Evaluating Future Flooding Risks by Including Wave Height Distributions in Short- and Long-Term Sea Level Variations

Assessing sea flood risks has a focal role in future coastal planning as global sea level rise is evident in the changing climate. Ability to safely plan and build coastal areas is essential and to support this, we need to evaluate the sea level changes for the next 100-200 years.

Both short- and long-term sea level changes must be considered when compiling sea level scenarios. In our study, short-term sea level changes, mainly caused by wind and air pressure in the Baltic Sea region, are based on 30 years (1982-2011) of data from the 13 tide gauges located on the Finnish coast. The long-term mean sea level scenarios comprise three factors: global sea level projections adjusted for the Finnish coast, regional land uplift and total water balance of the Baltic Sea. The coastal effect of the sea level is always affected also by the wave conditions, which may vary greatly along the coast.

Instead of determining separately the compensation for wave action and summing the maximum sea level and maximum wave height components together, we use location-specific probability distribution approach. This method is a new tool for evaluating high sea level jointly with high wave height, and can be exploited in the Baltic Sea coasts and also beyond it. We aim to extend and improve the existing Baltic Sea assessment, previously carried out in 2014, to evaluate future flooding probability levels for the Finnish coast.

Firstly, our calculations give estimates of the occurrence of rare sea levels by combining short- and long-term sea level variations up to 2100 for the whole Finnish coastline. Secondly, for the same period of inspection, we evaluate the joint effect of sea level and waves at certain locations on the southern coast of Finland, where individual wave measurements are available.