The overarching objective of the study was to gain insights in the future role of hydropower assets in a decarbonised energy system. For this purpose, it deemed appropriate to review the hydro dispatch strategy of flexible hydro assets in the EU energy system model METIS. Instead of relying on guidance curves based on historical data, the idea was to incorporate a forward-looking view, that would reflect the full flexibility offered by hydropower plants and allow modelling a more realistic dispatch of these units. This involved the integration of more reliable statistical data on annual hydro power generation and installed capacities. Further, it proved useful to represent the stochastic nature of hydro inflows for both run-of-river and reservoir assets. This was achieved by equipping METIS with variable inflow profiles (time series data) for 28 historical weather years, in line with the modelling of other renewable energy sources (solar PV & wind). Building further on these upgrades, it became possible to update the guidance curves of hydro reservoir assets, making use of Stochastic Dual Dynamic Programming (SDDP). A detailed explanation of the chosen approach is discussed in the report, which is completed by a set of illustrative results, including a sensitivity on the impact of climate change.