the air around the coast is cooled, meaning that it will not rise & condense = dry.
Extreme Environments 10* Hot Desert Environments Where are hot deserts found? Location of hot deserts is influenced by a variety of physical factors: Trade-winds: the prevailing (most common) wind direction plays a very important role in desert climates e.g. the prevailing wind for the Sahara Desert in Africa is from the north east. This wind blows over land, so contains quite ‘dry air’ as it does not pick up moisture from the sea. The same is true for other deserts. Winds blow over large areas of land before reaching the desert so they become dry (trade-winds) – these winds are also warm because they form from falling air = increase desert temperatures as well.
Extreme Environments 11 Hot Desert Environments Where are hot deserts found? Location of hot deserts is influenced by a variety of physical factors: Why is the climate in a desert hot and dry? Deserts are located where they are because of a variety of physical factors which make the locations hot and dry - remember to develop your answers with explanation: e.g. LOOK AT THESE STATEMENTS TAKEN FROM A GCSE MARK SCHEME - long way from oceans so all precipitation (rain) falls before air mass reaches desert; wind blows overland so no source of moisture; no clouds so sun’s heat is not prevented from reaching earth; overhead sun so rays are powerful; high pressure so descending dry air; rain shadow so rain has fallen on mountains etc.
Extreme Environments 12 Hot Desert Environments What are hot desert climates like? So we know that the deserts are hot and very dry. There are however landforms in hot deserts created by running water – why is that? Flash flooding can occur in deserts. During the day the ground gets very hot and heats the air above it. The heated air rises and cools – condensation occurs forming clouds, resulting in rain – often in the form of a thunderstorm. Flash flooding occurs because the ground has been baked hard by the sun and the large storm raindrops cannot sink into the surface of the ground. The rains run across the surface causing flooding – fast flowing rivers can form – they erode the landscape.
Extreme Environments 13* Hot Desert Environments What characterises the ecosystem of a hot desert? Ecosystems in hot deserts are finely balanced: The hot desert is an extreme environment – itis at the very edge of what people, animals and plants can survive in – as a result the ecosystem is finely balanced – even the smallest changes to the ecosystem will have an impact on plants and animals – e.g.if human activity damaged the vegetation (e.g. poor farming methods or global warming resulting in the desert becoming drier), there would be less for insects, lizards and rodents to eat – this would mean less for larger lizards, scorpions, snakes and spiders to eat – as a result the numbers of hawks and foxes could decrease as they would have less to eat.
Extreme Environments 14 Hot Desert Environments What characterises the ecosystem of a hot desert? Ecosystems in hot deserts are finely balanced: 1.Food chain = a chain of names and arrows, showing what species feed on 2. Food web = a network of food chains, showing how they link together 3. Producer = plants are producers - using sunlight, carbon dioxide, water and nutrients from soil, they can produce everything they need to stay alive 4. Consumer = something that eats other living things in an ecosystem 5. Predator = an animal that naturally preys on others 6. Carnivore = an animal that eats meat – other animals 7. Herbivore = an animal that eats plants 8. Decomposer = fungi and bacteria are these – they break down dead and waste material in an ecosystem 9. Ecosystem: a unit made up of living things and their non living environment – for example – a desert
Extreme Environments 15 Hot Desert Environments What characterises the ecosystem of a hot desert? Ecosystems in hot deserts are finely balanced: Food chains – hot deserts • A food chain shows what eats what. They always start with plants. The arrow means eaten by: Cacti Rodents Snake Hawk
Extreme Environments 16 Hot Desert Environments What characterises the ecosystem of a hot desert? Ecosystems in hot deserts are finely balanced: Food webs – hot deserts • This is a bigger version of a food chain as often several consumers eat the same food. Consumers can be both small and large predators. The larger the predator the higher up the food web it will be.
Extreme Environments 17* Hot Desert Environments What characterises the ecosystem of a hot desert? Ecosystems in hot deserts are finely balanced: • The complete food web for a desert can be large and complex – examples of producers and consumers include: • primary producers – cacti and creosote bushes • primary consumers – insects, lizards and rodents • consumers – carnivores/predators – snakes, lizards and scorpions • larger predators – hawk and fennec fox Remember – the arrow head points to the consumer that eats the plant and animal at the other end of the arrow A hot desert food web
18* Extreme Environments Hot Desert Environments What characterises the ecosystem of a hot desert? For any vegetation to survive in a hot desert it must adapt. The main challenge is the heat & lack of water. • 1) Xerophytes These plants have made physical adaptions to survive the desert – their physical features allow them to survive – e.g. cacti. Some of the features of cacti are: • - spines/spikes – these deter predators and help to break up wind – reducing the amount of transpiration (plants giving off water moisture) by creating still air around the plant • shallow roots – these quickly draw up any surface rainwater • deep roots – reach towards deep underground water stores • ‘pleated’ body – the cactus can swell up to take in water • green body – takes on role of photosynthesis because there are no leaves • small surface area (no leaves) – to reduce transpiration • large fleshy stems/thick waxy skin – stores water/makes sure no water is lost • white upper surface – reflects the sun’s rays
19 Extreme Environments Hot Desert Environments What characterises the ecosystem of a hot desert? For any vegetation to survive in a desert it must adapt. The main challenge is the heat & lack of water. Ephemerals change their behaviour in order to survive: 2a) Ephemerals (plants – shrubs and bushes) These plants lie dormant for months, or even years in the desert until it rains e.g. creosote bush. These plants grow & flower very quickly (within a few days) before the water gets evaporated or soaked away. 2b) Ephemerals (seeds) In deserts there are many seeds waiting to be germinated. When the rains come they will quickly start to grow into plants, taking advantage of the conditions – the desert sand verbena seeds can resist drought for up to 2 years.
20 Extreme Environments Hot Desert Environments What characterises the ecosystem of a hot desert? Animals need to adapt in order to survive in desert environments. They have to cope with extreme temperatures, lack of food and lack of water. To avoid daytime heat, many desert animals are nocturnal; they burrow beneath the surface or hide in the shade during the day, emerging at night to eat. Many desert animals do not have to drink at all – they get all of their water from the moisture in food.
21* Extreme Environments Hot Desert Environments What characterises the ecosystem of a hot desert? How have camels adapted to life in deserts? Thick fur & underwool – warmth at night & insulation against sun in day Fat/water stored in humps - energy reserve Two rows of eyelashes– protects against sand & sun Concentrated urine to retain as much water as possible Nostrils can be closed to keep out sand Broad, flat leathery pads on hooves to spread out weight on sand Long, strong legs – travel long distances, carry heavy loads & body further away from sand Can drink up to 50 litres of water in a few minutes Thick leathery patches on knees to protect when resting on hot sand
Extreme Environments 22 Hot Desert Environments What are hot desert landscapes like? Physical processes of weathering, erosion, transportation and deposition form distinctive hot desert landforms: Why does the climate in the hot desert lead to a desert environment as shown in the photograph? High temperatures and low rainfall means very little vegetation can grow – soil is not bonded and can erode away – so sand encroaches (takes over). To understand where the sand comes from you need to be familiar with: Weathering – the breaking up of rocks in the place they are found. Erosion – the removal of material (eventually in the form of sand) loosened by weathering.
23* Extreme Environments Hot Desert Environments What are hot desert landscapes like? Weathering is the breaking up of rocks in the place that they are found. For example: a) Physical weathering. This includes freeze-thaw weathering (at night ice expands in a crack, thaws in the day, then re-freezes expanding again) and exfoliation (minerals in rock heating and cooling at different rates – the resulting strain on the rock causes layers to break off like the layers of an onion). freeze-thaw weathering exfoliation/onion skin weathering
24* Extreme Environments Hot Desert Environments What are hot desert landscapes like? b) Chemical weathering. This includes salt crystallisation (water evaporates in a rock crevice & leaves behind salt, which expands and forces the rock apart) and hydration (water reacts with chemicals in the rock causing them to break down). c) Biological weathering. This is when plant roots grow into a crack in the rock and force the cracks open. Burrowing animals such as the fennec fox have a similar effect. Erosion is the wearing away and removal of material. In deserts erosion is mainly caused by the wind. Although flash floodingcan also happen with running water removing loose material. Both occur as there is little vegetation to hold/bind sand and any soil – this can result in deflation = gradual removal of sand and dust to leave a flat surface or hollow in the rock. The main form of erosion is abrasion– the sandblasting effect of sand particles carried by the wind – it can erode the rock into unusual shapes.
25* Extreme Environments Hot Desert Environments What are hot desert landscapes like? • Erosion involves material being transported away – the method of transport depends mainly on the size of the particle being moved by the wind: • traction = large particles cannot be picked up by the wind – they roll along the surface of the desert. • saltation = medium particles bounce or jump along the desert surface. • suspension = small particles are light enough to be almost constantly carried by the wind. Deposition is the laying down of material that has already been eroded. Material from wind erosion is often deposited – laid down to form dunes & flash floods carry material and deposit it further along a valley & across flood plains.
26* Extreme Environments Hot Desert Environments What are hot desert landscapes like? Rock pedestal– these are sometimes called mushroom rocks as they are often ‘top heavy’. Over time, the wind (which carries particles of sand) wears away the rock. This type of erosion is called abrasion. A rock pedestal erodes more in places than others. This is because softer (less resistant) rock erodes more quickly than harder (more resistant) rock and because much of the erosion takes place within the first metre of the ground. Example of a rock pedestal Classic mushroom shape at the top More resistant rock worn away slowly Less resistant rock worn away quickly Most erosion within first metre of ground as wind lifts material
27 Extreme Environments Hot Desert Environments What are hot desert landscapes like? Yardang: formation Yardangs often form in alternate vertical bands of hard and soft rocks. The weaker rocks are less resistant and erode more quickly. The harder rocks are more resistant and are left as ridges. Stage 1 – flat surface Stage 2–Differential erosion due to abrasion Key Hard, resistant rock Softer, less resistant rock
28 Extreme Environments Hot Desert Environments What are hot desert landscapes like? Yardang: formation Yardangs are long and thin in appearance. The ridges become more pronounced due to erosion. They also often occur parallel to the prevailing (most common) wind direction, this determines where most erosion will occur. Stage 3 – Ridges become more pronounced Diagram is plan view
29 Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: when rain does fall in the desert the resulting running water (flash flooding) can erode the landscape by water abrasion (sand and stones carried by the water scrape the desert landscape) and hydraulic action (water forced into cracks in rock causing the rock to eventually break up). Landforms created by water erosion: CANYON (a deep, steep-sided valley) - this starts as a plateau (a high, flat area of land). Rainwater erodes cracks & less resistant rock in the plateau. These get wider over time and eventually form a canyon.
30 Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: MESA (a flat-topped mountain with steep sides) - a plateau has a layer of hard rock (cap rock) above soft rock. Rainwater erodes cracks until the plateau is split into two parts by a canyon. The mesa is the wide, flat-topped rock that becomes separated from the plateau.
31 Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: BUTTE (a small, isolated, flat-topped mountain) - this starts as a mesa – remember this is a flat-topped mountain with a cap of hard rock. Rainwater seeps down the side of the mesa, eroding the softer rock found underneath the hard rock cap. The softer rock is eroded from the sides which retreat inwards. Eventually there is no rock to support the hard rock cap which falls away leaving a tall, thin spire of rock – a butte.
32* Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: • It helps to remember that each landform is linked – they form from each other in a particular order: • A plateau has a layer of hard rock on top of soft rock. This is called cap rock. • Rainwater erodes cracks in the plateau to form a canyon which is open at both ends. • The mesa is the resulting rock that is separated from the plateau. • Rainwater then seeps down the side of the mesa and erodes the softer rock. • The sides retreat inwards and eventually the hard cap rock falls away leaving a thin spire of rock – butte.
33* Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: A wadi is a steep-sided, deep, flat floored (dry) valley/gully in a desert. Usually they do not have any water in them. There may be a few desert plants in a wadi. Steep sides Flat bottom • After heavy rain, water follows an old river bed. • The water erodes the bed and widens and deepens it. • The water evaporates leaving a wide, flat floored valley containing deposited rocks – the wadi. Loose material Some plants
34* Extreme Environments Hot Desert Environments What are hot desert landscapes like? Landforms created by water erosion: A wadi is a steep-sided, deep, flat floored (dry) valley/gully in a desert. Usually they do not have any water in them. There may be a few desert plants in a wadi. The material in the wadi is often loose. Therefore, when there is a flash flood, lots of material in the wadi is transported (moved) & then deposited (dropped) further down the valley.
Process: • Weathering – causes the decay and disintegration of rock: • exfoliation • free-thaw • salt-crystallisation • hydration • The rock is weakened and exposed to erosion. 35 Extreme Environments Hot Desert Environments What are hot desert landscapes like? The physical processes of weathering, erosion, transportation and deposition form distinctive hot desert landforms – remember that you could be asked to link processes and landforms:
Remember that there are also 3 methods of transportation of material – traction, saltation and suspension - eventually material that has been transported is laid down/dropped – this is the process of deposition and this also leads to the creation of hot desert landforms: SAND DUNES. 36* 5m – 30m high Crescent shaped Upwind slope - 15º Downwind slope - 34º Horns face downwind and can be up to 100m apart Occur singly or in groups
37* Extreme Environments Hot Desert Environments What are hot desert landscapes like? A barchan dune has a particular shape. It is a crescent shape with ‘horns’ pointing downwind. The upwind slope is approx 340 & the downwind slope is approx 150. Barchan dunes occur where there’s a limited supply of sand, therefore they may by up to 100m apart. They form around an obstruction. A prevailing wind picks up sand - suspension. The obstruction then causes the wind to lose speed/energy & deposit the sand, which causes a greater obstruction & more material is deposited. They will move over time = marching/migration. air is diverted around the dune – as deposition occurs horns are formed.
38 Extreme Environments Hot Desert Environments What are hot desert landscapes like? The process of deposition also leads to the creation of hot desert landforms: SALT PANS. • After flash floods, water ponds are left on the desert floor. • The rainwater is unable to drain through rock so remains on surface. • Due to really hot temperatures the water evaporates leaving salts on the surface. • These accumulate over 1000’s of years into a mass of white salt.
Extreme Environments 39 Hot Desert Environments What do we know about hot deserts and how have they been represented in cultural resources? • You need to have knowledge of one named hot desert environment – the Sahara Desert. • The Sahara is in North Africa – it extends across a number of countries including Algeria, Libya, Morocco and Mali. • The Sahara Desert – population density. • Covering 3.5 million square miles and having only 2.5 million inhabitants, the Sahara has one of the lowest population densities on earth – roughly 1 person per square mile. • Higher population densities are found where food and water sources are available and where the climate is not as harsh. • The majority of people living in the Sahara are nomads – moving from region to region in search of better living conditions.
40* Extreme Environments Hot Desert Environments How do people use hot deserts? Hot deserts are used by a variety of people for different reasons. The Bedouin The Bedouin are pastoral (raise animals – herding camels, sheep, goats and cattle) nomads (they move around from place to place looking for fresh pasture for their animals). They live in the Sahara in North Africa - they overcome problems in the following ways: Water – They plan routes from water source to another, travelling deeper into the desert in the winter when there is some rain, and staying close to reliable water sources in the summer. Also, use other indicators such as lines of plants and birds/insects to find hidden underground water. Transport – Bedouins traditionally use camels as transport as they are able to carry large loads and walk long distances. Lighting a fire Clothing - They traditionally wear woollen, loose-fitting clothes, from their animals. These insulate against the heat of the day & provide warmth at night. Covering their bodies, allowing air to circulate means that the amount of sweating is reduced, therefore reducing dehydration. Head-cloths/burkas are used to keep out heat, cold, wind and sand. Shelter–They need to be able to carry their shelter with them & pack up quickly. Their tents are made from goat hair cloth as it is warm at night, windproof & waterproof. They are long/narrow with roll-up sides allowing breeze to blow through in the hot day.
41* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? • Hot deserts pose many challenges to different groups of people - The Bedouin • Bedouins have found it difficult to survive in the modern world – many have given up their nomadic lifestyle and have moved to live in cities – many traditional cultures have died out due to rural to urban migration - the following are all push factors – reasons why people want to leave an area – in this case the Sahara Desert: • nomadic herding of camels/goats is a subsistence (growing enough food to feed yourself and your family)lifestyle - it is difficult to produce food as there is not enough good pasture for animals – this can be made worse by: • drought – this is caused by lack of water over a long period of time – pasture is destroyed, animals die and crops also fail – dehydration impacts on people and animals (e.g. cattle) - this can lead to: • famine – large numbers of people are not able to access food/water causing malnutrition, starvation and death. • there are government restrictions on the nomad way of life – stopping the Bedouin from moving freely in search of water and pasture. • global warming is making the desert environment more extreme – hotter temperatures and longer dry periods. • Bedouins are attracted to cities close to the desert like Tobruk (a seaport in Libya) – they are attracted by pull factors – these include jobs, healthcare, educational opportunities, housing and availability of food. • However, adapting to city life can be difficult, especially with little money – unemployment amongst Bedouin people in cities like Tobruk is high as only a few obtain educational qualifications. There are often culture conflicts between people following a more European/urban lifestyle and Bedouin people who struggle to keep in touch with their heritage.
42* Extreme Environments Hot Desert Environments How do people use hot deserts? • Indigenous people (Bedouins in the Sahara) have positive and negative impacts on the environment: • POSITIVE – Bedouins have adapted to live with the desert environment: • they manage their use of water – adapting their movements to find more water (e.g. travelling further into the desert in the winter when there is some rain). • their nomadic lifestyle means that the desert is allowed to recover after they have used a certain area and moved on. • they don't build permanent structures that could damage the desert ecosystem.
43* Extreme Environments Hot Desert Environments How do people use hot deserts? Indigenous people (Bedouins in the Sahara) have positive and negative impacts on the environment: NEGATIVE – POPULATION PRESSURE - There are increasing numbers of people living in regions such as the Sahel to the south of the Sahara. This has been due to high birth rates, falling death rates and migration from the surrounding areas. With more people to feed, farmers are growing crops on land that is only just suitable for farming (marginal land). When there were less people land could be left fallow – time was given for soil to regain nutrients – but now they use the soil more frequently causing desertification.
44* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? Desertification This is the process by which land turns into desert. After a drought land will often recover. Desertification is when the land is so damaged that it can’t recover. The damage can be caused by physical (natural) processes, or by human (due to people) processes. One of the areas at risk of desertification is the Sahel, in Africa. It is on the southern edge of the Sahara. It is an area where some farming occurs & is mainly grassland.
45* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? • Desertification - physical causes: • Less rainfall – Overall, there has been a reduction in the amount of rain in the Sahel over the last few years. • Less reliable rainfall – Also, the rain is less reliable – it may be many years before its rains properly in an area. • Higher temps –This increases the amount of moisture/water lost through evaporation & transpiration (water given off by plants). • Land becomes degraded (permanently damaged) – scientists believe that climate change/global warming has made this worse. Desertification - human causes: • Irrigation – water for growing crops is quickly evaporated, salt in the water is left on the ground = unsuitable for future farming. Groundwater is used up. • Over-grazing – Herds of animals eat lots of vegetation. Too many animals means that the vegetation cannot recover – soil is exposed to erosion. • Over–cultivation – Soil can’t recover from lots of farming. It loses it nutrients and becomes weaker – soil will not bind together and loss of vegetation means that it blows away. • More people - Many people in the Sahel use firewood. More people means too much may be collected - plants cannot recover – vegetation is lost and there are no roots to bind the soil together so it is exposed and eroded away by wind and rain.
46* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? • Desertification – what are the effects/impacts: • people cannot grow food – they may starve or are forced to move to new land to grow food (this then starts the cycle of desertification again). Young people often migrate away – the farming is very hard work for those left behind – the nomadic way of life is dying out. • people cannot graze animals – people cannot sell their animals and lose money. Cattle need to travel for days to find grazing land – animals produce very little milk for people to use. • wild animals suffer because they are forced to change their habitat and move elsewhere to find food. They might not be adapted to their new surroundings and find it difficult to survive. • there are less rivers for fishing or for water for people/animals to drink. • land becomes hard and compact – flash floods occur after a heavy rain as water can’t sink into the ground – this impacts on the homes of people and animals.
47* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? • The challenge of desertification can be managed in a variety of ways: • Desertification – solutions – sustainable farming methods: • Here are some sustainable methods that have been successfully tried in the Sahel to restore farmland: • Stop over-grazing – reduce the number of animals grazing to allow vegetation to grow back. • Integrated farming – keep animals and grow crops – animal manure is used to fertilise soil and to help crops grow. • Plant more trees (afforestation) – trees protect soil from wind and rain. Tree roots help to bind soil and prevent erosion. Only branches are cut off existing trees. • Store water – build earth dams to collect water in the wet season. Stored water is used to irrigate crops in the dry season. • These methods have been particularly successful at Machakos in Kenya.
Extreme Environments 48 Hot Desert Environments What do we know about hot deserts and how have they been represented in cultural resources? Hot desert environments have an impact on humans: • The Sahara Desert – economic activity. • Agriculture (farming) – irrigation can transform deserts into fertile areas where crops can be grown and houses can be built. Irrigation is used in the Sahara to bring land into agricultural production to support rising populations. Modern drip irrigation is currently being used to halt starvation. Irrigation – the artificial supply of water to the land to help crops to grow.
49* Extreme Environments Hot Desert Environments How do people use hot deserts? Hot deserts can provide valuable energy resources – extraction of oil and gas to provide fuels for export: General Beneath the Sahara are layers of sedimentary rock. Oil and gas are trapped within them after they were formed from the remains of microscopic organisms millions of years ago. Positives Exporting oil and gas can make a lot of money for multi-national companies and countries. Negatives The money isn’t distributed equally in the country & multinational companies are based in overseas countries. It is very expensive to find, extract Oilfield drilling rig and transport oil and gas. Many of the larger, easy to find oil reserves have now been used up. Transporting oil and gas through pipelines is very expensive. Oil & gas are non-renewable resources – one day they’ll run out & burning them releases CO2.
50* Extreme Environments Hot Desert Environments What challenges do hot deserts pose to people and how can they be overcome? • Hot deserts can provide valuable energy resources – extraction of oil and gas to provide fuels for export: • Case study – drilling for oil at Hassi Messaoud in Algeria: • from oil rigs they drill down hundreds of metres into the rock to obtain oil and gas (challenge – the cost of extracting oil is high; managed by – multinational companies like Shell and BP make the necessary investment). • the base is deep within the desert (challenge – access/transport is difficult; managed by – workers travel in and out by plane – there is a landing strip nearby). • 40,000 people work at the oil plant (challenge – not enough food & lack of drinking water leads to dehydration; managed by – underground water is pumped up and food supplies are flown in). • the oil plant is isolated – the oil needs to be taken to where it is needed (challenge – transporting oil is difficult ; managed by – pipelines carry the oil hundreds of kilometres to Mediterranean ports on the North African coast). • Also: challenge – excessive heat makes working conditions difficult & the lack of roads making accessibility difficult means that workers have to stay in the desert for long periods; managed by – living accommodation for 40,000 has been constructed and work carries on through the night when it is cooler (also meaning that more oil can be extracted and exported = more income).