1. WATER CYCLE 1 : system concepts
Mass balance
Inputs
Outputs
Stores
Flows
We are grateful to Hodder for their permission to use the diagrams in this resource.
WJEC Focus Box 3.1.1
Eduqas Focus Box 2.1.1

2. Water Cycle 1 System components
Stores are natural reservoirs of water, such as the ocean, lakes or ice caps
A water flow entering a store is called an input: for example a river entering the ocean
Flows leaving stores are called outputs: for example, evaporation of ocean water
Flows are movements (or transfers or fluxes) between stores in a system
Inquiry question: What are the main elements of a system?
Students discuss the concepts, such as stores and flows, using prior knowledge from KS3/4
Students discuss open systems (with flows across its boundary e.g. an ecosystem) and closed systems (global water cycle)
Class activity
What is the difference between an open system and a closed system? What examples are there of each?

3. Water Cycle 1 The global water cycle
The global water cycle is shown as a ‘black box’ model
What are the strengths and weaknesses of viewing water stores and flows in this way?
Inquiry question: What are the main elements of the global water cycle?
Class activity
What systems have you studied in other Geography topics? What are their similarities and differences?
(c) Hodder Education [OCR A-level Geography (Raw)]

4. Water Cycle 1 Another view of the water cycle
Inquiry question: What are the main elements of the global water cycle?
Students discuss the usefulness of different system diagrams, and system theory
Class activity
Which illustration of the water cycle do you prefer, and why?
(c) Hodder Education [Edexcel A-level Geography Book 2 (Dunn)]

5. Water Cycle 1 The concept of mass balance
At a global scale, mass balance means that the total amount of water is always conserved
At the global scale, there is a fixed amount of water in the Earth-atmosphere system (about 1385 million cubic kilometres of water)
Transfers can occur; changes occur in where water is stored without affecting the mass balance. For instance, water vapour in the atmosphere is precipitated on to the land as rain or snow after condensation occurs: although it has changed state, all water still remains in the system
Inquiry question: What is meant by mass balance of a system?
Class activity
What other water transfer processes are there?
Why don’t they affect the system’s mass balance?

6. Water Cycle 1 Global water stores
Volume
(cubic km)
Per cent of
total water
Distribution and characteristics
Oceans
1,335,000 97
Oceans cover two-thirds of the Earth
Cryosphere
26,000 2
Ice and snow stores found at high latitudes (poles) and high altitudes
Groundwater
15,000 1
Can remain stored for 10,000 years
River and lakes
178
0.01
Uneven distribution due to climate
Soil moisture
122
Permafrost in Russia and North America
Atmosphere 13
<0.01
There is sufficient moisture for ten days of rain in the atmosphere
Biosphere
0.6
Distributed unevenly because of climate
Inquiry question: How do different global water stores compare in terms of their size, distribution and characteristics ?
Discussion of students’ prior knowledge (where applicable) of water stores, including the cryosphere and groundwater stores.
Discussion can focus on how local geological factors affect groundwater storage; climate affects biomass size and water storage.
Develop quantitative skills by comparing the importance of the different stores in the table.
Class activity
(1) Compare the size of the different stores (2) What local factors affect water storage in different places?

7. Water Cycle 1 Investigating the cryosphere
These are areas of the Earth where water is present as snow or ice
This includes ice sheets, ice caps, alpine glaciers, sea ice and permafrost
Inquiry question: How do different global water stores compare in terms of their size, distribution and characteristics ?
Discussion of students’ prior knowledge (where applicable) of the cryosphere e.g. glacial landscapes; cold environments; tundra ecosystems
Class activity
Which other Geography topics require you to have knowledge of the cryosphere?
(c) Hodder Education [AQA A-level Geography (Skinner)]

8. Water Cycle 1 Water store changes
Global hydrological stores change in size over time (seasonal or longer-term)
Both physical and human factors can play a role
For instance, water stored in the Aral Sea has declined markedly since the 1990s
Inquiry question: How and why have water stores changed in the past, or are changing now?
Discussion of students’ prior knowledge of possible reasons for the Aral Sea shrinking e.g. over-use by agriculture and industry; increasing aridity (possibly linked with climate change). NB introduce the Aral Sea using a map if students have no prior knowledge.
Class activity
What factors could explain the changing size of the Aral Sea?
(c) Hodder Education [Edexcel A-level Geography Book 2 (Dunn)]

9. Water Cycle 1 Ice accumulation and ablation
Accumulation is the build-up of snow and ice which takes place within the cryosphere
Ablation is the change from solid ice to liquid or water vapour when temperature rises above 0°C. This wastage of surface snow or ice is achieved by melting and evaporation (the change from ice to vapour is called sublimation)
Inquiry question: How and why have water stores changed in the past, or are changing now?
Discussion of students’ prior knowledge of accumulation and ablation (if they studied glacial landscapes in Year 12)
Class activity
Use the RGS-IBG interactive resource to explore system changes involving ice accumulation and ablation:

10. Water Cycle 1 Changes over time in the cryosphere
Seasonal variations in ice accumulation and ablation bring cyclical fluctuations in water flows and storage in glaciated regions such as the Tibetan plateau
Many cryospheric waters stores are expected to undergo a permanent reduction in size on account of anthropogenic (human-induced) climate change
Longer-lasting changes have occurred naturally in the distant past, including the arrival and departure of glacial and inter-glacial epochs
There are periods in Earth’s past when the planet is believed to have been entirely ice-free
Inquiry question: How and why have water stores changed in the past, or are changing now?
Discussion of students’ prior knowledge (where applicable) of past glacial epochs. Most A-level Geography textbooks will give a sound account of this. Alternatively, use:
A starting point for further independent research into changing water and ice storage:
If time allows, the ‘snowball earth’ film:
Class activity
Research (1) Snowball Earth Cryogenian ice ages and (2) Hothouse Earth conditions when the poles were ice-free

11. Water Cycle 1 Rapid and local transfer processes
A monsoon is an especially wet season
In Mangalore in southwest India, more than two-thirds of the year’s rainfall falls in three months
During the monsoon, rapid water transfers from the atmosphere to the land can take place in just hours or minutes
Inquiry question: How is an appreciation of time and scale important for the study of water flows and transfers?
Group/pair research work reviewing personal experiences of high rainfall; or looking online for recorded maxima.
Class activity
What is the greatest intensity of rainfall you have ever seen? How much rain can fall in an hour?

12. Water Cycle 1 Slower global transfer processes
Long-term anthropogenic climate change is projected to impact on water transfer processes globally
Major water transfers from land to the ocean - and accompanying sea level rise - would follow if the Greenland and Antarctic ice sheets were to melt
Together, they contain more than 99 per cent of the freshwater ice on Earth. If the Antarctic Ice Sheet melts, sea level will rise by a further 60 metres
However, this would take thousands of years
Inquiry question: How is an appreciation of time and scale important for the study of water flows and transfers?
Students discuss prior knowledge of sea-level rise e.g. thermal expansion
Class activity
What is the current rate of global sea-level rise and why is it happening?

13. Flows in and out of stores are called inputs and outputs
Water Cycle 1 Plenary
The global water cycle is a closed system in which all water is conserved over time (mass balance)
Flows in and out of stores are called inputs and outputs
Lakes, oceans, the atmosphere, vegetation, soil and groundwater are water stores, along with the cryosphere (the largest global store of fresh water)
The relative size of ocean and cryosphere storage has altered considerably in the past
Anthropogenic climate change may lead to further changes
Rapid water transfers and storage changes can occur over shorter time scales too, for example the monsoon