How rainfall models contribute to climate adaptation strategies

Related theme: Developing & Conserving a Resilient Living Environment 

Challenge

Mitigating flood risk
The German city of Boizenburg lies in the Elbe valley, on the banks of the Boize, a distributary of the Elbe river. This beautiful city and the surrounding area are at risk of flooding by heavier precipitation brought on by climate change. These extremes in weather mean that there will be more rainfall and longer periods of drought. Heavy rainfall on parched ground unable to absorb the excess water poses a further risk of flooding and waterlogging.  

These were all reasons for the City of Boizenburg to identify the future risk and plan mitigating and preventative measures. They wanted a predictive plan on which to base future, long-term decisions. TAUW was asked to provide that plan.

Solution

Precipitation model to highlight problem areas
TAUW developed and defined a detailed precipitation model for two climate change-related scenarios. The first scenario was for heavy rain with initial high-water levels, factoring in a climate change addition. The second scenario showed the effects in drought conditions, with lower initial water levels and same amount of rainfall.

The project involved preliminary investigation and data collection using GIS (Geographic Information System) mapping. The data was used in Tygron modelling software to calculate and develop the scenarios.   

Collecting all the relevant data was a particular challenge of this project. The data required is not standardised or stored centrally. To build a realistic model required enormous amounts of different data, ranging from a digital elevation model, information on water bodies in the area, land use and specifics of built-up areas, existing weirs, pumps and corresponding hydraulic parameters. The output was visualised in a video and detailed maps.

 Dry Scenario: with lower initial water levels and in parts reduced infiltration capacity of the soil

Impact

Solid plan on which to base climate adaptive measures
The maps showed vulnerabilities and problem areas. The scenarios we developed provide important information for the city of Boizenburg. The maps help to make clear what the consequences of heavy precipitation are and support practical preventative actions.  

The information is crucial for the emergency services and Federal Agency for Technical relief on which to base their response. Knowing that the hospital is located in an area at risk of greater water accumulation, allows emergency services to define alternative routes and ensure continued access to key urban facilities.  

The maps also help the local government in future planning decisions. For example, the scenarios show excess water collecting on the sports fields. These can serve as overflow and would therefore not be a suitable site for construction. The maps also showed which low-lying residential areas are at greater risk (marked in yellow on the maps). That information can help residents plan preventative measures.

The differences between scenarios showed that drought conditions caused additional problems with more water aggregating in agricultural area to the north. This project enhanced TAUW’s expertise in climate adaptive solutions.

Partnership 

The client is pleased with the scenarios. The maps are a solid basis on which to plan and develop future long-term mitigating measures, keeping the city and its surroundings safe. 

Julia Gerdsen, climate change coordinator with the  City of Boizenburg: “The heavy rainfall modeling has proven to be very helpful for us in general: On the one hand, we were able to use its results to create or strengthen awareness among citizens, politicians, and administrators about the consequences of climate change and the risks of heavy rainfall events. On the other hand, we were and still are able to emphasize and support the need for preventive measures such as rainwater management and desalination measures regularly based on the data and insights obtained. ”