GHG emissions from hydroelectric reservoirs in tropical and equatorial regions: Review of 20 years of CH4 emission measurements

Greenhouse gas (GHG) emissions from reservoirs have been under the microscope for more a decade now. In particular, the high CH4 emissions reported in warm systems have tarnished the green credentials of hydroelectricity in terms of GHG emissions. Reliable estimates of CH4 emissions are crucial, since CH4 has a greenhouse warming potential of 25 and because, unlike CO2, CH4 emissions should be counted for the entire life cycle of a reservoir. Up to now, the highest CH4 emissions from reservoirs have been measured in warm latitudes, thus adding an argument against the use of hydroelectricity in these regions. However, to our knowledge, GHG emissions have been measured for only 18 of the 741 large dams (>10 MW, according to the ICOLD register) listed in the tropics. This article reviews the limited scientific information available and concludes that, at this time, no global position can be taken regarding the importance and extent of GHG emissions in warm latitudes.

► On the 741 large dams in the tropics (ICOLD), GHG emission measurements have been made on 18.
► Standard methodologies have only recently been proposed; past studies are difficult to compare.
► Available data (except Petit Saut) have a high level of uncertainty and may not be representative.
► Reservoir gross emissions are rarely higher than those from their thermal power plant equivalent.
► No global position can be taken regarding the importance of GHG emissions in warm latitudes.