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Greenhouse gas emissions

Hydropower is a low-carbon technology which helps to mitigate the carbon emissions of fossil fuels.

Hydropower generates more than 4,000 terawatt hours of electricity globally every year, enough to supply over 1 billion people with clean energy.

If hydropower was replaced with burning coal, more than 4 billion metric tonnes of additional greenhouse gases would be emitted annually, and global emissions from fossil fuels and industry would be at least 10 per cent higher.

Carbon footprint of reservoirs

In certain conditions, a reservoir created by a hydropower dam will release greenhouse gases due to the decomposition of flooded organic materialIn other conditionsa reservoir may act as carbon sink: absorbing more emissions than it emits.

A number of researchers have measured reservoir emissions at dam sites around the world, but each study is usually site-specific and the results not applicable to the great majority of reservoirs elsewhere.

Since 2006, IHA has been working with UNESCO, the World Bank and range of stakeholders to develop common understanding to assess the carbon profile of hydropower facilities and reservoirs

This work resulted in the publication of the UNESCO/IHA GHG Measurement Guidelines for Freshwater Reservoirs.

G-res Tool

In 2017, in collaboration with the UNESCO Chair for Global Environmental Change, IHA launched a publicly available online tool that allows hydropower companies, investors, consultants, decision-makers and other stakeholders to more accurately report on the net impact on greenhouse gas (GHG) emissions

The G-res tool uses a new modelling methodology based on current scientific knowledge and over 500 empirical measurements from more than 200 reservoirs worldwide.

Using readily available input data, it provides a way to assess GHG impacts without the need for large-scale field measurement campaigns and multi-year studies.

The G-res tool builds upon a new conceptual framework developed in cooperation with researchers from the University of Quebec at Montreal (UQÀM), the Norwegian Foundation for Scientific and Industrial Research (SINTEF) and the Natural Resources Institute of Finland (LUKE). Find out more.

Study data

In the 2018 Hydropower Status Report, IHA highlighted the findings of its study of 178 single purpose hydropower reservoirs and 320 multipurpose reservoirs using the G-res Tool.

The global median GHG emission intensity of the hydropower reservoirs included in the study was 18.5 gCO2-eq/kWh - this is the grams of carbon dioxide equivalent per kilowatt-hour of electricity generated allocated to hydropower over a life-cycle. Read more.