Comment on hess-2021-518 Anonymous Referee # 2 Referee comment on " Unfolding the relationship between seasonal forecast skill and value in hydropower production : A global analysis

The paper contributes a global analysis about the value of long-term forecast for hydropower reservoirs. Specifically, the authors contrast the performance of three alternative operating schemes, basic control rules, perfect forecast-informed, and realistic forecast-informed. The latter use forecast information generated with a statistical prediction model based on four large-scale climate drivers along with local drivers (inflow and soil moisture). Results obtained for 735 hydropower reservoirs show that most dams could benefit from perfect forecasts, with these gains that strongly depend on dam characteristics; only a small number of dams however attains a performance improvement when realistic forecasts are used. The topic of the paper is absolutely timely and important, and fits nicely within HESS scope. The numerical analysis is robust and well designed, and the manuscript is clearly written. Overall, I think the paper could be a strong contribution to the ongoing debate about the relationship between forecast skill and value. Below I'm suggesting a few points to further improve the paper before accepting it for publication.