Study the climate graph for Alice Springs, Australia. When is the hottest month? How hot is it? When is the coldest month? How cold is it? What is the temperature range? (The temperature range is calculated by subtracting the lowest temperature from the highest.) When is the wettest month? How wet is it? Are there any months of drought? Is there a relationship between temperature and rainfall?

ACTIVITY

1. In 1922 the temperature recorded in El Azizaia, Lybia was a) 48°C b) 58°C c) 68°C?

2. Where is the driest place on earth? a) The Atacama Desert b) The Sahara Desert or c) The Mojave Desert?

Where are they located?The hot deserts of the world are located between 15° and 30° north or south of the equator. This is a zone of subsiding or sinking air. Air that rises due to the intense heat at the equator divides to fl ow north and south. When it reaches 15° to 30° it begins to sink because it has lost so much of its heat. This sinking air creates a zone of high pressure. As the air is sinking, no clouds can form and a lack of clouds means these areas are very dry.

Hot deserts – what are they and where are they?

Figure 1 Location of the worlds’ deserts

1. Arica in Chile went without rain for 14 years?

DID YOU KNOW?GET STARTED

What is the climate like?

In Death Valley California the hottest temperature recorded was 54°C. What was the coldest temperature recorded (in Celsius)?

RESEARCH LINK

Figure 2 Climate graph for Alice Springs

10 OCR GCSE Geography

Diurnal range: daily range in temperature

Flash fl ooding: sudden local fl ood resulting from heavy rain

Cumulonimbus clouds: low altitude, tall clouds with a fl at base and fl at top that occur during thunderstorms.

FLASH FLOODINGSo we know why the deserts are so dry. How then can we explain the photograph on the right? The Mojave Desert is clearly fl ooded. Flash fl ooding can occur in deserts due to convectional rainfall. During the day the ground gets very hot. The ground heats the air above it and this forces the heated air to rise. This heated air cools and condenses as it rises. Eventually large, black, cumulonimbus clouds form and it rains. The rain is often in the form of a thunderstorm. Flooding occurs because the ground has been baked hard by the sun and the large storm raindrops cannot infi ltrate the impermeable surface of the desert. The rains run across the ground as surface run-off and causes fl ooding.

Why are these areas so hot?It’s all to do with proximity to the equator. Look at Figure 3 below. Rays A and B are rays of sunlight. Ray A is striking the earth at a location similar to that of the UK. Ray B is striking the earth at the hot desert areas. Ray B has to heat a small area of ground and so the heat is very concentrated. Due to the way the earth is curved, ray B has to heat a larger area and so the heat is much more dispersed and not as intense. In addition ray B has to travel further. This means it gets weaker and collects dirt on the way, therefore it is not as strong on arrival.

Variations in climateThe Diurnal range is much greater than the annual one. In the Atacama Desert the day is 25°C hotter than the night. Why is this the case? On the previous page you learned that due to sinking air there are hardly any clouds in the desert. Clouds can refl ect up to 80% of sunlight. In the absence of clouds the ground gets very hot during the day. At night however, this heat is lost rapidly because there are no clouds to trap the heat in. This results in a large diurnal range and sometimes produces a frost at night.

Figure 4 Flash fl ooding in the Mojave desert

Figure 3 Incoming solar radiation

KEY WORDS

• Explain why you might take the following things to Alice Springs with you: umbrella, sun cream, woolly hat.

ACTIVITY

Hot deserts are environmentally sensitive areas. Should tourism be allowed?

THINK ABOUT IT

Hot deserts – what are they and where are they? 11

1. Study the climate graph below

3. Describe and justify the equipment you would take on an expedition to a hot desert region [6]

1. Study the climate graph below

GradeStudio

matches sunglasseswalking boots hatsun cream water

The candidate is probably quite pleased

with this answer. There are 6 marks and they

have listed 6 items. However, as a rule, if

your answer looks like a shopping list you

are not going to score the highest marks.

The candidate has ignored the word ‘justify’

in the wording of the question. If the word

‘justify’ appears, the examiner wants an

explanation of why you have chosen those

items eg: you would need a hat to protect

your head from the hot sun.

Graph A

05

10152025303540

Jan F eb Mar Apr May Jun Jul Aug S ep Oct Nov Dec

Months

Tem

pera

ture

in

degr

ees

C

0510152025303540

Rain

fall

in m

m

R ain

Temp

How do you know this is a hot desert region? [4]

Candidate A I know this is a hot desert region because it is hot and quite dry.

Candidate B

This is a hot desert. In July the temperature is 35oC and it never drops below18 oC. It is very dry. The annual rainfall total is only 110mm and between May and November there are only a few millimetres of rain.

2. Describe a landform found in a hot desert region [3]

A wadi is a desert landform. They occur in deserts they are formed when it is wet. The heavy rain follows an old river bed and erodes it even deeper.

The examiner says: The candidate has made

a common mistake. This answer is true but is

not what the question is asking. There are no

marks for explaining how the wadi formed.

The marks are only for describing what a wadi

looks like.

Which answer is the best? What makes it a better answer? Why is it a good answer?

ACTIVITY

Over to you, DESCRIBE a landform that is found in a hot desert

ACTIVITY

1. Can you give reasons why the candidate chose those 6 items?

2. Can you think of other items that you think are more important?

ACTIVITY

“Describe” suggests that you need to use lots of adjectives e.g. deep, wide etc.

HINT

12 OCR GCSE Geography

4. Higher tier and foundation papers often ask similar questions but in very different ways. Look at the example below.

Foundation Tier Higher Tier

In the space provided, name the hot desert region you have studied

a) describe one way in which people have used this regionb) Explain one positive outcome of its usec) Explain one negative outcome of its use. [8]

How do people make use of desert regions? What are the consequences of this use? [8]

Foundation tier candidate answer

a) Hot deserts are used by tourists

b) This is good because the area gets money and people get jobs

c) The desert sand gets eroded.

The examiner says: This answer would

probably score 4 marks. Look at the comments

below. There is a lot more the candidates could

say by developing their answer.

You could say what they are doing e.g. on

desert safaris, or for extreme sports

Does the area get money? Who gets the

money? And what do they do with it that

improves their lives?

What kind of jobs do people get?

How does it get eroded? Why is erosion a

problem?

Higher tier candidate answer

Hot deserts are used by people drilling for oil. This means that some areas have become very wealthy. But it also means there has been some environmental damage. The oil rigs look ugly and they can leak. This damages the delicate desert vegetation and animals.

This would probably score four marks. It’s

not a bad answer on oil but it needs another

use to get 8 marks.

Give the name of a desert where this is

happening.

Put in an example of a wealthy area.

The candidate seems to have run out of

ideas on oil. For an eight-mark question it

would be a good idea to have more than

one way in which people make use of desert

regions. It is easier to write less about two

uses than lots about one use.

Choose either a foundation or higher tier question and try to score 8 marks.

ACTIVITY

Grade Studio 13