Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
• A carbon source is an area that releases more carbon into the atmosphere than it absorbs.
Sources and sinks of carbon dioxide are crucial to maintaining the carbon cycle of the global environment.
Consequently, a reservoirs overall contribution to global climate change could increase or decrease
depending on the type of ecosystem flooded.
Gross emission from Gibe III Hydropower plant
The GIBE III project shows the main following characteristics:
• Surface: 20,599 ha
• Volume: 15,245 Mm 3
• Water resident time: 6 months
• Energy produced annually: 6,400 GWh
• Flooded area per unit of energy produced annually: 3,22 ha
The evaluations are leads following the GOOD PRACTICE GUIDANCE FOR LAND USE, LAND-USE
CHANGE AND FORESTRY (LULUCF) from Intergovernmental Panel on Climate Change (IPCC). The
Tier 1 is adopted.
The Tier 1 approach provides a simplified approach to estimating greenhouse gas emissions from reservoirs
using default emission data and highly aggregated area data. Unless otherwise indicated the area used in Tier
1 calculations is the flooded total surface area, which includes any areas covered with water before the
flooding, because area data minus these previously flooded areas are generally not available.
It is important to consider that the gross emissions overestimate the responsibility of the hydro reservoirs
CO2 emissions
The method to estimate the carbon stock change in aboveground living biomass due to land conversion to
flooded land assumes that all aboveground biomass is converted into CO2 in the first year following the
conversion. In actuality, the part of the above-ground biomass that is left on site before flooding will
decompose more slowly. Decay of soil carbon will also contribute to the emissions and a Tier 1 method for
these CO2 emissions is
CO2 emissionsWW flood = P ● E(CO2)diff ● Aflood, total surface
Where:
• CO2 emissionsWW flood = total CO2 emissions from flooded lands, Gg CO2 yr-1
• P = period, days (usually 365 for annual inventory estimates)
• E(CO2)diff = averaged daily diffusive emissions, Gg CO2 ha-1 day-1
• Aflood, total surface = total flooded surface area, including flooded land, flooded lake and flooded river
surface area, ha
The CO2 estimation method is simple – the only emission pathway that is estimated under Tier 1 is diffusion
emission during ice-free and ice-cover periods. CO2 bubble emissions are not significant. The default
CESI SpA - Mid-Day International Consulting Engineers Page 193