Modelling Water-Energy-Food-Ecosystems (WEFE) Nexus Trade-offs and Synergies in a meso-scale watershed in the European Alps

Despite being historically water-abundant, many mountain regions of the world are forced to adapt to a drier and hotter climate. Adaptation in the water sector calls for a revision of policies, the introduction of new regulations, and changing water allocation priorities, which in turn rely on a sound understanding of water supply-demand balance. In investigating water allocation issues, it is paramount to consider the interconnectedness of water-dependent sectors, i.e. water supply, energy, food, and ecosystems (the Water-Energy-Food-Ecosystems – WEFE - Nexus), so that trade-offs between sectoral objectives are minimised and synergies built. In this study, we assess the magnitude and seasonality of trade-offs and synergies between hydropower production, irrigation, and ecological flows for the Orco watershed, a mountainous sub-basin of the Po River in Northern Italy. A water resources management model is built using the Water Evaluation And Planning (WEAP) software tool and integrating simulation of hydrological processes with a priority-based, cross-sectoral allocation model. The model is used to perform an ex-post assessment of water management strategies adopted in the period 2011-2022, considering thus both wet and dry years conditions, including the extreme drought in summer 2022. Baseline conditions of water allocation across sectors are informed by a review of water policies and interviews with local stakeholders, while alternative management scenarios are built based on assigning different priorities to hydropower production and irrigation, and by increasing ecological flow requirements. The impact of alternative water management strategies on meeting sectoral water demands is thus simulated to reveal trade-offs across sectors (e.g., hydropower-irrigation, irrigation-ecological flows) and between agricultural upstream and downstream water users. Results show the Orco watershed faced recurrent water scarcity conditions in the simulated period with the most downstream irrigation consortium having experienced a supply deficit in most years. Trade-offs between hydropower and irrigation typically occur in late July and August when agricultural water demands exceed reservoirs’ outflow needed for hydropower production. If irrigation needs had been prioritised over hydropower production in the management of reservoirs, our study indicates that the supply deficits experienced by irrigation consortia would have been significantly lowered in the period 2011-2021, leading, however, to a moderate loss of hydropower production in autumn and winter. In 2022, the benefits gained from a different operation of reservoirs would have been significantly smaller due to the large supply deficit already manifested at the start of the irrigation season (April - May) and very low levels in reservoirs throughout the 2022 hydrological year. Finally, the upstream positioning of agricultural water users is shown to have a drastic impact on the frequency and magnitude of supply deficits faced by irrigation consortia and on the impact of stricter ecological flow requirements on agricultural water withdrawals. Through the modelling of WEFE Nexus trade-offs and synergies we provide evidence that can help public authorities and water users further assess the impact of regulatory and infrastructural developments in mountainous watersheds.