High-Resolution Coastal Disaster Risk Assessment: A Case Study of Korea

The Korean government has revised the Coastal Management Act to conduct annual coastal disaster risk assessments. These assessments aim to identify the causes of coastal disasters and respond to them effectively. They provide scientific and quantitative risk information on vulnerable coastal areas, preparing for increased coastal disaster damage due to sea-level rise, typhoon intensification, and climate change.

In this study, the coastal disaster risk assessment framework was established by applying the IPCC AR6 (2023) framework. Indices and indicators suitable for the Korean coastal system were selected. To incorporate the concept of 'Response' emphasized in IPCC AR6, 'Reduction factors' were introduced to 'Vulnerability'. The Coastal Disaster Risk Index (CDRI) was evaluated by considering three factors: 'Hazards', 'Exposure', and 'Vulnerability'. Data for the evaluation were collected from statistical and basic data authorized by the Korean government. A high-resolution spatial grid of 100 meters was established, and evaluation results for each indicator and index were produced through statistical analysis. The results are displayed in five grades within the coastline (evaluation line) and coastal area (evaluation grid) after verification and validation. The 25 indicators and 31 basic data for coastal disaster risk assessment were updated with the latest data, and new databases were built for some indicators.

In conducting coastal disaster risk assessments, extreme analysis of external forces (Hazards such as rainfall, wind, surges, and waves) that cause disaster damage was performed to evaluate the possibility of disaster occurrence. The recurrence frequency was applied to the grade interval criteria, which were set based on the 50-year or 100-year recurrence frequency, referring to the design criteria of various external forces. To evaluate indicators with different units and sizes, a non-dimensionalization process called standardization (converting values between 0 and 1 using cumulative probability distribution) was performed. Weights for each indicator were applied to calculate the weighted average, and the 'Hazards', 'Exposure', and 'Vulnerability' indices, along with the CDRI, were calculated. In the CDRI, results of each indicator and index were displayed in five grades from 1 to 5. Grade 5, indicated as "High risk" (red), was the most dangerous, and grade 1, indicated as "Low risk" (green), was the safest.

As a result of the evaluation, Busan Metropolitan City and Jeju Island showed dangerous results with an average of grade 4. Since the evaluation results are a high-resolution spatial grid evaluation with a size of 100 meters, the distribution of risk grades by grid within each local government is well distinguished. The spatial distribution of coastal disaster risk areas is expressed more accurately than visualizing them as a "line" on the coastline. The results of the 'Exposure' and 'Vulnerability' evaluations showed a safe grade in grids with low population density or low density, such as residential complexes and industrial complexes. Therefore, the results of this study can provide realistic and detailed information to local government officials who need to make decisions on designating coastal disaster risk areas and establishing reduction measures.