Data analysis : predicting the coastal change rates of the sandy Dutch North Sea coastline in different sea level rise scenarios for the years 2050 and 2100

The climate of planet Earth is changing, and the effects of human induced climate change can have a significant impact on the safety of coastal regions due to increased erosion by extreme weather and Sea Level Rise (SLR). It is uncertain how the sandy Dutch North Sea coastline will be affected by SLR as result of climate change. The International Panel on Climate Change (IPCC) defined four climate change scenarios and the Joint European Research Centre (JRC) used two of these scenarios (RCP4.5 & RCP8.5) to produce probabilistic SLR scenarios. This study aims to determine how the probabilistic SLR scenarios of the JRC will affect the shoreline of the sandy Dutch North Sea coastline and estimate the cost of maintaining the coastline of 2018 till 2100. This contributes to a safer and more resilient coastline and the understanding of the effects of climate change on the sandy Dutch North Sea coastline. Using the approach of this study is a plain and low-cost solution for managers to execute an initial estimation of coastline erosion and costs to maintain a coastline. The results can be helpful for coastal managers to determine whether and where coastal protection would be necessary based on predicted erosion. A data analysis based on historical coastal measurements and satellite data was used to determine the historical movement of the Dutch North Sea coastline. Additionally the Bruun Rule was used to predict the coastal recession rates for the years 2050 and 2100 under RCP4.5 and RC8.5 based on the yearly coastal topography/bathymetry measurements of the Dutch North Sea coastline in 2018 (JarKus), SLR predictions and cross-shore sediment transport trends. Lastly a Life Cycle Costing Analysis was carried out to estimate the costs of maintaining the coastline of 2018 till 2100 in multiple SLR scenarios. The results showed that the historical movement of the Dutch North Sea coastline has an average of +0.25 m/yr (range -3.5 and +4 m/yr) for the period 1970 - 2017. Predicted SLR results in coastline recession and depending on which 95th percentile SLR scenario was used, the recession could be as much as 0.49 – 4.54 m/yr (2050) to 0.45 – 6.64 m/yr (2100) under RCP 4.5 (low values) and RCP8.5 (high values). Statistical analysis found a significant difference in coastline recession between the three main coastal areas: Wadden, Holland, and Delta. It is unknown how the coastal profile will change due to SLR. The Dutch government will have to replace 2.2 – 4.4 million m3 and 11.7 - 62.7 million m3 of lost beach volume due to SLR for respectively 2050 and 2100 for under RCP 4.5 (low values) and RCP8.5 (high values). Replacing the volumes that might be lost by predicted SLR could cost the Dutch Government between 3.7 – 7.4 million EUR/year (2050) to 61.8 – 331.1 million EUR/year (2100) extra under RCP 4.5 (low values) and RCP8.5 (high values). Future change rates of the sandy Dutch North Sea coastline, based on SLR predictions, will have a more landward trend compared to the changing rates of the last five decades; hence more erosion will take place. The costs of maintaining the coastline of the year 2018 in 2100 (372 M EUR) could be as high as nine times the costs of the year 2018 (41 M EUR).EU Horizon 2020 research and innovation programme under grant agreement No 727277 through Deltares