Substantial greenhouse gas (GHG) emissions from hydropower reservoirs have been increasingly concerned recently, yet the significant carbon emitters of drawdown area and reservoir downstream (including spillways and turbines as well as river reaches below dams) have not been included in global carbon budget.  

Under the supervision of Prof. ZHANG Quanfa from Wuhan Botanical Garden, Dr. LI Siyue revisited GHG emissions from hydropower reservoirs by considering reservoir surface area, drawdown zone and reservoir downstream.

Their estimates demonstrated around 301.3 Tg carbon dioxide (CO₂)/year and 18.7 Tg methane (CH₄)/year from global hydroelectric reservoirs, which were much higher than recent observations. The sum of drawdown and downstream emission, which was generally overlooked, represented 42 % CO₂ and 67 % CH₄ of the total emissions from hydropower reservoirs. Accordingly, the global average emissions from hydropower were estimated to be 92 g CO₂/kWh and 5.7 g CH₄/kWh. Nonetheless, global hydroelectricity could currently reduce approximate 2,351 Tg CO₂eq/year with respect to fuel fossil plant alternative.  

The new findings show a substantial revision of carbon emission from the global hydropower reservoirs. Their study provides an important advancement on systematic quantification of hydropower-induced GHG emission and much needed data from Asia are included. 

The research was funded by the National Natural Science Foundation of China and Youth Innovation Promotion Association, the Chinese Academy of Sciences, China. Results were published in Environment Science and Pollution Research (DOI 10.1007/s11356-014-3165-4) entitled “Carbon emission from global hydroelectric reservoirs revisited”.