In July 2011 Copenhagen experienced the worst rainfall ever with more than 80,000 homes flooded resulting in damages at a cost of around 1 billion €. A new tool has been developed in order to minimize damages from such events in the future.

Quick solution to combat effects of climate changes
With the climate changes, some regions will experience more intense rainfall. These areas will need to protect themselves from the potential damages from flooding. As a first defense the flood warning tool SURFF (Surface Flood Forecast) would be highly beneficial for most cities. Implementation of new infrastructure to avoid damages from flooding is very costly and it will take time before the necessary changes are implemented. Implementation of SURFF does not require much time and is in comparison cheap.

Flood Warning tool
The tool is based on weather prognosis and a terrain model combined with a model of the pipe flow. When the flood warning tool SURFF calculates that a forecasted rain gives rise to more than 10 cm of water on the terrain in a larger area a warning is issued. The aim is that the produced warnings are sufficiently accurate to predict flooding and at the same time avoid alerting police and emergency teams unnecessary. The tool was developed as a result of the OMOVAST-project.

The data need
The necessary information which has to be available for the forecast of the flooded areas:

• Numerical Weather Prognosis provided from the local Meteorological Institute (e.g. measured rain from rain gauges in the area and forecasted rain for the next 6 hours).
• Measurements of seawater level.
• Model of the city (terrain as well as the pipe system).

Results of the flood warning tool
SURFF can provide the following prognosis based on the model calculations:

• Resulting water flows and water levels on the surface and in the pipes from the forecasted rain for the coming 6 hours. If the model calculates flooding for the forecasted rain, a warning will be sent to the person on duty.
• The flooding results for the forecasted rain are published on a web page. When the person on duty receives a sms from SURFF with a flood warning she/he will open the web page and look for location and extent of the calculated flooding. Based on this, a decision can be made whether to send an alert or not.

Test areas in Copenhagen
SURFF is set up to provide flood warnings for 3 areas in or near Copenhagen. The flood forecasts can be used by the emergency management teams as a decision tool when deciding whether police, emergency response units or the public shall be alerted. The result of the SURFF is a map showing any forecasted flooding (see figure). This map is updated every hour and published on a website which among others the Emergency management team has access to.

The project OMOVAST was funded by the Danish Government. Krüger, together with HOFOR (the utility Company of Greater Copenhagen), Nordvand, BIOFOS and DMI have been responsible for the project. The objective of the OMOVAST project is to provide urban flood warnings.