A Level Geography - Water Notes

The Water Cycle and Water Insecurity
Contents
The Importance of the Global Hydrological Cycle..................................................................................1
The Drainage Basin................................................................................................................................3
The Hydrological Cycle on a Local Scale.................................................................................................5
Deficits within the Hydrological Cycle..................................................................................................10
Surpluses within the Hydrological Cycle..............................................................................................19
The Impact of Climate Change on the Hydrological Cycle...................................................................25
The Causes of Water Insecurity...........................................................................................................29
The Consequences and Risks of Water Insecurity................................................................................35
Managing Water Supply......................................................................................................................44


The Importance of the Global Hydrological Cycle

The Hydrological Cycle on a Global Scale

 Systems approach
 balance of inputs, outputs & movements within a system
 3 concepts
1. Stores – reservoirs where water is held e.g. oceans
2. Fluxes – rate of flow between stores
3. Processes – the physical mechanisms which drive the fluxes of water between the
storms

The Global Hydrological Cycle

 Driven by solar and gravitational potential energy
 Closed system
o total volume of water constant and finite
o no external inputs or outputs
 water can exist in different states
o proportions held in each state varies
 Ice Age
o more water held in cryosphere in solid form
o less held in oceans i.e. stores
o sea levels dropped considerably (over 140m lower than today)
 Recent climate warming is beginning to reverse this with major losses of ice in Greenland
and Antarctica


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The Water Cycle and Water Insecurity

,  On a small scale humans built water storage reservoirs to compliment natural lakes to
increase water supplies
 Blue Water
o stored in rivers, streams, lakes & groundwater
o liquid form
o visible hydrological cycle
 Green Water
o stored in soil & vegetation
o invisible part of hydrological cycle


Store Percentage of Volume Residence Time
Oceans 96.9% 36000 years
Cryosphere 1.9% 15,000 years (depending on
size)
Groundwater 1.1% 10,000 years– deep water
100 to 200 years –shallow
water
Rivers & Lakes 0.01% 2 weeks to 10 years
50 years for v. large scale
Soil Moisture 0.01% 2 – 50 weeks
Atmospheric Moisture 0.001% 10 days




Temporal Scale & Accessibility in the Hydrological Cycle

 Residence Time
o Average length of time a water molecule spends in a store
o impact turnover in water cycle system
o
 Fossil water
o ancient, deep groundwater former in pluvial periods (wetter climate
o e.g. below Sahara desert
o not renewable or reachable
 Ice sheets store water for long periods
o some of water in Antarctic is over 800,000 years old
 Most accessible water for human use e.g. rivers & lakes
o shorter residence times
o open to the driving forces of hydrological processes e.g. lost through evaporation
 Longer residence time = increased vulnerability to pollution
 Accessible water for human use


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The Water Cycle and Water Insecurity