When Timing Matters - Misdesigned Dam Filling Impacts Hydropower Sustainability

In 2020, global hydropower installed capacity reached 1,330 GW and more than 3500 hydropower dams are currently being planned or built around the world. Recently, efforts towards sustainable dam planning have addressed strategic dam sizing, dam location, and basin-wide portfolios to minimize long-term impacts of such infrastructures. Yet, before starting electricity production, hydropower reservoirs must be filled withholding a substantial fraction of the river streamflow from downstream users. The rate at which a reservoir is filled has direct implications on potential conflicts between upstream and downstream interests: precaution towards downstream impacts requires transiting high percentages of inflow, resulting in multi-years, even decadal, filling transients; conversely, upstream interests (e. g., hydropower production) favor fast impoundment of water, albeit generating critical periods of minimal streamflow downstream. Filling timing and operations can therefore catalyze most of the conflicts associated with a dam’s lifetime, which can be mitigated by adaptive solutions that respond to medium-to-long term hydroclimatic fluctuations. If the filling occurs during a dry spell, augmented impacts are likely endured by upstream and downstream sectors. In this context, global climate teleconnections represent a valuable source of predictability of local hydrometeorological anomalies, which can provide dual support to dam planning. First, in scheduling a favorable time to start the filling operations based on local effects of long-term climatic oscillations, and second, in designing effective filling strategies adaptive to medium-term hydroclimatic variability. In this work [1], we consider the case study of the Omo-Turkana basin (Ethiopia-Kenya) to demonstrate the use of seasonal drought forecasts based on multiple climate teleconnections for modulating reservoir filling operations according to the predicted drought conditions. Our retrospective analysis of the contested recent filling of Gibe III provides quantitative evidence of the benefits generated by adaptive filling strategies, attaining levels of hydropower production comparable with the historical ones while curtailing the negative impacts to downstream users. Our approach also shows that 2015 was an unfavorable year to begin the filling operations of Gibe III, and significant damage could be avoided by anticipating these operations by 2 years (see Figure 1). Our results can inform a more sustainable filling of the Koysha dam currently under construction downstream of Gibe III or the upcoming filling of the Grand Ethiopian Renaissance Dam on the Blue Nile, and are generalizable to the almost 500 planned dams worldwide in regions influenced by climate feedbacks, thus representing a significant scope to reduce the societal and environmental impacts of a large number of new hydropower projects