Assessing Carbon Emissions from Reservoirs in China: Insights from the G-res Model and Implications for Hydropower Planning

Reservoirs are an important source of emissions of carbon-based greenhouse gases (GHGs). China has about tens of thousands of reservoirs, about half of the world's total reservoirs, and therefore needs a more accurate estimate of current carbon emissions from reservoirs. This study utilizes the Greenhouse Gas from Reservoirs (G-res) model to assess CO2 and CH4 fluxes for 1479 reservoirs in China. The findings reveal that Chinese reservoirs contribute 0.156 Tg CO2 eq yr−1 in CO2 emissions and 6.657 Tg CO2 eq yr−1 in CH4 emissions. Across the nine main river basins in China, negative CO2 diffusive emissions from reservoirs are observed where large size reservoirs were attributed specifically the Northern inland and Xinjiang basin, southwest international basin, Yangtze basin, and Pearl basin. Similarly, CH4 fluxes through degassing and ebullition diffusion pathways exhibit a decreasing trend from small to large in the categorisation according to storage capacity. The findings in this study investigated significant GHG emissions from reservoirs in China, but also highlighted the different circumstances under which certain large reservoirs have the potential to act as CO2 carbon sinks. In order to reduce greenhouse gas emissions, it is crucial to strategically review hydropower planning, in which the cumulative effects of small reservoirs and the large impacts of large reservoirs should be considered.