ORRAA - Coastal Risk Index

Methodological Description

This part of the Coastal Risk Index project focuses on physical risks, using globally consistent model results of present and future extreme sea levels (ESLs). The index is based on a study that aims to assess the potential impacts of coastal flooding on global scales under current and future climate conditions. It focuses on extreme sea levels (ESLs) and how they are expected to change by 2030 and 2050 due to factors like sea level rise, tides, and storm surges. Future projections are based on the worst-case climate scenario and consider various return periods, which indicate how often certain flood levels are likely to occur.

Flood modelling was done using a reduced-physics method to accurately simulate how water would flow over land during a flood, while considering surface roughness. This approach is more reliable than simpler methods but requires more computing power. The models used high resolution global digital elevation data to generate flood maps, covering large stretches of coastline, and included adjustments in the forcing to account for important natural features like mangroves and reefs, which can help reduce flood risks.

To account for the presence of flood protection infrastructure, a new dataset was developed representing global flood protection levels. This dataset estimates how protected different coastal areas are based on factors like income, population density, and the presence of ports or airports. In some regions, this dataset was augmented with more detailed local data.

The study assesses the impact of flooding on both populations and assets, using global datasets to estimate how many people and how much economic value are at risk. Flood risks were calculated for different scenarios with and without natural ecosystems, and for two time horizons (2030 and 2050), which allowed the study to quantify the benefits of conserving or restoring natural barriers.

There are some limitations to our approach, such as not fully accounting for future land subsidence or future changes in coastal protection infrastructure. Additionally, future extreme weather events like tropical cyclones could make the impacts of coastal flooding even more severe, which wasn't fully captured in the present study's models. Therefore, the projected flood risks are considered to be on the lower end of what might actually occur in regions affected by this type of storms.