Nitrous oxide dominates greenhouse gas emissions from hydropower's reservoirs in China from 2020 to 2060

China is ambitious to increase its hydropower share to mitigate climate changes. The greenhouse gas (GHG) emissions from hydroelectric reservoirs may hinder the climate goal. The spatio-temporal patterns of such emissions under future climate changes at the national scale are not clearly addressed. In this study, we evaluate these emissions from 79 hydroelectric reservoirs across China (61.22 % of the national hydropower generation) in 2020, covering carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), using the G-res (Greenhouse Gas Reservoir) tool and Integrated Model to Assess the Global Environment-Dynamic Global Nutrient Model (IMAGE-DGNM). A random forest (RF) model is also used to project the emissions in the period of 2020 to 2060 under Shared Socioeconomic Pathway (SSP) scenarios. The results indicate that the carbon intensity (CI) and areal flux varied largely. The reservoirs located in low-altitude areas and older reservoirs generally have higher CIs. N₂O contributed with more than 80 % of the total GHG emission, in which the NH₄⁺ concentration is a key factor influencing the N₂O emissions. The projection shows that these emissions will increase by 1.30 %, 6.63 %, and 17.33 % in 2060 compared to 2020 under the SSP119, SSP245, and SSP585 scenarios, respectively, in which CH₄ has the largest growth. Finally, implications toward reduction in such emissions are discussed.