Carbon footprints of two large hydro-projects in China: Life-cycle assessment according to ISO/TS 14067

Hydropower offers significant potential for reductions in carbon emissions. Nevertheless, the past two decades witnessed growing worldwide concerns about excessive greenhouse gas (GHG) emissions by damming and reservoir creation. Carbon footprint of a hydro-project within its full life-cycle is scientifically reasonable to evaluate the climate impact of hydropower. Located in the upper course of the Yangtze River, the Xiluodu (XLD) and Xiangjiaba (XJB) dams are the second and third largest hydro-projects in China. Following ISO/TS 14067, system boundary of the life-cycle assessments included pre-impoundment clearance, construction, reservoir operation, maintenance and dam decommission. GHG emissions from different land cover in flooded area are specially considered to estimate reservoir net GHG emissions. The life-cycle GHG emissions of the XLD and XJB hydro-projects are 7.60 ± 1.09 gCO2eq/kWh and 9.12 ± 1.36 gCO2eq/kWh, respectively. Reservoir CH4 and CO2 emissions and the potential release of CH4 from sediment in phase of dam decommission are the most sensitive factors. Through direct allocation of life-cycle GHG emissions according to water consumption, 95.9% and 97.2% of the emissions in XLD and XJB are allocated to hydropower. In comparison with global cases, energy payback and life-cycle GHG emissions of both hydro-projects were competitive, supporting excellent environmental and energy performances.