We are faced with increasing water scarcity conditions and we anticipate a further intensification of the gap between water supply and demand in the coming years, resulting from a combination of climatic and anthropogenic factors. The European Water Resilience Strategy recently adopted by the European Commission foresees increased competition for freshwater supplies, which may also result in the exacerbation of regional conflicts between upstream and downstream stake-holders, including those with riparian non-EU partners. This requires additional efforts to foster the sustainable management of shared water resources, considering the novel challenges posed by changing climate and changing water uses.
The first step in mitigating the water scarcity risk is to reduce demand across all sectors of the economy through measures that increase water savings, efficiency, and reuse. But along with demand reduction, additional water resilience may be gained by increasing the amount of water we store and by optimising its management. In addition to increasing water retention on land, we may need to plan new reservoirs, small or large, and we certainly need to revise or rethink the operation of the existing ones, when they do not adequately meet all the recent societal needs and constraints – considering all relevant actors – and when the current management rules do not pay adequate attention to the protection of aquatic and terrestrial ecosystems.
Reservoirs use has undergone significant changes over the decades. In the past, they were originally often built by a single user for a single, specific purpose. Today, the same reservoir, to be truly sustainable from an economic, social, and environmental point of view, should be designed or, when already existing, managed as a multi-purpose and multi-user asset. Modern reservoirs are tasked with meeting not just one but a variety of purposes: drinking water supply, irrigation, industrial uses, hydroelectric power production, flood safety, transportation, and recreational uses. Some of such purposes were sometimes not even contemplated when many of the existing European reservoirs were designed, often decades ago, such as planning the releases for environmental protection and for the support of ecosystem services.
Recently, renewed interest has arisen for reservoirs management in relation to the water-energy nexus. At a time when all countries are making efforts to increase the share of renewable sources in their energy mix, the role of hydropower is more crucial than ever. Reservoir-based hydropower is particularly important because it is the only renewable source capable of storing energy, allowing it to play an essential balancing role in fully exploiting variable renewable sources, such as solar photovoltaics and wind power, whose output is intermittent and independent of consumer demand.
Coupling solar photovoltaics with reservoir-based hydropower is especially effective due to the positive seasonal complementarity of energy production and its synergy with existing power transmission infrastructure. In particular, floating solar photovoltaics is recently gaining attention as a novel technology for enhancing solar-hydro hybridisation. In such plants, photovoltaic panels are installed on a floating structure, which is anchored to the bottom and/or the sides of the water body. With respect to traditional ground-mounted photovoltaic plants, this allows to preserve forested or cultivated land, to increase the PV panels efficiency thanks to the water-cooling effect and to reduce evaporation losses. Unfortunately, most countries still lack dedicated regulations for floating photovoltaic systems, which present both technological and legal barriers that need to be addressed to facilitate their evolution toward large-scale adoption. The European Commission Joint Research Centre (JRC) has estimated the potential of installing FPV on existing hydropower reservoirs across EU countries, showing that such coupling would allow to produce significant additional energy. In the Baltic region, such potential is particularly high in Finland and Sweden, thanks to the large surface area of the reservoirs. On the other hand, it should be highlighted that in this region, the cold climate and ice formation present additional engineering challenges.
Another novel technological challenge that is potentially very interesting to address the water-energy nexus, is the integration between pumped-storage hydropower plants, intermittent renewable sources and desalination plants. The integration between these systems allows to exploit excess wind or solar energy, which would otherwise be lost or limited by grid congestion, using it either to store hydroelectric energy in the upper reservoir or to power the desalination process that is highly energy-intensive. In this way, it is possible to simultaneously harness energy and water resources, improving the flexibility of the electricity system based on clean and renewable energy, while also contributing to water security through the production of drinking water.
Many European reservoirs were built decades ago and designed years before their construction. Significant transformations are expected or already underway in the use of our reservoirs, due to changes in both societal and environmental needs (including the water-energy nexus) and in the forcing predicted by future climate simulations. It is necessary to anticipate the impact of these changes, in a fully multi-purpose and multi-user framework, adapting the reservoir management rules and optimising them according to the different possible future scenarios.
Elena Toth
Professor
Department of Civil, Chemical, Environmental and Materials Engineering
University of Bologna
Italy
President
Italian Hydrological Society (SII-IHS)
Italy
