The Coastal Risk Atlas tool is designed to support evidence-based decision-making for climate adaptation, disaster risk reduction, and coastal zone planning by integrating high-resolution datasets related to coastal hazards, exposure, and vulnerability. Built on the risk assessment framework established by the Intergovernmental Panel on Climate Change (IPCC), the Atlas conceptualizes coastal risk as a function of three interacting components: hazard, exposure, and vulnerability.

Spatial Framework and Resolution

The tool is structured using a standardized grid system with cells measuring 1 km by 1 km. This resolution provides sufficient detail to capture localized risk while allowing for meaningful comparisons on a regional scale.

The spatial extent of the analysis is limited to areas situated below 30-meter elevation contour, which are most vulnerable to coastal hazards such as flooding and erosion.

Data Integration and Sources

The development of the Coastal Risk Atlas relied on the integration of multiple geospatial datasets representing the three core components of coastal risk: hazard, exposure, and vulnerability. These datasets were sourced from open-access platforms and processed to ensure consistency in spatial resolution, extent, and coordinate systems prior to analysis.

Hazard Data

Hazard data are primarily derived from two pre-existing tools on The ROC: the Sea-Level Rise Insight Tool and the EroTrack Tool. The Sea-Level Rise Insight Tool provides simulated inundation layers based on projected sea-level rise scenarios. EroTrack Tool on the other hand generate shoreline dynamics and coastal erosion trends along the West African coastline.

Exposure Data

Exposure data focused on identifying the human and ecological elements located within hazard-prone areas. Gridded population density data were obtained from the WorldPop project (https://www.worldpop.org/), while land use and land cover data which includes the spatial distribution of critical ecosystems such as mangroves and wetlands were sourced from the ESA WorldCover dataset (https://esa-worldcover.org/en).

Vulnerability Data

Vulnerability data were also drawn from WorldPop and supplemented with national and regional statistics. Socioeconomic indicators such as income levels, educational attainment, and housing quality were used to represent the underlying fragility of communities.

Data reflecting community dependence on coastal and marine ecosystems, particularly in fishing-dependent communities, were also considered. In addition to these indicators, other such as access to early warning systems, disaster response infrastructure, and health services were compiled.

Risk Assessment Framework

A structured risk assessment framework was used to quantify coastal risk at the grid-cell level. First all the indicators for hazard, vulnerability and exposure were normalized onto a uniform range, between 0 and 1.

Within each component, weighted indicators were aggregated to generate a composite score, resulting in individual hazard, exposure, and vulnerability indices for each 1 km grid cell.

For the final Coastal Risk Score, the model applied a formula in which the hazard index was multiplied by the average of the exposure and vulnerability indices. The resulting risk scores were then visualized as heatmaps to depict the intensity and spatial distribution of coastal risk across the landscape. These scores were further categorized into low, medium, and high-risk zones to facilitate interpretation and support decision-making.

Technical Implementation

The final spatial outputs (hazard, exposure, vulnerability, and composite risk layers) were published from ArcGIS Pro as feature services through an ArcGIS Server environment.

Each feature service was assigned to a unique API endpoint, enabling seamless integration into The ROC datahub website. The web interface was developed using Esri Leaflet through CodePen for rapid prototyping and deployment.

Users on The ROC datahub website can explore coastal risk data of the west African countries by toggling between hazard, exposure, vulnerability, and composite risk layers. Grid cells on the map are clickable, providing detailed information about the contributing indicators and risk scores for each location.

Validation and Sensitivity Analysis

To ensure the reliability and credibility of the Coastal Risk Atlas, a validation and sensitivity analysis process was undertaken. Validation involved cross-checking the model outputs with available historical data on observed coastal impacts, such as flood events, shoreline retreat, and community-level erosion reports.

In areas where ground-truth data were available, for instance data from Lower Volta feasibility study, the model's predictions were compared with historical incidents of flooding, infrastructure damage, and community displacement. This comparison helped confirm that high-risk zones identified in the Atlas corresponded with locations that had experienced significant coastal hazards in the past.