Storages and flows at Higher Level: The same ideas as SL. At HL, use them to explain a real problem: which flow changed, and why the boundary matters.
Practise this as you read
- Calculate a storage change from inputs and outputs.
- Justify where a boundary is drawn.
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See the whole, not one part: The systems approach is holistic: it maps every interaction, instead of studying one part in isolation.
One part at a time
- A city floods. Blame the drains.
- Bigger drains; the floods come back.
The systems approach
- Map rain, paved streets, drains, the river and farms upstream.
- Paving sends rain to the river faster: the real cause.
The same approach fits a societal system, like a city, and an ecological one, like a river basin. Most real problems are both.
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Every system has storages and flows. A mountain glacier:
| Term | Meaning | In a glacier |
|---|---|---|
| Storage | An amount of matter or energy held | Ice |
| Flow | A movement of matter or energy | Ice sliding slowly downhill |
| Input | A flow into the system | Snowfall (matter), sunlight (energy) |
| Output | A flow out of the system | Meltwater (matter), reflected light (energy) |
Storage change = inputs minus outputs: Snow adds 2.0 m of ice a year; melting removes 2.6 m. The glacier shrinks by 0.6 m a year.
A system boundary decides what is studied, in space and in time.
In space
- A fishery managed inside one country's waters.
- The fish migrate beyond it, so catches there are missed.
In time
- A wetland surveyed only in the dry season.
- The migrating birds arrive in the wet season.
Choosing a boundary: Too narrow misses a key input; too wide adds parts you cannot measure. Choose the boundary that fits the question.
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How this comes up: A short question on how the systems approach helps, or on what a figure's storages and flows show.
A coastal city now floods more often than it did 30 years ago. Outline how a systems approach could help explain why.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Keep it about the city: Tie every point to this city's storages, flows or boundary. A general definition scores little.