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AS Deserts 1- Location and characteristics of hot deserts and their margins (arid and semi-arid) climate, soils and vegetation. 1.1 LocationJUN10: Distinguish between arid and semi-arid areas. (2)Arid areas receive less than 250mm of rainfall per year (1), whilst semi-arid are those areas receiving between 250 and 500mm rainfall per year (1). The semi-arid areas are found on the fringes of arid areas the deserts (1).JAN11: Describe the distribution of arid and semi-arid areas. (3) Based on map.Study Figure 7 which shows the distribution of arid and semi-arid areas.

4 (a) (i) Describe the distribution of arid and semi-arid areas shown in Figure 7. These areas mainly occur between 30 degrees north and south of the Equator. With the exception of an area in east Africa, they are not found at the Equator. They are on the western sides of continents and extend inland to varying degrees this is most limited in South America and most extensive cross North Africa, across the Middle East into Asia. The semi-arid areas are generally on the edges of the arid ones. These areas are most extensive in North Africa, Asia and Australia. 31.

JAN 13: Describe the location of areas of hot deserts (no map) (4)Hot deserts are located near to the lines of the Tropics of Cancer and Capricorn between approximately 20 and 30 north and south. They are usually found on the western side of continents such as the Atacama in South America and Sonoran Desert in North America. Sometimes, they extend the width of the continent as in the case of the Sahara in North Africa. There are no deserts present in the vicinity of the Equator. Hot deserts are present in all continents, with the exception of Europe and Antarctica. Inland if qualified. In lee of mountains.

Allow up to two for naming locations. 41

1.2 Characteristics of hot deserts and their margins (arid and semi-arid) climate, soils and vegetation. JUN09 Describe the characteristics of the hot desert climate. (4)Temperatures are characterised by large annual ranges (1) with figures to support related to location (1). Need to say more than hot - needs an appropriate figure, e.g. approx 20 to 30 + degrees C (1). Diurnal range is also high (1). 15 - 30 C (1). Very high temperatures have been recorded in the shade - upper 50s in Death Valley and Libya (1).Rainfall is low - usually defined as less than 250mm p.a.(1), but often

much lower, e.g. Death Valley averages 40mm per year (1). It is also unreliable - there may be a number of years without any rainfall (1). Often very intense, and thunderstorms when it does fall (1). Low relative humidity. Winds tend to be local and seasonal (1) e.g. harmattan (1). 4 x 1

JAN13 Study Figure 5 which shows some vegetation in a hot desert.

4 (b) (i) Describe the vegetation shown in Figure 5. (4)There are two types of vegetation clearly shown cover is sporadic. One type is a cactus (Saguaro) that stands above the other vegetation. It is mainly one large stem, with limited branches emerging from the main trunk. It is dark green in colour, but covered in white needles. The smaller shrubs (creosote bushes) have many branches which are quite thin. The leaves are plentiful, but small and light green in colour.

Allow up to 3 on either vegetation type, up to 2 for naming species shown. 41

4 (b) (ii) Explain how vegetation in hot deserts is adapted to the climate. (7)Candidates may refer back to the characteristics described in part (b)(i), but there is no requirement to do so. Relevant points from there would relate to the small leaves (and their waxy nature) to reduce evapotranspiration; the stomata on these plants close during the day, minimising water loss. The cactus is a succulent and water is stored in the fleshy stem and branches to be used during periods of dryness. Cacti have many long shallow roots allowing them to maximise intake of water during periods of rainfall. Other plants like the creosote bush have deeper roots and search for water downwards and where there is permanent groundwater. Some plants have silver coloured leaves that reflect sunlight and so plant stays cooler. There may be reference to plants that have a short growing season following rain to avoid the lack of water these may be annuals that germinate, flower, seed and die quickly or perennials that have limited bursts of activity before becoming dormant again.

Marks here are for explanation only with reference to vegetation. Level 2 (Clear) 5-7 marks

The specific features of the vegetation are linked to explanation. Explanation has a clear sequence of events, e.g. small leaves that reduce area exposed to sun and so reduce loss by transpiration. Appropriate geographical terminology is used.

TIP: Link specific characteristics to the climate such as stomata on the underside of leaves that remained closed in the day to reduce transpiration or the presence of long tap roots to reach groundwater supplies.

JUN10 04 (b) (i) Study Figure 4 which shows vegetation in Death Valley, California, an arid area.

04 (b) (i) Describe the characteristics of the vegetation shown in Figure 4.Photo shows that vegetation has small spiky leaves; yellowy/silvery leaves; low, growing shrub; evidence of spiky appearance; incomplete ground cover. Thin branches, woody.

04 (b) (ii) Explain how vegetation of arid areas is adapted to the climate.Candidates may refer back to the characteristics described in (b)(i), but there is no requirement to do so. Relevant points from there would relate to the small leaves and their waxy nature to reduce evapotranspiration; silver colour reflects sunlight and so plant stays cooler; may also refer to other features such as seeds that lie dormant.

Long roots in order to search for water; plants that store water to overcome shortage succulents; plants that have a short growing season following rain to avoid the lack of water. Marks here are for explanation only. There are no marks for describing the characteristic, though these will need to be recognised so that how the feature represents an adaptation is clear.

2- Causes of aridity atmospheric processes relating to pressure, winds, continentality, relief and cold ocean currents

JUN13: 15m: Explain two or more causes of aridity. Atmospheric pressure should relate to the positioning of many hot deserts where there is high pressure. This coincides with the positioning of the falling limbs of the Hadley and Ferrel cells. This means that air that has previously risen, cooled and become denser is now falling and is being compressed and heated as a result. Thus, rain is unlikely as it has previously lost its moisture. The air is stable; skies are clear as a result of the presence of the high pressure. Winds are affected by the presence of the high pressure. Winds blow from areas of high pressure and so winds blow out from these areas of land receiving no moisture this contributes to the aridity. For example the North East Trade winds blow across north Africa across the Sahara from about 30 degrees north. Continentality refers to the positioning of many hot desert areas away from areas of water seas and oceans and as a result the probability of rainfall is less the Sahara extends across north Africa significant distances from the Atlantic.Relief links in part to winds also in creating a rain shadow effect and contributing to aridity. For example in Australia and South America, the prevailing winds are the South East Trades. As they approach from the east, they drop their moisture in this area. This effect is exacerbated by the presence of mountains like the Snowy Mountains in south-east Australia and the Andes in South America. As winds rise to cross these, they are cooled, condensation occurs and precipitation falls on the eastern sides. Once the peaks are reached, the winds descend and are warmed, reducing the chance of rainfall and causing aridity in the Australian Desert and Atacama Desert. The scale of the area affected depends on the location of the mountains. Cold ocean currents are found off the western coast of continents moving from the poles towards the Equator should winds approach from an alternative westerly direction to that of the prevailing winds, the lower layers of the air above the cold ocean current is cooled, causing condensation and precipitation (often mist and fog) to occur over the cold ocean current. The air is then warmed as it crosses over land, so aridity is encouraged. Conclusion: There are many links between these different factors and aridity is caused by a combination of them, not one in isolation.Level 1 (Basic) (1 6 marks) Partially describes one or two causes of aridity occasional reference to terms. Points made are simple and random.Level 2 (Clear) (7 12 marks) Description of cause(s) is more specific. Begins to see sequence and make links to aridity.Level 3 (Detailed) (13 15 marks) Explanation of two or more causes is to the fore. There may be some recognition of the links between the different causes and/or the fact that it is a combination of reasons that are responsible. Sees sequence and links clearly to aridity for 2 or more.Examiners report: many students referred to all those given in the question rather than the minimum requirement and seeking depth. Most described causes separately and did not see links nor realise that it is a combination of causes that leads to aridity.

JUN12: Explain how continentality is a cause of aridity. (3)Continentality refers to areas within the interiors of land masses away from the influence of the sea. This results in winds being drier here, having lost their water content in areas nearer the sea and so increases likelihood of areas being dry and therefore deserts. There may be reference to specific winds such as north east trades over north Africa and the Sahara and dista