Results of the Meuse extreme drought Hackathon : a report on the observations shared by the participants

On 11 September 2024, a Meuse extreme drought hackathon was hosted at the University of Liège, aimed to: 1) Better understand the different interests and impacts of droughts among the Meuse River Basin countries. This enables the integration of hydrological system knowledge and promotes informed decision-making both during and after droughts in a transboundary context. 2) Create awareness about the importance of international cooperation in the field of water allocation by enabling a water dialogue. To reach these aims, 24 hydrological experts from Germany, France, the Netherlands, Flanders, and Wallonia were invited to participate in the hackathon. We collaboratively answered the following research question: What is the impact of an extreme drought on the Meuse River Basin and consequently different sectors and regions? What can be done to reduce this impact and/or create synergies? Multiple impacts of the extreme drought were identified by the participants and clustered per sector. For example: • For industry and energy, power plants will likely be shut down, resulting in less heating of the Meuse, as well as reduced hydropeaking. • Not all Meuse countries are equally dependent on the Meuse for drinking water: The Netherlands and Wallonia can more easily switch to other sources, whilst Flanders depends highly on the Meuse for drinking water. Salt intrusion might require the drinking water intake points to move further inland. • Nature at the Grensmaas is vulnerable and will likely be impacted to a large extent. For nature in general, a minimum flow is necessary. • Irrigation is one of the first uses restricted in their water use during droughts, resulting in economic damages and likely more import of agricultural products. • Shipping becomes less reliable during droughts and has the highest priority for water allocation in Wallonia. • There is still a lack of coordination in water prioritization, possibly resulting in unequal and inefficient distributions. To reduce the identified impacts, short-term and long-term measures and synergies were discussed, including combinations of both structural and non-structural solutions, as well as combinations of nature-based and grey solutions. Multiple measures were brought forward by the participants on four topics, for example: 1) Water demand reduction: Increased awareness and more recycling and reuse. 2) Sectoral and spatial adaptation: Implement diversification of sources for drinking water and implement closed-loop cooling for energy and industry. 3) Conflict prevention: Enable knowledge exchange platforms and cooperation between drinking water companies. 4) Water retention and nature-based solutions: Bring back the sponge function of the landscape and increase the number of reservoirs. A discussion on next steps with the participants resulted in the following recommendations: • Quantify the goals we want to achieve within the hydrological system, (e.g. to achieve a certain sponge function) and quantify the impact of identified measures; • Improve knowledge on governance structures and discuss the implementation requirements for different measures (e.g. necessary Meuse agreements).