In 2007, the Swedish National Platform for Risk Reduction was set up as a part of the “Making Cities Resilient” campaign of the UN. In the campaign, cities and local governments are engage in disaster risk reduction (DRR). In Sweden, 12 municipalities participate in the project through the risk reduction platform. In the Swedish context, risk reduction usually revolves around policies and tools to prepare for and reduce the risk of a flooding. The second largest city of Sweden, Göteborg, with the largest seaport of the country has quite low elevation and is vulnerable for possible flooding caused by future sea level rise. As a participant in the “Making Cities Resilient” campaign, the municipality of Göteborg has come up with a tool that deals with the risk.
The solution consists of a GIS (Geographic Information System) tool which can simulate a flooding in the city, called the Hydromodell. It was developed by the City Planning Office and the Administration of Water together with outside consultants. The municipality financed the collection and processing of different types of data e.g. elevation, water depth and volume, flow speed, sewage infrastructure and types of urban area and surface.
The tool uses this data to simulate a flooding and to make several analyses – a risk analysis of a flood, a cost-benefit analysis of the zero alternative i.e. take no protective measures and all other alternatives with different levels of protection. With the tool, the municipality can assess which areas are vulnerable and what level of protection is required. During heavy rainfall, parameters like the capacity of the sewers is calibrated.
With the model, the municipality of Göteborg can assess which areas are vulnerable to floods, what is the probability is for a flood and what the recurrence intervals are. Additionally, the model shows the flow paths and water depth of the flood. Thanks to the model, the municipality can consider different protection and drainage measures like dikes, dams, sewage pipes and canals.
Another result of the Hydromodell is that Göteborg has extensive data on flood risks and protection measures and is gaining expertise in the field of water management. The 500 000 inhabitants of the Göteborg metropolitan area are better protected against floods or other disasters produced by heavy rainfall or sea level rise.
Göteborg has low elevation, lies at sea and has the largest river in Sweden flowing through it. This combination of circumstances forces Göteborg to take serious measure to mitigate the risk. The knowledge and expertise gained in Göteborg might prove to be of value for other cities that deal with flood risk.