Coastal flood risk (Aqueduct 3.0)

Source: WRI Aqueduct 3.0 Year: 2019 Category: Physical risks · Mitigating services · Climate Acute Risks Coverage: Global Format: Boundary polygons (sub-national assessment units) Used in risk analysis: No (contextual layer; not used in materiality scoring)

What it shows

This layer estimates the share of the population that can be expected to be affected by coastal flooding in an average year. Rather than picturing the worst conceivable flood, it expresses an annual-average impact, which makes it a useful screening signal for where coastal flooding is a persistent, material risk to people and the assets around them.

How it is built

The indicator is drawn from the World Resources Institute's Aqueduct global water-risk framework. Coastal flood risk is assembled from three components: the hazard (inundation caused by storm surge), exposure (population located in the flood zone) and vulnerability (susceptibility of that population and its assets to harm). The existing standard of flood protection is also folded into the calculation, so that areas with stronger defences carry a correspondingly lower expected impact. The result is the "expected annual affected population": impacts from rare, extreme flood years are averaged together with more common, milder years to give a single representative figure per assessment unit.

How to read it

Higher values mean a greater proportion of the local population is expected to be affected by coastal floods in an average year, signalling higher risk. Lower values indicate limited expected impact. Because values are reported per polygon, a site falling within a high-value coastal unit should be treated as exposed and reviewed further.

Class thresholds

The underlying quantity is a physical-impact rate: the expected annual share of the local population affected by coastal flooding — a dimensionless probability (affected people per person per year), reported per sub-national assessment unit (cfr_cat). The six mapped categories map to the following thresholds on that share:

This layer is contextual and is not used in materiality scoring, so it carries no risk-flag threshold of its own.

How these thresholds were set. The class split follows the WRI Aqueduct coastal-flood-risk methodology, which already folds hazard, population exposure, vulnerability and the prevailing standard of flood protection into the expected-annual-affected-population figure before binning. The exact derivation of the break values is set in the Aqueduct methodology and is not re-documented here.

Reference: WRI Aqueduct — wri.org/aqueduct.

Source

Aqueduct (World Resources Institute). WRI Aqueduct global water-risk framework — https://doi.org/10.46830/writn.23.00061.

Comparison with the WWF Risk Filter Suite

This maps to WWF Biodiversity Risk Filter indicator S3_7 Flooding (and the Water Risk Filter B3 Flood category). WWF expresses flooding as a basin-level composite of occurrence and hazard; Darwin instead provides a population-impact flood-risk surface that already incorporates exposure, vulnerability and existing flood protection. The two are aligned on the underlying hazard but differ in how the risk is expressed.

Legend

Symbolised field: Coastal Flood risk category

Generated from darwin/layers/layer-coastal-flood-risk-aqueduct-3-0.toml and risk_indicator_pairs.toml (develop).