Hydro-CH2018 Multi-purpose Reservoirs

Challenges for the multi-purpose use of reservoirs from the perspective of governance, ecology, landscape protection and economics

Due to climate change, snow cover and glacier mass will decrease, precipitation will shift more to the winter season, and more frequent summer droughts are to be expected. At the same time, the demand for water, especially for agriculture, is expected to increase in the summer months. In this context, the question arises how high the potential of water reservoirs is to reduce summer water shortages. In a first sub-project, the current and future summer water scarcity was estimated for 307 medium-sized catchments in Switzerland, and compared with the usable storage volume of natural lakes and artificial reservoirs. From a water balance perspective, the local potential of existing reservoirs to reduce water scarcity was found to be rather low. However, at the regional level (i.e. for larger catchments), it was shown that there indeed is a potential capacity to reduce water scarcity (Brunner et al. 2019).

In the second part of the project, it was analysed, which challenges for the multi-purpose use of reservoirs from the perspective of governance, ecology, landscape protection and economics exist, and how they can be solved. The following challenges are found to be of particular importance for water uses of reservoirs in Switzerland:

1. lack of data on hydrological and socio-economic impacts of multi-purpose use;
2. lack of awareness of (future) seasonal and regional water scarcities;
3. insufficient procedural and legal coordination of different uses;
4. lack of strategies to deal with water scarcity;
5. lack of adaptive capacity to climate change and socio-economic changes;
6. unresolved trade-offs (a) between conservation and use interests and (b) between mitigation (hydropower) and adaptation (irrigation, ecology) to climate change.

These challenges could be addressed with the following approaches:

1. raising awareness of water scarcity and developing data baselines;
2. implementing concrete recommendations for public policy and legislation; and
3. adhering to specific design criteria in participatory processes to develop options for multi-purpose use.

Research on ecological impacts has shown that changing the management of existing natural lakes and reservoirs towards increased multi-purpose use will result in minor additional impacts, only. This is particularly true when considered in relation to the existing ecological impacts caused by the current regulations of lakes and reservoirs. In specific cases, multi-purpose use could add ecological value, e.g., if hydropower reservoirs increase runoff in dry summers for downstream uses (Fig. 1). The literature search did not yield any significant new findings on the ecological impacts of new reservoir construction (Thür et al. 2020). In future, the local impacts will have to be analysed for each individual case within the framework of an environmental impact assessment

The analyses of the economic impacts of multi-purpose use have shown that a general cost-benefit analysis for the multi-purpose use of Swiss reservoirs is not expedient, because costs and benefits often occur regionally in very different places, often not where decisions are made. In the same vein, they are to the benefit/expense of different sectors or the general public. Nevertheless, there is evidence that increased multi-purpose use can have a positive net economic effect.

In summary, the results show that multi-purpose use of storage as well as multi-purpose storage cascades are a promising solution to mitigate summer water scarcity. However, this requires actively (1) addressing challenges related to water scarcity awareness and data, (2) implementing recommendations for public policy and legislation, and (3) developing and implementing principles for conducting participatory processes in order to ensure a continued water supply in Switzerland with the usual quality and reliability for different water uses.

The report concludes with recommendations for action for implementation at cantonal and federal level and the identification of further research needs (Kellner et al. 2021, PDF).

More about the 1st part of the project (2017-2019): Link