Task 1:Place each of the following deserts on the map: (use a pencil if unsure) • Atacama desert • Australian desert • Sahara desert • Patagonian desert • Arabian desert (cold) • Kalahari desert • Mohave desert • Namib desert • Gobi desert (cold) • Great basin Soil: • They are immature as they are constantly blown away by strong winds. • There is little organic matter due to little vegetation. • They are often very saline (salty) due to capillary action. • Known as arid soils. Temperature: • Deserts have extreme temperatures and tend to have a large annual range. • Some go from -40°C in winter to +40°C in summer. • Large diurnal range (difference between day and night temperatures). • No cloud cover so deserts heat up during the day but heat escapes at night. Flash fact: The hottest temperatures ever recorded were 58°C in the Libyan Desert and 57°C in Death Valley! Rainfall: • Rainfall is irregular and erratic. • It may not rain for many years (e.g. 60 years in Arica, Atacama Desert). • Annual rainfall may occur in one single downpour. • Flash floods occur due to hard baked soil rather than infiltration taking place. Flash: must remember … • Semi arid: less than 500mm rain/year • Arid: less than 250mm rain/year • Hyper arid: less than 100mm rain/year Vegetation and animal life: • Deserts support very little in the way of vegetation or animal life. • NPP (net primary productivity) tends to be around 90g per square metre per year compared with 2200g in the rainforest. • Desert plants have to be xerophytic (withstand dry conditions) and halophytic (withstand salty conditions). • Animals have had to make special adaptations to survive. Wind: • Winds in the desert tend to be strong, often blowing at over 60km/h. • They tend to be local and seasonal, such as the ‘Harmattan’ in the Sahel or the ‘Sirocco’ in Morocco. • There is very little shelter and flat land allows wind speed to accumulate. • The dry, unconsolidated soil can cause huge dust storms to form. Population: • Very few people live in the desert and population density tends to be less than 2 per square km. • People who live away from desert settlements tend to be nomadic. • Nomads move from water source to water source, herding either cattle or goats. • Their accommodation is usually temporary e.g. tents. • They are dry and parched areas of the world which are deficient in moisture. • They cover about 33% of the worlds land mass. • They are mainly found between 10 and 30 degrees N and S of the equator. • They have insufficient rain to support high densities of plant or animal life. • They tend to have low population densities. • People who live in deserts are usually nomadic. But in order to define a desert properly, we have to consider the following: • Temperature • Rainfall • Vegetation & animal life • Human population • Wind • Soil.