Water and Physical Geography (AQA A Level Geography)
Revision Note
Written by: Robin Martin-Jenkins
Reviewed by: Bridgette Barrett
Climate and Water
The quantity and quality of water available to people depend on a number of physical factors
Climate has a significant influence on the water supply
Precipitation
Temperature
Wind speed and direction
Physical Factors Affecting Water Supply
Aspect of climate | How it influences water supply | Examples |
|---|---|---|
Precipitation | Levels vary seasonally and regionally Reliable rainfall needed to maintain supplies Seasonal differences mean storage needed to ensure a year-round supply The global average is 860mm per year but only 23% falls over land | Arica, in Chile, has the lowest recorded average rainfall of any city in the world at 0.8mm per year Saudi Arabia has the lowest figure for any region, at 66mm per year |
Temperature | Higher temperatures mean greater rates of evapotranspiration and potential drought Extreme cold can lock water supplies up in ice and snow in winter months, making it less accessible | Average temperatures in central Saudi Arabia can reach 38℃ in summer 8 of the 37 settlements in Greenland have water supplies classed as poor |
Wind | Onshore winds bring more humid air over land whereas offshore winds lead to aridity in coastal areas More wind can contribute to higher rates of evapotranspiration and humidity | Phoenix, Arizona, USA has the lowest average annual wind speeds at 6.2mph contributing to low humidity and an average rainfall of 200mm per year |
Examiner Tips and Tricks
Try and remember a real life example for each factor, such as the ones in this table. This will enable you to back up the points you make and your answers will become rooted in real geography. This will give you more marks for the ‘knowledge and understanding’ element which makes up roughly half of all the marks in your A level.
Geology and Water
The structure and characteristics of the rock underlying a landscape can influence the distribution of groundwater stores
Layers of rock that contain groundwater are called aquifers
They need rocks with high porosity or permeability to hold underground water and allow the aquifer to be recharged, e.g.:
Chalk
Limestone
Sandstone
Gravel
Aquifers can be a reliable source of water because they are:
Not subject to evaporation
Springs and wells give an even supply throughout the year
Not affected by uneven seasonal rainfall
Water filtered through bedrock is purer; needs less treatment before drinking compared to reservoir or river water
But aquifers can be vulnerable to overuse and the improper disposal of chemicals on the surface
Falling groundwater levels may indicate climate change or over-abstraction
Over-abstraction occurs when the rate of extraction of water from the aquifer is greater than the recharge rate
It can lead to a number of serious environmental impacts including:
Subsidence
Loss of wetlands and reduction in vegetation
Drying of soils leading to dehydration of crop roots
Lower water table
Rivers drying up
The saltwater incursion into groundwater
The Thames Basin aquifer, in the south-east UK, has a good example of an ‘artesian’ aquifer below it:
Boreholes are now up to 200m deep
There is not high enough hydrostatic pressure to power fountains
The main supply of water within London and the Thames basin is from underground chalk aquifers
Water is accessed directly through boreholes, supplying 20% of London’s water supply
London’s aquifer water levels have dropped in recent years
The population of south-east UK continues to increase
Demand for water is rising further
Risk of over-abstraction leading to depletion of the aquifer
Examiner Tips and Tricks
Although it is unlikely you will get asked to draw diagrams in your A level geography exam, a quick labelled or annotated sketch, such as the one on this page, can be really effective, saving time and space, so feel free to use this method and you will be credited for it. Just remember to refer to the diagrams in the written part of your answer so that the two link up.
Drainage and Water
The size and nature of a river’s drainage basin can influence water supply in the surface storage system
The larger the basin the larger the catchment area for inputs into the system via precipitation
Impermeable soils and bedrock in the basin support more overland flow and lead to a denser tributary network
A dense network of tributaries allows falling precipitation to reach the main channel quicker, keeping the river levels higher
This may be offset by greater rates of evaporation, depending on the climate and season
Basins that are less dense allow more infiltration into [popover id="DUoOIPfl7osGfJEU" label="groundwater"] stores
The Thames Basin provides 80% of London’s water supply from tributaries that flow over impermeable clay
The relief within a drainage basin can also influence the water supply
Gentle or undulating relief means water passes more slowly through an area and there is greater time for it to infiltrate and contribute to groundwater
Steep relief generates faster flow and the reverse effect
Undulating relief is more likely to generate natural lake storage than the other two extremes of very mountainous or very flat relief
The type and amount of vegetation in the drainage basin can also influence the water supply
Vegetation can intercept rainfall, impede surface flow and absorb water through root systems
This affects the amount of collectable water stored on the surface
But it can also transpire water, keeping the atmosphere moist and helping rain clouds form increasing the inputs into the basin
Examiner Tips and Tricks
If asked a question about physical geography and water supply, be sure to note how the various factors link together. For example, the size and number of rivers in an area depends on climate, geology, relief and vegetation.
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