Methodological Differences in ReCiPe 2016 - Water Use impacts between Earthster and Ecoinvent
This document explains the key differences in how Earthster and the Ecoinvent database calculate water use impacts within the ReCiPe2016 framework. These differences can lead to variations in impact scores, particularly for water-intensive products and processes.
1. Assigning Characterization Factors to Water Flows
Ecoinvent: Focuses on water evaporation as the main driver of impact. Assigns characterization factors (CFs) of +1 to water emissions to air ("Water emission/air"), considering this as water lost from the system.
Earthster: Adopts a more conservative approach by assigning CFs of +1 to water used as a resource (e.g., "Water, fresh resource/water/fresh water body"). This includes even unspecified water sources, leading to potentially higher initial impact scores.
2. Accounting for Water Returned to Freshwater Sources
Ecoinvent: Does not explicitly account for water returned to freshwater sources in its impact assessment.
Earthster: Assigns negative CFs to water returned to freshwater sources, acknowledging that this water is not consumed and remains available within the watershed. This aligns with the ReCiPe2016 definition of water consumption, which excludes water returned to the origin.
3. Moderate Assumptions in Earthster
To address the potential for overestimation due to the conservative approach, Earthster offers an alternative set of impact categories with "moderate assumptions." This involves:
Assigning -1 CFs to emissions of unspecified water to unspecified water bodies (e.g., "Water emission/water").
This brings the magnitude of water use impacts closer to Ecoinvent, although differences remain due to the fundamental difference in assigning CFs.
4. Impact on Overall Results
These methodological differences can lead to:
Higher water use impacts in Earthster for products that incorporate water (e.g., agricultural products due to irrigation). This is because the impact is assigned upstream at the point of water uptake.
Higher water use impacts in Ecoinvent for waste management processes where water evaporation is significant.
5. Earthster's Alignment with ReCiPe2016
While both approaches interpret ReCiPe2016, Earthster's methodology, particularly with moderate assumptions, arguably aligns more closely with the guideline's definition of water consumption. This is because it explicitly considers water returned to the source and the incorporation of water into products.
6. Implications for Damage to Ecosystems and Human Health
The differences in water use impact calculation also affect the "Damage to ecosystems" and "Damage to human health" categories, as water use heavily influences these areas.
7. Choosing the Right Impact Categories in Earthster
Users of Earthster can choose between the standard and "moderate assumptions" impact categories depending on their specific needs and preferences. The "moderate assumptions" categories may provide a more balanced comparison with Ecoinvent results.