## 2 Study Site and Methods  
### Study Sites  
The German Baltic Sea coast is of glacial origin. The sandy sediments form long beaches and lowlands interrupted by cliffs. Most parts of the coast face strong coastal erosion and retreat. The coasts north-east of the city of Rostock are mainly only a few meters above sea level and have a very high flooding risk during storm surges (Figure 1). The many shallow coastal lagoons, the so-called \"Bodden\", cause an additional risk of flooding from the hinterland. Consequently, the entire area is very sensitive to ongoing sea-level rise. Two case study sites along the coast were selected, representing different situations: adaptation by coastal realignment and nature restoration in a rural area and hard protection measures in a touristic, built-up area.  
The first case study is the Hittelmoor, a coastal wetland of about 540 ha. With 2.1 m per year (average over the last 100 years), the coastal retreat at the Hutelmoor is the highest observed at the German Baltic Sea coast [23]. The Hutelmoor is subject to ecological restoration. At the coastline, a new coastal realignment concept was implemented. The coastline was not protected anymore and left to the natural coastal dynamics. The combined approach required coastal protection and environmental planning with links to regional spatial planning.  
The second case study is the tourism resort Ahrenshoop on the Darss-Zingst peninsula (Figure 1). In 2019, the town had only 653 inhabitants, but registered nearly 330,000 tourist overnight stays per year [24]. Tourist activities are mostly related to landscape and nature experience such as hiking, bathing, cycling, horse riding, sailing, recreational fishing and wildlife observation. Ahrenshoop is located on a strip of land between the Baltic Sea and the Saaler Bodden. It is another coastal erosion hot spot with a coastal retreat between 0.5 and 1.7 m per year and is subject to intensive coastal protection measures ([PERSON] 2019, pers.com). The study site covers an area of 2.75 km\({}^{2}\). The beaches in front of the cliffs at the  
Figure 1: The Baltic Sea region and the case study locations at the southern Baltic Sea coast, in the German federal state of Mecklenburg-Vorpommern. The case studies are the seaside resort Ahrenshoop and the Hutelmoor wetland. Areas with high risk of flooding are indicated, modified after LUNG [22].  
Baltic Sea coast are maintained by sand nourishment and hard protection. The inner coasts are protected by a dike.  
The two case studies assess different aspects of planning and have different time horizons. For Hutelmoor, four scenarios represent the development of the area from the 1980s until a hypothetical situation in 2040. The focus is on environmental and coastal protection planning in a rural area and the consequences of a new, climate-change-adapted, coastal protection approach. Ahrenshoop has a longer perspective and compares the situation today with the hypothetical situation in 2070 in an urban area with intensive tourism. Here, the focus is more on regional spatial planning aspects and the ability to deal with climate change challenges. Criteria for the case study choice was that they reflected different aspects of planning and were located in areas with the highest risk of flooding. The term scenario refers to the description of a situation, independently of whether it describes a past, the present or a hypothetical future state.