The Wupper catchment area lies in the state of North-Rhine Westphalia, Germany, with an area of 813 km² and a river network of approx. 2.300 km. The Große Dhünn reservoir (GDT) is located within the Dhünn catchment area, the main tributary of the Wupper. The Wupper then meets the Rhine at the city of Leverkusen. The Mirke Creek in Wuppertal is a typical brook in that area for flush floods.
The topography varies between 40 and 500 MASL, with mean annual precipitation (MAP) ranging from 750 to 1.450.
Which sectors did it involve?
Most relevant stakeholders include federal authorities, district governments, municipalities, environmental agencies, drinking water suppliers, power generating plants, trade and industrial organizations, and insurances. Stakeholders were engaged to contribute perceptions and understanding about climate change. Case studies too much water (flash floods at Mirke Creek) and not enough water (water availability stress at GDT) were defined together as well as adaptation measures and structural gaps.
What was done?
A set of (hydrological) impact models were set-up, calibrated, and validated to investigate the local effects of climate change in combination with land and water use scenarios. The models were driven with meteorological input data based on decadal predictions, and climate projections.
Past extreme dry periods were evaluated based on long-term precipitation time series, indicated by indices like SPI and SPEI and correlated to storage volume of the reservoir. The simulated future scenarios were sorted in the same way to determine possible developments. For flush floods extremal episodes with heavy rainfall events were simulated based on high-resolution downscaling.
A network of soil moisture sensors and tensiometers were installed in the catchment upstream of GDT accompanied by field tests and laboratory analysis. The monitoring of soil moisture and tension rose from the need to achieve a better knowledge of the flow processes and to improve the hydrological models based on measurements.
Which were the main results?
Temperature and evapotranspiration rates are expected to increase, mainly in summer, with a meaningful impact on rainfall regimes. The inflow to GDT reservoir is likely to increase in fall and decrease in spring. In the GDT catchment land use changes are minor due to protection zones, but reservoir volume proved to be highly sensitive to the different water use scenarios. Less small events and more extraordinary events are expected related to flush floods which have a high impact on damage costs.
What is BINGO’s legacy in Wupper?
To highlight is the improvement of understanding and knowledge in usage and interpretation of climate data based on regional models in close interaction with the meteorologists: The leads to a better communication of possible future development and supports decision making processes for adaptive behaviour. To capture accurately extreme convective heavy rainfall, high temporal and spatial resolution are fundamental. Technical results are also improved models and knowledge on soil processes including technical infrastructure and processes to manage and analyse large amount of data sets. In addition, the determination of representative indices demonstrated to be a robust method for comparison between several data sets and uncertainties.
A concept of prioritisation of effective adaptation measures was developed including also non-monetary weighting. For flood risk reduction not only structural measures were analysed and proposed also property protection is identified with meaning potential.