Impacts of Sea Level Rise on Danish Coastal Wetlands - a GIS-based Analysis

Abstract

Intergovernmental Panel on Climate Change (IPCC) scenarios run by an ensemble of models developed by the Coupled Model Intercomparison Project (CMIP) projects an average sea level rise (SLRs) of 0.6 to 1.2 m for the low and high emission scenarios (SSP1-1.9, SSP5-8.5), during the next century (IPCC 2021). The coastal zone will experience an increase in the flooding of terrestrial habitats and the depth of marine productive areas, with potential negative consequences for these ecosystems. The coast in Denmark is highly modified due to anthropogenic uses. Dikes, dams, and other coastal infrastructure are widespread, causing a coastal squeeze that prevents natural coastal development and inland migration of coastlines. We performed a national-scale analysis on the impacts of mean sea level rise (MSLR) in 2070 and 2120, and a 1 in 10-year storm surge water level (10SS) in 2120 MSLR for the Danish coast. Our study shows extensive permanent flooding of coastal habitats (~14%), whereas only 1.6% of urban areas will be flooded. Finally, very large agricultural areas (~191,000 ha) will be frequently flooded by 10SS if no extra protective measures are planned. With the present coastal protection structures, key habitats will be affected by permanent flooding or coastal squeeze while even larger extents will be subjected to intermittent marine flooding. About 45% (199 km²) of all Danish coastal wetlands will be permanently flooded by 2120, while areas occupied by forest, lakes and freshwater wetlands will be more frequently flooded by marine water. This study highlights the importance of including coastal habitats as dynamic elements in climate adaptation plans. Conservation and restoration of key habitats such as coastal wetlands should be prioritized in management plans. If Denmark does not change its current priorities, it may face the complete loss of coastal wetlands habitat in the 22nd century.

Keywords: Climate change; Coastal flooding; Coastal meadows, Salt marshes; Coastal nature; Danish national Spatial plans; Sea level rise.

Fig. 1

Distribution of §3 and Natura 2000 coastal wetlands in Denmark, 2020. The six selected pilot Danish municipalities are highlighted in light gray

Fig. 2

Methodology conceptual diagram. Estimated flooding scenarios here represented by 2120 were calculated using SCALGO live flooding model. The estimated flooding was overlaid on different land uses, hereby represented by Natura 2000 distribution. The resulting map shows land uses which will be flooded by 2120. *Coastal protection structures consist of diverse human infrastructure such as dikes, locks, pumping stations etc

Fig. 3

Vertical distribution of coastal wetlands in 6 Danish municipalities. Elevation reference Danish Vertical Reference 1990 (DVR90)

Fig. 4

Projected change of coastal wetlands (CM) in 6 municipalities in 2120, after average MSLRs

Fig. 5. Present and predicted 2120 distribution of coastal wetlands in Nordfyn, Denmark.

The selected area A is Fjordmarken, a drained area reclaimed from the sea more than 150 years ago. Area B will be in coastal squeeze by 2120. C is an area with potential for vertical migration for coastal wetlands by 2120

Fig. 6. Existing coastal wetlands (coastal meadow) at Fjordmarken, Nordfyn, Denmark. (Photos by Paula Canal-Vergés).

A Dike between Odense fjord and the area of "Fjordmarken". B Coastal meadows north from the drained channel. C Coastal meadow south from the drainage channel. D Drainage channel. E Rotational agricultural land, reclaimed from the sea.

Fig. 7

Predicted future coastal wetlands (coastal meadows) in Nordfyn municipality after sea level rising by 2120, with and without the removal of coastal protection structures