6.3 Local and global resilience

A composite flood risk map combines four layers: hazard (flood probability/magnitude), exposure (population and assets in the hazard zone), vulnerability (capacity to cope, e.g. housing quality and income), and capacity/resilience (proximity to shelters, drainage, and early warning). Risk is highest where hazard, exposure, and vulnerability all coincide and capacity is weakest.

The delta neighbourhood has: (1) high hazard — it lies on a flood-prone delta; (2) high exposure — dense informal housing places many people in the zone; (3) high vulnerability — informal construction with weaker materials; (4) some capacity — evacuation drills exist, but drainage is limited. Three of four risk-elevating conditions are strongly present.

When hazard, exposure, and vulnerability all coincide, the composite overlay produces a high-risk rating. The evacuation drills contribute to capacity but do not sufficiently offset the three converging risk factors, so the area maps as high risk.

The correct answer is that high hazard likelihood combined with high exposure and high vulnerability, with only modest capacity offsetting them, produces a high-risk classification. This is what a GIS composite overlay is designed to reveal.

The question tests understanding of how a composite risk map differs from a simple hazard map — specifically, that risk requires the coincidence of hazard, exposure, and vulnerability, moderated by capacity.

The option 'High hazard likelihood only, since physical flooding potential is the dominant variable' describes a hazard map, not a risk map. A risk map explicitly combines social and physical layers, so this option conflates the two concepts and is incorrect.

The option 'High vulnerability only, since informal housing materials determine risk independent of flood frequency' isolates one layer. Vulnerability alone does not produce high risk if the hazard probability or exposure is low — all layers must be considered together.

The option 'High exposure only, since the density of people automatically creates the highest risk' makes the same error in reverse — exposure without hazard or vulnerability does not automatically generate the highest risk classification. A crowded city on stable, unflooded ground is not high-risk.

The only option that correctly reflects composite risk-map logic is the first: high hazard + high exposure + high vulnerability, partially offset by some capacity. This matches how GIS overlays are used to produce a colour-graded composite risk map.

A hazard is a natural event with potential to cause harm; risk is the likelihood of harm actually occurring to people and assets. Risk requires both a hazard and exposed, vulnerable elements. Without exposure and vulnerability, there is no risk to map, even if the hazard is severe and frequent.

The island has a very high hazard score (frequent, high-magnitude lava flows) but zero exposure (no permanent population) and zero vulnerability (no buildings, no livelihoods at risk). Multiplying any hazard score by zero exposure yields zero risk — the island should be in the lowest risk category.

The student has confused a hazard map with a risk map. Shading purely by hazard frequency is a common mistake — it produces a map of where hazards occur, not where harm is likely. A composite risk map must incorporate exposure and vulnerability layers.

The correct response is that the claim is incorrect because no exposed population means composite risk is low, and the island should map as green/low-risk, not red/high-risk.

The question tests the critical distinction between a hazard map (physical event location and magnitude) and a risk map (harm potential requiring exposure and vulnerability).

This option endorses the student's mistaken assumption that a risk map is the same as a hazard map. Composite risk maps explicitly require exposure and vulnerability data — hazard frequency alone cannot determine the final risk rating.

Lava flow is absolutely a standard, mappable natural hazard used in GIS risk-mapping worldwide (e.g. Hawaii, Iceland). Rejecting the claim on these grounds is factually wrong and irrelevant to the actual error being made.

This option repeats the same error as option two — it equates hazard magnitude with risk. A composite map assigns high risk only where hazard coincides with high exposure and vulnerability, which is absent on an uninhabited island.

The only logically sound response is the first: zero population = zero exposure and vulnerability, so composite risk is low and the island should be green/low-risk. This correctly applies the hazard-versus-risk distinction central to risk mapping.