7 things you should know about GHG emissions related to hydropower & reservoirs
Hydropower has been a reliable and a critical tool in the fight against climate change, and in achieving national and international objectives towards reducing greenhouse gas (GHG) emissions. This is particularly true in the developing world where untapped sources of hydropower remain important[1]. Yet, the use of this energy is not without controversy, especially when it comes to GHGs. What is the current state of hydropower and what are the benefits? How does it contribute to sustainable development? Where are hydropower-related emissions coming from and how can they be calculated and monetised?
While hydropower newly installed capacities have been increasing since 2001, they are not on track for longer term sustainable targets. Hydropower can be considered a low-carbon source of energy but hydroelectrical plants with large reservoirs relative to their generating capacity can emit at least as much GHG emissions as fossil fuel plants[2]. These emissions mostly stem from reservoirs as well as construction and decommissioning. Despite the uncertainty to account for these, the use of the G-Res tool can help assess these. Under certain conditions hydropower projects are eligible for carbon finance.
Hydropower is still growing
Hydropower is the first source of renewable electricity. Its contribution to global renewable electricity production has been rising steadily since 2001. The International Hydropower Association (IHA) reported that, worldwide, more than 21.8 gigawatts (GW) of renewable hydroelectric capacity was put into operation in 2018. This is equivalent to the total electrical capacity of Chile or Belgium[3].
In 2018, China added the most capacity with 8,540 megawatts (MW), followed by Brazil (3,866 MW), Pakistan (2,487 MW), Turkey (1,085 MW), Angola (668 MW), Tajikistan (605 MW), Ecuador (556 MW), India (535 MW), Norway (419 MW) and Canada (401 MW). The allocation by country and region is presented in the figure below.
Hydropower installed capacity worldwide in 2018[4]
According to the International Energy Agency (IEA), over the next five years, hydropower capacity should increase by 9%, led by China, India and Brazil.
To illustrate the disparity of potential and implementation, the Democratic Republic of Congo which has 35% of the whole African continent potential (i.e. 100 GW) only has 2.6 GW installed, not even enough to merit a position on the above chart.
The unlimited benefits of hydro
All in all, countries, in particular those of the developing world, expect hydropower to make a significant contribution to the United Nations Sustainable Development Goals[5], in particular by enabling them to limit, or even reduce their levels of GHG emissions stemming from electricity generation activities. Hydropower is thus expected to help deliver affordable and clean energy, manage freshwater, combat climate change and improve livelihoods.
Power-related benefits include clean and flexible generation and storage, as well as reduced dependence on fossil fuels and avoidance of pollutants. In terms of livelihood, benefits also include economic and local supply chain improvements, enhanced navigation and transportation, and investment in community services. Freshwater management benefits include supply for homes, industry and agriculture, and mitigation against floods and drought[6].
Hydropower could provide for a broad range of benefits, and not only on-demand clean electricity.
Hydropower is needed for sustainable development
Needless to say, hydropower could play its part in reaching the objective of limiting climate change to 1.5°C or 2°C. In terms of adaptation, hydropower projects may offer countries protection against the impacts of climate change and extreme weather (e.g. floods or drought), even though variable climate conditions also make these projects susceptible to climate risks due to their dependency on precipitation and runoff.
According to the IEA, a continuous growth in new-build capacity is required to maintain an average generation increase of 2.5% per year through 2030 to remain on track with the Sustainable Development Scenario (SDS)[7]. As shown in the figure below, although growth prospects for new hydropower capacity remain strong, they are not sufficient to reach the SDS[8] level.
Hydropower generation in the Sustainable Development Scenario, 2000-2030
Yet, hydropower still contributes heavily to global emissions reduction efforts. As of March 2020, hydropower projects represented a staggering 24% of all carbon projects certified under the UNFCCC Clean Development Mechanism (CDM). It was as such, the most important category of project under the CDM[9].
The problem of hydropower GHG emissions
Hydropower is generally considered as a low-carbon technology and can act as a balance to the carbon- and pollutant-intensive fossil fuels. If hydropower was replaced with burning coal, up to 4 billion tonnes of additional GHG emissions would be emitted per year and global emissions from fossil fuels and industry would be at least 10% higher[10]. According to the Intergovernmental Panel on Climate Change (IPCC) and IHA, the median lifecycle carbon equivalent intensity of hydropower stands at 18.5 gCO2e per kWh, and only onshore wind would do better as can be seen in the figure below.
Carbon intensity of hydropower vs other technologies
When looking at the variation of emissions for each technology, we realise that hydropower is the technology that features the greatest range of emissions. It could either be the least, or the most, carbon-intensive technology[11].
Carbon footprint variation of energy sources
Run-of-river hydropower installations primarily use the natural flow rate of water to generate power, as opposed to the power of water falling with large dams with reservoirs. They tend to have very low levels of GHG emissions and have limited environmental and social impacts on local ecosystems and communities.
Reservoirs are the source of its problem
We have determined that the following parameters have a critical effect on the final emission level (ranked from most to least impacting):
Average temperature (more generally local climate and variations, including precipitation and wind velocity impacting to a lesser extent)
Size of reservoir versus the installed capacity (more generally the dam’s physical characteristics)
Services assigned to the reservoir (which would act on the allocation of emissions to activities other than electricity generation)
Cumulated mean horizontal solar radiance
Reservoir volume (as a function of depth and surface)
Land use patterns (including population levels) in catchment area/reservoir area pre- and post- impoundment as well as size of catchment area
Other factors such as soil carbon content (in the reservoir) and other biophysical characteristics of the catchment area, including fauna and flora characteristics and canopy cover
Interactions between these parameters are often complex and involve non-linear responses. Emissions stemming from these interactions are as such difficult to predict and estimate with precision.
Depending on the decommissioning method used, there may be secondary emissions from the carbon sink that are created when the reservoir is dried up.
Emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are part of the biogeochemical cycles of carbon and nitrogen from water bodies in natural environments. Hence, local emissions may be altered in areas affected by the development of reservoirs used for hydropower, flood control, drinking water, irrigation, navigation or other water uses[12].
GHG emissions from reservoirs generally stem from:
The decomposition of organic matter flooded by the reservoir and the biomass that grows and enters the reservoir as inflow during the life cycle. Emissions from flooded lands can occur through the following pathways after flooding: (1) molecular diffusion across the air-water interface (diffusive emissions); (2) CH4 bubbles from sediment (bubble emissions); (3) emissions resulting from the passage of water through a turbine and/or through the weir and downstream turbulence (degassing emissions); and (4) emissions from the decomposition of above-ground biomass
Construction, operation and dismantling activities.
Human activities in the catchment area or reservoir can also influence water quality and thus the eutrophication of water bodies and therefore create conditions for increased methane formation.
In tropical and subtropical areas, CH4 emissions are minimised in winter and maximised in summer and the decomposition of above-ground biomass (i.e. the biomass of trees not submerged during flooding) can be an important source of emissions.
The emissivity level is generally considered to be relatively high during the first few years after flooding, up to the first 10 to 20 years as can be seen in the figure below representing emissions from an Andean dam. Recent studies suggest that CO2 emissions during the first 10 years after flooding are the result of the decomposition of organic matter in the field prior to this event, while subsequent CO2 emissions come from material transferred to the flooded area[13].
Typical emissions pattern from reservoirs[14]
Finally, the issue of climate change must also be considered, as a feedback loop. An average increase in mean annual temperature in tropical and subtropical regions, as is predicted under both the 1.5°C and 2°C warming pathway for sub-Saharan Africa[15], could lead to increased emissions from reservoirs.
Calculation of GHG emissions
The IHA, along with the United Nations Educational, Scientific and Cultural Organization (UNESCO) developed a freely accessible GHG emissions calculation tool to quantify the portion of GHG emissions that can be attributed to the creation and operation of a hydroelectrical reservoir: the G-Res tool[16]. The use of this tool is recommended by the IEA, IAH, UNESCO and the World Bank to perform such a calculation.
However, since the G-Res tool is only as precise as the data entered into it, it is worth considering the IPCC-recommended three-tier approach in selecting data used to calculate emissions. Tier 1 is based on general estimation drawn from secondary data. Tier 2 is based on regional data, drawn from secondary bibliographical sources, while Tier 3 is drawn directly from primary data, collected in the field.
Using the G-Res tool is a relatively complex process. All the parameters described above are accounted for by the tool as inputs. Most need to be entered manually by the user. Some can be calculated using the tool’s database (the earth engine). For others, standardised values taken from the same database, can also be used.
As can be seen in the figure below, the tool offers a complete solution to calculate emissions from a dam/reservoir over a period of 100 years. Natural and man-made emissions from the catchment area, from the reservoir, as well as those produced in the construction phase are processed to give a full picture of a project’s GHG emissions, with a 95% confidence level.
Users are also given the possibility of comparing their results with those of equivalent dams/reservoirs. Values for emission factors are standardised but can be modified if necessary.
In order to get an accurate estimate, it is necessary to know with precision how to enter each parameter in the tool and field data.
Finally, the tool remains imprecise when it comes to calculating emissions for complex hydroelectrical installations, such as cascade dams.
G-res Tool web interface
Certifying emission reductions from hydropower
The cost of hydropower can be high but remains overall in the fossil fuel cost range or below as can be seen in the figure below. In many developing countries, the investment and institutional environment can make infrastructure projects unattractive to investors.
One way of facilitating and encouraging contributions from hydropower to global emission reductions objectives is by certifying and monetising the emission reductions to increase their investment profile, notably through a better return on investment and risk reduction.
Global levelised cost of electricity from utility-scale renewable power generation technologies
Certifying emission reductions stemming from hydroelectricity entails starting with finding the appropriate standard and emissions reduction methodology.
Because of uncertainties surrounding the emissions levels of hydropower, the CDM’s Executive Board excluded projects with a power density below 4 watts per m2 of reservoir surface (e.g. a very large reservoir in relation to the capacity installed) from being eligible to existing calculation methodologies. For similar reasons, projects with installed capacity that are over 15 MW (for the Verified Carbon Standard - VCS) and 20 MW (for the GS4GG) are not eligible to certification. The graph below shows the lower the power density, the higher the emission per unit of electricity produced, especially in tropical and sub-tropical areas.
Power density vs emission intensity[17]
Only those projects avoiding further emissions and requiring the financial revenues to be financially viable could benefit from international carbon finance.
How HAMERKOP can support
HAMERKOP Climate Impacts has worked with the European Union and other institutional clients in assessing emission levels and estimating emission reduction potential for several hydroelectrical installations in West Africa.
We hold the necessary expertise to help prospective developers assess, estimate and determine emissions from their future and present hydroelectric projects.
We can also evaluate the feasibility of certifying your project to carbon certification standards to allow them to benefit from their full economic value, by enabling selling of carbon credits on the voluntary or compliance carbon markets.
Under the Paris Agreement, the international cooperation mechanisms under article 6 could help you benefit from international climate finance and we can help you assess and set-up a strategy to achieve this.
SOURCES
[1] IHA (2019) Hydropower Status Report: https://www.hydropower.org/statusreport
[2] International Rivers (2019) Reservoir Emissions: https://www.internationalrivers.org/campaigns/reservoir-emissions
[3] CIA (2017) The World Factbook. Electricity, installed generating capacity is the total capacity of currently installed generators: https://www.cia.gov/library/publications/the-world-factbook/rankorder/2236rank.html
[4] IHA (2019) Hydropower Status Report: https://www.hydropower.org/statusreport
[5] IHA (2015). Sustainable Development Goals: how does hydropower fit in? https://www.hydropower.org/blog/sustainable-development-goals-how-does-hydropower-fit-in
[6] IHA (2019). Hydropower Status Report: Sector Trends and Insights: https://www.hydropower.org/sites/default/files/publications-docs/2019_hydropower_status_report_0.pdf
[7] IEA (2019) Tracking Power : https://www.iea.org/fuels-and-technologies/hydropower
[8] The IEA’s Sustainable Development Scenario (SDS) outlines a major transformation of the global energy system, showing how the world can change course to deliver on the three main energy-related SDGs simultaneously, by 2050 (SDG 7, SDG 3 & SDG 13). The SDS holds the temperature rise to below 1.8°C with a 66% probability without reliance on global net-negative CO2 emissions; this is equivalent to limiting the temperature rise to 1.65°C with a 50% probability. IEA (2019) SDS: https://www.iea.org/reports/world-energy-model/sustainable-development-scenario
[9] IGES (2020) IGES CDM Project Database: https://www.iges.or.jp/en/pub/iges-cdm-project-database/en
[10] IHA (2019) Hydropower Status Report: Sector Trends and Insights: https://www.hydropower.org/sites/default/files/publications-docs/2019_hydropower_status_report_0.pdf
[11] Sherer, L., Pfister, S., (2016). Hydropower's Biogenic Carbon Footprint. PLOS ONE., 11(9). P. 11: https://doi.org/10.1371/journal.pone.0161947.
[12] IEA (2018) Hydropower Annex XII: Guidelines for Quantitative Analysis of Net GHG Emissions from reservoirs – Volume 3: Management, Mitigation and Allocation.
[13] IPCC (2019). IPCC Good Practice Guidance for LULUCF 3.285; Chapter 3: LUCF Sector Good Practice Guidance
[14] Forsberg BR, Melack JM, Dunne T, Barthem RB, Goulding M, Paiva RCD, et al. (2017) The potential impact of new Andean dams on Amazon fluvial ecosystems. PLoS ONE 12(8): e0182254. https://doi.org/10.1371/journal.pone.0182254
[15] IPCC (2019). IPCC Good Practice Guidance for LULUCF 3.285; Chapter 3: LUCF Sector Good Practice Guidance
[16] UNESCO/IHA research project on the GHG status of freshwater reservoirs (2017). The GHG Reservoir Tool (G-res) Technical Documentation.
[17] IHA (2018). Study shows hydropower’s greenhouse gas footprint: https://www.hydropower.org/news/study-shows-hydropower’s-carbon-footprint