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Hydropower is the largest source of renewable electricity and a central component of the water–energy nexus and the net-zero transition. Aging infrastructure, combined with climate variability and evolving grid demands, is reducing the efficiency and operational flexibility of Hydropower Plants (HP) designed for past climate and grid conditions. Meeting future energy needs requires modernizing the existing fleet, for example through turbine replacement which occurs every few decades.In practice, turbines are often replaced with identical units that replicate legacy configurations optimized for past conditions, but replacements constitute an opportunity to redesign turbine head and discharge capacity to match evolving hydrology, reservoir operations, and grid needs. In drought-prone systems, for example, installing units optimized for lower head can sustain generation at reduced reservoir levels, as demonstrated by recent upgrades at Hoover Dam on the Colorado River. What is missing is a rigorous method to determine when and how turbines should be upgraded to ensure efficient, reliable, and sustainable outcomes.This study addresses this need for large-scale hydropower upgrades by using a newly developed framework, HyTUNE (Hydropower Turbine Upgrade and Next-generation Planning). HyTUNE is a dynamic decision-support tool that integrates basin hydrology, HP hydraulics, and adaptive optimization to inform turbine replacement timing and configuration. HyTUNE learns from evolving system states and identifies threshold conditions where adjustments to design head or discharge capacity improve hydropower performance.Application to the Hoover Hydropower Plant in the Colorado River Basin shows that HyTUNE’s adaptive policies consistently outperform benchmark replacement strategies across diverse hydrologic futures. The approach increases economic returns, measured as net present value, and enhances plant capability through higher firm power, peak-period generation, and operational efficiency, with fewer turbine replacements. Climate variability still shapes outcomes, with the largest benefits of HyTUNE compared to benchmark expected under wetter conditions, and the strongest improvements in firm power and operational efficiency under drier conditions. HyTUNE offers a practical framework for hydropower systems facing the combined challenges of modernization, climate uncertainty, and growing demand.