Combined effects of high water level and precipitation on flooding of Gothenburg, Sweden

Abstract:
In the future, both rising sea water level and higher precipitation are expected due to climate change. Gothenburg is one of the cities in Sweden most affected by flooding in urban areas. Flooding is caused by very high sea level, but also as a consequence of heavy rainfall over the city. It is unknown whether high sea level or heavy rainfall is the most important reason for flooding, or if the combination of them causes the most severe flooding. Flooding caused by combinations of extreme water levels and rains in Gothenburg, are simulated using Mike21 for two scenarios: present climate and year 2100. A digital elevation model is used as input together with water level data from the harbour (Torshamnen) and CDS-rainfall (Chicago Design Storm). In present climate, extreme rainfall and extreme sea water level give more or less the same amount of flooding. If a greater part of Gothenburg is taken into account, extreme precipitation is expected to be the most important factor. In year 2100, the area along the harbour is flooded more severely by a 100-year water level, as the level of the quay is exceeded. In future climate, flooding from sea surge will cause more severe flooding.