What does Water and Carbon Cycles cover in Eduqas A-Level Geography?

Water and Carbon Cycles is Section A of Component 2 (Global Systems and Global Governance). It studies the global water cycle (stores, fluxes, the water budget and water insecurity), the drainage basin as an open system (the water balance and storm hydrographs), the global carbon cycle (stores, fluxes and the fast and slow cycles), the role of the carbon cycle in climate (the greenhouse effect and feedbacks), and how the two cycles are coupled. It is a systems-led topic with significant quantitative skills.

How is Component 2 assessed?

Component 2 (Global Systems and Global Governance) is a written paper of 2 hours worth 110 marks, 27.5 per cent of the A level. Section A is Water and Carbon Cycles, Section B is Global Governance (migration and oceans), and Section C is the synoptic 21st Century Challenges. The paper mixes structured, data-response and extended-response questions, and the cycles section is data-rich, so calculation and graph skills (AO3) matter alongside knowledge and judgement.

What case studies do I need for the cycles?

You need at least one catchment-scale water-cycle study (a named river basin showing stores, flows and human impacts), at least one detailed carbon-cycle context (a tropical rainforest, peatland or forest showing stores, flows and human modification), and broader global examples of climate impacts and management (REDD+, the Paris Agreement, carbon capture). Strong examples include the Colorado basin and the Sahel for water insecurity, and the Amazon and peatlands for carbon.

How much maths is in this topic?

A noticeable amount. Expect to read and construct graphs (storm hydrographs, line and bar charts), calculate percentages and shares of stores, solve the water balance equation (precipitation equals evapotranspiration plus runoff plus or minus change in storage), interpret residence times, and work with carbon densities and fluxes. These are AO3 skills assessed in data-response questions, so practise calculations as well as written explanation.

What are the most common mistakes in this topic?

Calling the global water cycle or the carbon cycle open when at the planetary scale they are effectively closed (only the drainage basin is open); confusing physical and economic water scarcity; confusing the fast and slow carbon cycles; confusing positive and negative feedback; confusing mitigation and adaptation; saying greenhouse gases block incoming sunlight rather than trapping outgoing longwave radiation; and treating the two cycles as independent rather than coupled.

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Eduqas A-Level Geography Water and Carbon Cycles (Component 2, Section A): a deep dive on global systems, the drainage basin, climate and coupling

A deep-dive Eduqas A-Level Geography guide to Water and Carbon Cycles (Component 2, Section A). Covers the global water cycle and water insecurity, the drainage basin system and storm hydrographs, the global carbon cycle, the link between carbon and climate with feedbacks, and the coupling of the two cycles, with case studies, KaTeX statistics and the exam patterns Eduqas repeats.

Generated by Claude Opus 4.818 min readA110QSUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What this section actually demands
The global water cycle and water insecurity
Drainage basins and river systems
The global carbon cycle
Carbon, climate and feedbacks
The coupled cycles
How this section is examined
Check your knowledge

What this section actually demands

Water and Carbon Cycles is Section A of Component 2 and the most systems-led part of the course. The demand is to treat the water and carbon cycles as systems of stores and fluxes, to work confidently with the quantitative tools (the water balance, hydrographs, percentages of stores, carbon densities, residence times), to explain how human activity disturbs each cycle, and to understand how the two cycles couple through vegetation, oceans and the atmosphere to regulate climate. Eduqas tests this with data-rich structured questions and extended evaluations, so calculation and graph skills sit alongside process explanation and judgement.

This guide ties together the five dot-point pages for the section: the global water cycle and water insecurity, drainage basins and river systems, the global carbon cycle, carbon and climate feedbacks, and the coupled cycles. Each has its own page with practice questions; this overview shows how they fit.

The global water cycle and water insecurity

At the planetary scale the water cycle is a closed system of stores (oceans, cryosphere, atmosphere, groundwater, surface water, biosphere) and fluxes (evaporation, transpiration, condensation, precipitation, runoff). The oceans hold about $97\%$ of all water; most fresh water is locked in ice. Residence times range from days to millennia. Water insecurity arises from physical causes (low or variable precipitation, drought, depleted stores) and human causes (demand, over-abstraction, pollution, governance), distinguishing physical from economic scarcity.

Drainage basins and river systems

The drainage basin is the local open system, with precipitation input, interception, soil and groundwater stores, infiltration, throughflow and overland flow, and outputs of evapotranspiration and discharge. Its water balance is $P = E + Q \pm \Delta S$ . The storm hydrograph (peak discharge, lag time, rising and falling limbs) records the basin's response, and urbanisation, deforestation, abstraction and climate change make it flashier or alter the balance, changing flood risk and supply.

The global carbon cycle

Carbon moves between four stores, the lithosphere (largest, including fossil fuels), the oceans (largest active store), the atmosphere (smallest) and the biosphere (vegetation and soils), through fluxes of photosynthesis, respiration, decomposition, combustion and air-sea exchange. The fast cycle (atmosphere, biosphere, surface ocean) runs over years to decades; the slow cycle (lithosphere) over millions of years. Fossil-fuel combustion and deforestation move carbon from slow to fast, raising atmospheric carbon dioxide.

Carbon, climate and feedbacks

The carbon cycle regulates climate through the greenhouse effect: greenhouse gases trap outgoing longwave radiation, balancing incoming shortwave solar energy. Human emissions cause the enhanced greenhouse effect. Positive feedbacks (ice-albedo, permafrost methane, reduced ocean uptake) amplify warming towards tipping points; negative feedbacks dampen it. Mitigation (decarbonisation, sink protection, the Paris Agreement) tackles the cause; adaptation manages the consequences.

The coupled cycles

The cycles are coupled through vegetation (photosynthesis needs water; transpiration returns it), the oceans (storing both, with temperature governing evaporation and carbon solubility) and the atmosphere (carbon dioxide and water vapour are both greenhouse gases). Change propagates both ways: warming raises water vapour and cuts ocean carbon uptake, and rising carbon dioxide drives ocean acidification, so the two are best understood as one coupled climate system.

How this section is examined

A typical Eduqas profile for Water and Carbon Cycles:

Quantitative skills (AO3). Read hydrographs and store diagrams, calculate percentages and the water balance, interpret residence times and carbon fluxes.
Systems explanation (AO1). Describe stores and fluxes and explain how human activity disturbs each cycle.
Extended judgement (AO2). Evaluate mitigation strategies, or assess how far the two cycles form a single coupled system.

Check your knowledge

A mix of questions covering the whole section. Attempt them under timed conditions, then check against the solutions.

Approximately what percentage of the world's water is held in the oceans? (1 mark)
Distinguish between physical and economic water scarcity. (3 marks)
Write the water balance equation and define each term. (3 marks)
Explain why urbanisation produces a flashier storm hydrograph. (3 marks)
Name the four major stores of the global carbon cycle. (2 marks)
Explain why burning fossil fuels unbalances the carbon cycle. (3 marks)
Define the enhanced greenhouse effect. (2 marks)
Explain one positive feedback in the climate system. (3 marks)

Solutions

Q1: About $97\%$ , leaving only around $3\%$ as fresh water, most of which is locked in ice.
Q2: Physical scarcity is a genuine shortage of water in the environment (low precipitation, depleted stores); economic scarcity is where water exists but people lack the infrastructure or wealth to access and use it.
Q3: $P = E + Q \pm \Delta S$ : precipitation equals evapotranspiration plus runoff plus or minus the change in storage.
Q4: Impermeable surfaces and drains reduce infiltration and storage and increase rapid surface runoff, delivering water to the channel faster, so lag time falls and peak discharge rises.
Q5: The lithosphere (rocks and fossil fuels), the oceans, the atmosphere, and the biosphere (vegetation and soils).
Q6: Fossil fuels are part of the slow carbon cycle, locked in the lithosphere over millions of years; burning them transfers that carbon to the atmosphere in decades, far faster than slow processes can return it, so atmospheric carbon dioxide rises.
Q7: The strengthening of the natural greenhouse effect by human greenhouse-gas emissions, which trap more outgoing longwave radiation and warm the surface further.
Q8: The ice-albedo feedback: warming melts reflective ice, exposing darker ocean and land that absorb more solar energy, causing further warming and more melting, amplifying the initial change.