Transboundary river management is critical for international relations, sustainable energy development, and ecosystem management. Hydropower development, while meeting downstream water demand, is crucial for fostering cooperation among countries sharing water resources. However, addressing this challenge under the context of climate change poses significant complexities. This study investigates the cooperation regarding hydropower production and water releases under the potential impact of climate change. We project future streamflow by the calibrated HBV hydrological model in three transboundary rivers originating from Ethiopia: the Upper Blue Nile (UBN), Omo, and Tekeze rivers. Subsequently, we compute the hydropower potential (maximum hydropower energy within a specific period) by optimizing water release policies using the adapted ’Reservoir’ R package. The hydropower potential and water release are analyzed based on 11 scenarios of water releases ranging from favoring the upstream country (Scenario 1) to benefiting downstream countries (Scenario 11) for the three example dams on the studied transboundary rivers: the Grand Ethiopian Renaissance Dam (GERD), Omo-Gibe III, and Tekeze dams. Our focus lies in identifying the cooperation ranges that provide optimal hydropower in the upstream and water release to the downstream among the varying water release policies within this scenario spectrum. The findings indicate that within an appropriate range for the minimum monthly water release threshold, the hydropower potential for the three study sites only has a small decrease, while the water release to downstream, especially for the driest month, can be 1.14–2.45 times larger compared to no water release constraints. For GERD and Omo-Gibe III, maintaining the monthly water release threshold of 30%-50% of the monthly flow is assumed to define the cooperation range in the historical periods. However, for Tekeze, the cooperation range is from 20% to 40% of the monthly water release. Due to climate change, the cooperation range for GERD and Omo-Gibe III is projected to decrease to 20–30% in future periods, whereas no significant impact is expected for Tekeze. The study reveals that future energy production of the hydropower dams on the transboundary rivers are influenced by the monthly minimum water release threshold, underscoring the need for adaptive cooperative strategies for both upstream and downstream countries in the face of climate change.