Hazard systems: cascades, probability and resilience
Analyse interacting hazards and vulnerabilities, interpret return periods and evaluate resilience across time.
A-level study: check your qualification and chosen options below.
Trace a cascading hazard
A primary process can trigger secondary processes: shaking may destabilise a slope or disrupt utilities, and damaged transport can delay response. Cascades connect physical and social systems.
Multi-hazard settings involve overlapping hazards and sometimes interacting responses. A protective measure for one hazard can create exposure to another.
Worked example
In a fictional region, shaking damages a substation, interrupting pumps and hospital supply. The chain identifies a mechanism; it does not quantify every resulting loss.
Common mistake: A cascade is not established by listing several hazards.
Interpret risk and return periods
A return period is a long-run recurrence estimate under specified assumptions. A 1-in-100 annual exceedance event has an estimated 1% probability in any one year under the model.
The event can occur in consecutive years. Changing climate, land use and records can alter estimates; uncertainty is especially large for rare events.
Worked example
With an independent, constant 1% annual probability, fictional 30-year probability of at least one exceedance is 1 − 0.99³⁰ ≈ 26%. These assumptions must be stated.
Common mistake: A 100-year event is not scheduled once each century.
Evaluate resilience and recovery
Resilience involves capacities to prepare, absorb disruption and recover or adapt. Compare service continuity, livelihoods and unequal recovery, not only visible rebuilding.
Governance, trust, wealth and access influence capacity. International response can help while also creating coordination or dependency challenges.
Worked example
Fictional electricity service returns for 90% of customers in ten days, while 40% of displaced households remain without permanent housing six months later. The indicators concern different systems and timescales.
Common mistake: One rapidly restored service cannot establish complete recovery.
Try a different resource
Hazard and exposure overlays
The occupied-home count represents exposure. Hazard and vulnerability categories are ordinal labels; multiplying them does not produce a probability of loss. A screening rule is supplied for this fictional exercise.
Scroll the diagram sideways to see the full resource.
| District | Hazard category | Occupied homes | Vulnerability index (ordinal 1–3) |
|---|---|---|---|
| A | High | 180 | 1 |
| B | Medium | 70 | 1 |
| C | High | 90 | 2 |
| D | Low | 180 | 3 |
Resource description
A: High hazard, 180 occupied homes, vulnerability index 1; B: Medium hazard, 70 occupied homes, vulnerability index 1; C: High hazard, 90 occupied homes, vulnerability index 2; D: Low hazard, 180 occupied homes, vulnerability index 3. The vulnerability index is ordinal, not a probability.
Write an explanation
Check your answer
- Connect hazard processes to exposed systems.
- Compare vulnerability and response capacity.
- Use comparable outcomes and timescales.
- Evaluate governance alongside physical conditions and infrastructure.
Practise and review a written answer
Case studies
Tōhoku earthquake and tsunami, 2011 · Nepal earthquake, 2015 · Haiti earthquake, 2010
These pages provide selected evidence. Check the whole case requirement with your teacher.
Read further
- www.aqa.org.uk — source or course reference
- www.aqa.org.uk — source or course reference
- qualifications.pearson.com — source or course reference
- www.ocr.org.uk — source or course reference
- www.eduqas.co.uk — source or course reference
Hazard, exposure and vulnerability · Plate motion and tectonic hazards · Association and geographical explanations
Course links
AQA A-level Geography · Pearson Edexcel A-level Geography · OCR A-level Geography · Eduqas A-level Geography
Next topics
Tectonic hazards: explain the different impacts · Global governance and the Antarctic commons
Selected teaching sequence with fictional worked data. The linked case records supply bounded evidence; they do not satisfy every course case requirement.