Estimation of CO2 emissions in the life cycle of roads through the disruption and restoration of environmental systems

• A method for estimating the CO2 budgets from land-use changes in road projects.
• We estimate C stocks related to land-use categories of Spanish environmental systems.
• Destruction of environmental systems releases 550 to 3660 t CO2e km−1 in case studies.
• Long term C sequestration by optimal restoration may largely offset such emissions.
• A required analysis in order to integrally assess the GHG emissions in road projects.

Effects of disruption and restoration of terrestrial ecosystems have been largely overlooked when conducting assessments of greenhouse gas (GHG) emissions in road construction projects. This is an important oversight given the intensive land-conversion generated by linear infrastructure development, as well as the relevance given to carbon pool variations associated with land use and land-use changes by national inventories of GHG emissions and global reports. This paper describes the implementation of a methodology to classify those environmental systems in land-uses categories, to determine their carbon stocks (vegetation and soil), and to quantify CO2 emissions and removal related to their management at the different stages of road construction projects. The procedure is illustrated through its application in the impact assessment of road projects in the territory of Spain. This methodology integrates currently available information on carbon stocks and considers the accounting criteria adopted in national GHG emissions inventories. It is intended to constitute part of an integral assessment tool for GHG emissions in linear infrastructure projects. Four case studies are presented in which emissions from the disruption of environmental systems range from 0.55 to 3.66 kT CO2 km−1. This represents 5 to 13% of the total emissions in the construction stage, and 3.5 to 7% of the net CO2 balance, i.e., once the initial carbon sequestration by restoration planting has been discounted. Results also indicate that under ideal conditions the long-term effect of restoration may even fully offset this impact, though really such conditions are far from being the case in the usual development of plantations. This study confirms the advisability of systematically incorporating the analysis of land use and land-use changes into the assessment of GHG emissions of road projects for consideration in decision-making from the design stage to the maintenance stage in such projects.