Desert System Skills (AQA A Level Geography)

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Jacque Cartwright

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Geography Content Creator

Hot Desert Skills

Short answer questions

These questions only assess knowledge (AO1) and carry 4 marks each
Four clear statements are needed (not always sentences) that answer the question and shows knowledge of the topic
Examples or details are useful but not always needed
Take no longer than 5 minutes to answer these questions

Climate graphs

Climate graphs show average rainfall and temperatures typically experienced in a particular location
Temperature is shown on a line graph, and rainfall on a bar graph
They are usually represented on the same set of axes with the months of the year along the base

climate-graph-for-jeddah-saudi-arabia

An example of a climate graph for a typical hot desert region - Jeddah Saudi Arabia

Interpreting and describing climate graphs

Look at the overall shape of the graph
- Is the temperature line steep or gentle?
- Does it change throughout the year or look almost flat?
Look for extremes
- Quote the highest and lowest temperature and rainfall and the month in which it occurs
- Remember to quote units, eg celsius or millimetres
- Identify the seasons when most or least rain falls
- Or when the highest and lowest temperatures are experienced
Work out the temperature range by subtracting the lowest figure from the highest figure
Add the rainfall totals for each month together to work out the total annual rainfall

Worked example

Describe the climate of Jeddah, Saudi Arabia

[4 marks]

climate-graph-for-jeddah-saudi-arabia

The climate here is arid, as precipitation is 79 mm per annum [1]
Temperature range is mostly constant throughout the yea r[1]
The average annual temperature is 28.1 °C with summer high of 32.4 ‘C in August and winter low 24.6°C in January [1]
The driest months are May to Sept with zero mm of rain [1]
Wettest months are Oct to April, with a high of 26mm in Nov and a low of 2.6 mm in Feb [1]

Data response questions

All carry 6 marks and assess skills (AO3)
'Analyse' is the frequent command word
Knowledge development is not needed to explain the data and will not gain credit (just waste time)
Simple or obvious statements will gain minimum marks
Always look for patterns/trends/ranges
Identify anomalies or countertrends
Re-work the data - find percentages, mean, averages, range etc.
Use qualitative descriptive words - do not just copy from the resource
Make connections and draw relationships between different sets of data provided (compare and contrast)
Question or critique the data relationship or the data itself
Take no longer than 9 minutes to answer these questions

Data stimulus questions

Carry either 6 or 9 marks and assesses topic knowledge and ability to apply that knowledge to other situations (AO1 and AO2)
Question will usually ask for 'own knowledge' as well as a general understanding of the resource
Refer to the data provided, but also use the resource as an access route to demonstrate your own knowledge and understanding and how it applies to the wider concept of the resource
Use the same approach for data response and be prepared to make a judgement (assess)
Take no longer than 9 minutes for 6 marks or 12 minutes for 9 marks

Worked example

Figure 4 shows a landscape in the Namib Desert in southern Africa.

Figure 4

fig-4-paper1-nov2021-aqa-alevel-geography

Note: The landforms in this landscape are aligned approximately north-west to south-east and extend from between 16 km to 32 km in length, reaching heights between 60 metres to 240 metres. The sediment source is the Orange River, several kilometres away.

Using Figure 4 and your own knowledge, assess the relative importance of factors leading to the development of this landscape.

[6 marks]

Answer:

These are barchan dunes and the major factors in the development are these dunes are that they need ready supply of available sediments, which in this case is fine and coarse sand [1]. There needs to be a regular, consistent prevailing wind, which is shown in the figure running from northwest to southeast [1d].
There needs to be a smooth flat surface over which the wind can blow the sand, but also some subtle changes in the shape of the land so that sediments can collect [1]. The figure shows patches devoid of sand, but also irregularities on the surface, which would allow the sand to caught and build up [1d].
These three factors work together and that without a supply of sand from the Orange River, the barchans could not form [1]. Furthermore, a less reliable and consistent wind direction would quite quickly alter the shape of the dunes [d]. Finally, without the flat surface, sand would not be able to move and the figure shows clear evidence that sand has been completely removed from most places on the north west side of each dune [1d]. Without such flat surfaces the sand could not move so freely and the barchans could not establish such a recognisable shape [1d].
There is an equal inter-relationship between these factors which has shaped the barchans as shown in the figure. [1]

Exam Tip

Extended 9 mark questions are found only in the optional element and assesses AO1 and AO2.
You must show and highlight connections across the specification (synopticity) and relate it to the question.
Do not spend longer than 13 minutes and aim to write between 250 and 350 words.

Scatter graph

Points should not be connected
The best-fit line can be added to show the relations
Used to show the relationship between two variables
- In a river study, they are used to show the relationship between different river characteristics such as the relationship between the width and depth of the river channel

Strengths	Limitations
Clearly shows data correlation	Data points cannot be labelled
Shows the spread of data	Too many data points can make it difficult to read
Makes it easy to identify anomalies and outliers	Can only show the relationship between two sets of data

scattergraph

Scatter graph to show the Relationship Between Width and Depth on a River Long Profile

Types of correlation

Positive correlation
- As one variable increases, so too does the other
- The line of best fit goes from the bottom left to the top right of the graph
Negative correlation
- As one variable increases the other decreases
- The line of best fit goes from the top left to the bottom right of the graph
No correlation
- Data points will have a scattered distribution
- There is no relationship between the variables

Percentage and percentage change

To give the amount A as a percentage of sample B, divide A by B and multiply by 100
- In 2020, 25 out of 360 homes in Catland were burgles. What is the percentage (to the nearest whole number) of homes burgled?
- $25 \div 360 \times 100 = 6.94 [t o n e a r e s t w h o l e n u m b e r] = 7 %$

A percentage change shows by how much something has either increased or decreased
$P e r c e n t a g e c h a n g e = \frac{f i n a l v a l u e - o r i g i n a l v a l u e}{o r i g i n a l v a l u e} \times 100$
- In 2021 only 21 houses were burgled. What is the percentage change in Catland?
- $\frac{21 - 25}{25} \times 100 = - 16 %$
- There has been a decrease of 16% in the rate of burglaries in the Catland area
Do remember that a positive figure shows an increase but a negative is a decrease

Statistical Skills

This is the study and handling of data, which includes ways of gathering, reviewing, analysing, and drawing conclusions from data

Percentage and percentage change

To give the amount A as a percentage of sample B, divide A by B and multiply by 100
- In 2020, 25 out of 360 homes in Catland were burgles. What is the percentage (to the nearest whole number) of homes burgled?
- $25 \div 360 \times 100 = 6.94 [t o n e a r e s t w h o l e n u m b e r] = 7 %$

A percentage change shows by how much something has either increased or decreased
$P e r c e n t a g e c h a n g e = \frac{f i n a l v a l u e - o r i g i n a l v a l u e}{o r i g i n a l v a l u e} \times 100$
- In 2021 only 21 houses were burgled. What is the percentage change in Catland?
- $\frac{21 - 25}{25} \times 100 = - 16 %$
- There has been a decrease of 16% in the rate of burglaries in the Catland area
Remember that a positive figure shows an increase but a negative is a decrease

Mean, median, mode and range

Mean = average value (all the values added and divided by the number of items)
Median = middle value when ordered in size
Mode = most common value
Range = difference between the highest value and lowest value

Sample site	1	2	3	4	5	6	7
Number of pebbles	184	90	159	142	64	64	95

Taking the example above to calculate:
Mean - $\frac{184 + 90 + 159 + 142 + 64 + 64 + 95}{7} = \frac{798}{7} = 114$
Median - reordering by size = $64 64 90 [95] 142 159 184$ = 95 is the middle value
Mode - only 64 appears more than once
Range - $184 - 64 = 120$

Upper, lower and interquartile range

These are the values of a quarter (25%) [lower quartile (LQ)] and three-quarters (75%) [upper (UQ)] of the ordered data

No. of shoppers	2	3	6	6	7	9	13	14	17	22	22
			Lower quartile			Median			Upper quartile

The interquartile range (IQR) is the difference between the upper (UQ) and lower quartile (LQ)
It measures the spread (dispersion) of data around the median
A large number shows the numbers are fairly spread, whereas, a small number shows the data is close to the median
UQ - LQ = IQ [ $17 - 6 = 11$ ]

Standard deviation

This measures dispersion more reliably than IQR and the symbol for it is 'σ' (sigma)
The formula is $σ = \sqrt{\frac{Σ {(x - \bar{x})}^{2}}{n}}$
Σ means 'sum of' and $\bar{x}$ is another way of writing 'mean' and 'n' is the number of samples taken
Work out individual aspects of the formula first e.g. the mean
Sample results:

Sample site	1	2	3	4	5
Number of pebbles	5	9	10	11	14

Calculate the mean - $(5 + 9 + 10 + 11 + 14) \div 5 = 9.8$
Calculate $x - \bar{x}$ for each number
Square each of those values (the square of a negative number becomes positive)
Add the squared values to give $Σ (x - \bar{x})$
Divide the total by 'n'
Finally, find the square root

$x$	$\bar{x}$	$x - \bar{x}$	$(x - \bar{x})$
5	9.8	-4.8	23.04
9	9.8	-0.8	0.64
10	9.8	0.2	0.04
11	9.8	1.2	1.44
14	9.8	4.2	17.64
$Σ$ = 42.8

$σ = \sqrt{\frac{42.8}{5}} = 2.93 (2 d p)$
Numbers closely grouped around the mean shows a small deviation
A large standard deviation would show a set of numbers that were spread out

Spearman's rank correlation coefficient

A test to determine if two sets of numbers have a relationship
Not the easiest to calculate
Σ means 'sum of', $d$ is the difference and 'n' is the number of samples taken
The formula is $r_{s} = 1 - \frac{6 \sum d^{2}}{n^{3} - n}$

Rank each number in both sets of data, with the highest number given rank 1, second highest 2 etc.
Calculate 'd' which is the difference between ranks of each group e.g. ranks for group 5 are 4 and 6; difference will be 2
Square value 'd' and calculate the total $d^{2}$ to find $\sum d^{2}$
Finally, calculate the coefficient of $r_{s}$ using the above formula
The resulting number should always be between -1 and +1

GNP ($) per capita and Life Expectancy (years)

Country	GNP	Rank	Life Expectancy	Rank	$d$	$d^{2}$
1	15,124	5	73	5	0	0
2	20,535	4	72	6	2	4
3	10.432	9	68	8	1	1
4	7,050	11	62	11	0	0
5	22,950	3	76	3	0	0
6	14,800	6	75	4	2	4
7	23,752	2	77	2	0	0
8	36,875	1	79	1	0	0
9	5,525	12	61	12	0	0
10	8,678	10	66	9	1	1
11	12,211	8	65	10	2	4
12	13,500	7	70	7	0	0
$n = 12$		$Σ d^{2}$ = 14

$Σ d^{2} = 14 a n d n = 12$ .
$r_{s} = 1 - \frac{6 \times 14}{12^{3} - 12} = 1 - \frac{84}{1716} = 1 - 0.048951 (0.05) = 0.95$
(0.048951 can be rounded to 2 decimal places giving 0.05)

A positive result shows a positive correlation, where one variable increases so does the other
The closer the number is to 1, the stronger the positive correlation
A negative results shows a negative correlation, where one variable increases the other decreases
The closer the number is to -1 the stronger the negative correlation
If however, the correlation is 0 or near to 0, there is no relationship

Determining significance

Spearman's rank may show that two sets of numbers are correlated, however, it does not show how significant the link between the two values are
To check for significance; a table of critical values or a graph is needed
This looks at the probability of the links occurring by chance
A 5% or higher probability of chance is not significant evidence for a link
1% or less is a significant evidence of a link
This is the significance level of a statistical test
The degrees of freedom needs calculating - $n - 2$
- Using the example above: $12 - 2 = 10$ degrees of freedom
- As $r_{s} = 0.95$ then the correlation has a less than 1% probability of being by chance
- Therefore, there is a high significance level of a relationship between GNP and life expectancy

Spearman’s Rank Correlation Significance Table

Degrees of Freedom	5% (0.05)	1% (0.01)
8	0.72	0.84
9	0.68	0.80
10	0.64	0.77
11	0.60	0.74
12	0.57	0.71
13	0.54	0.69
14	0.52	0.67
15	0.50	0.65
20	0.47	0.59

Exam Tip

Always check when making calculations what the question has asked you to do. Is it asking for units to be stated or calculate to the nearest whole number or quote to 2 decimal places.

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Desert System Skills (AQA A Level Geography)

Revision Note

Short answer questions

Climate graphs

Interpreting and describing climate graphs

Describe the climate of Jeddah, Saudi Arabia

[4 marks]

Data response questions

Data stimulus questions

Figure 4 shows a landscape in the Namib Desert in southern Africa.

Figure 4

Using Figure 4 and your own knowledge, assess the relative importance of factors leading to the development of this landscape.

[6 marks]

Answer:

Scatter graph

Types of correlation

Percentage and percentage change

Percentage and percentage change

Mean, median, mode and range

Upper, lower and interquartile range

Standard deviation

Spearman's rank correlation coefficient

Determining significance

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Author: Jacque Cartwright