edges is a library allowing flexible Life Cycle Impact Assessment (LCIA) for the brightway2/brightway25 LCA framework.

Unlike traditional LCIA methods that apply characterization factors (CFs) solely to nodes (e.g., elementary flows), edges applies CFs directly on the edges — the exchanges between suppliers and consumers — allowing for more precise and context-sensitive impact characterization.

This approach enables LCIA factors to reflect the specific context of each exchange, including parameters such as:

• Geographic region of production and consumption
• Magnitude of flows
• Scenario-based parameters (e.g., changing atmospheric conditions)

The edges Python library offers a novel approach to applying characterization factors (CFs) during the impact assessment phase of Life Cycle Assessment (LCA). Unlike conventional methods that uniformly assign CFs to nodes (e.g., processes like Water, from well in the brightway2 ecosystem), edges shifts the focus to the edges—the exchanges or relationships between nodes. This allows CFs to be conditioned based on the specific context of each exchange. Essentially, edges introduces unique values in the characterization matrix tailored to the characteristics of each edge.

By focusing on edges, the library incorporates contextual information such as the attributes of both the supplier and the consumer (e.g., geographic location, ISIC classification, amount exchanged, etc.). This enables a more detailed and flexible impact characterization, accommodating parameters like the location of the consumer and the magnitude of the exchange.

Furthermore, edges supports the calculation of weighted CFs for both static regions (e.g., RER) and dynamic regions (e.g., RoW), enhancing its ability to model complex and region-specific scenarios.

• Edge-based CFs: Assign CFs specifically to individual exchanges between processes.
• Geographic resolution: Supports 346 national and sub-national regions.
• Scenario-based flexibility: Incorporate parameters (e.g., CO₂ atmospheric concentration) directly in CF calculations, enabling dynamic scenario analysis.
• Efficient workflow: Clearly separates expensive exchange-mapping tasks (performed once) from inexpensive scenario-based numeric CF evaluations.

Currently, the library provides regionalized CFs for:

• AWARE 2.0 (water scarcity impacts)
• ImpactWorld+ 2.1
• GeoPolRisk 1.0
• GLAM3 Land use impacts on biodiversity

You can install the library using pip:

pip install edges

• Documentation

Check out the examples' notebook.

    
from edges import get_available_methods

# Get the available methods
methods = get_available_methods()
print(methods)

import bw2data
from edges import EdgeLCIA

# Select an activity from the LCA database
act = bw2data.Database("ecoinvent-3.10-cutoff").random()

# Define a method
method = ('AWARE 2.0', 'Country', 'unspecified', 'yearly')

# Initialize the LCA object
LCA = EdgeLCIA({act: 1}, method)
LCA.lci()

# Map CFs to exchanges: apply suggested strategies
LCA.apply_strategies()

# or apply these strategies manually
#LCA.map_exchanges()

# If needed, extend the mapping to aggregated and `dynamic` regions (e.g., RoW)
#LCA.map_aggregate_locations()
#LCA.map_dynamic_locations()
#LCA.map_contained_locations()

# add global CFs to exchanges missing a CF
#LCA.map_remaining_locations_to_global()

# Evaluate CFs
LCA.evaluate_cfs()

# Perform the LCIA calculation
LCA.lcia()
print(LCA.score)

# Optional but recommended: print a dataframe with the characterization factors used
# this allows you to check whether exchanges have been given the correct CFs
# include_unmatched=True allows you to see which exchanges were not matched (and if some should have been)
LCA.generate_cf_table()

Consider the following LCIA data file (saved under gwp_example.json)`:

{
  "name": "Example LCIA Method",
    "version": "1.0",
    "description": "Example LCIA method for greenhouse gas emissions",
    "unit": "kg CO2e",
    "exchanges": [
      {
        "supplier": {
          "name": "Carbon dioxide",
          "operator": "startswith",
          "matrix": "biosphere"
        },
        "consumer": {
          "matrix": "technosphere",
          "type": "process"
        },
        "value": "1.0"
      },
      {
        "supplier": {
          "name": "Methane, fossil",
          "operator": "contains",
          "matrix": "biosphere"
        },
        "consumer": {
          "matrix": "technosphere",
          "type": "process"
        },
        "value": "28 * (1 + 0.001 * (co2ppm - 410))"
      },
      {
        "supplier": {
          "name": "Dinitrogen monoxide",
          "operator": "equals",
          "matrix": "biosphere"
        },
        "consumer": {
          "matrix": "technosphere",
          "type": "process"
        },
        "value": "265 * (1 + 0.0005 * (co2ppm - 410))"
      }
  ]
}

We can perform a parameter-based LCIA calculation as follows:

import bw2data
from edges import EdgeLCIA

# Select an activity from the LCA database
bw2data.projects.set_current("ecoinvent-3.10.1-cutoff")
act = bw2data.Database("ecoinvent-3.10.1-cutoff").random()
print(act)

# Define scenario parameters (e.g., atmospheric CO₂ concentration and time horizon)
params = {
    "some scenario": {
         "co2ppm": {"2020": 410, "2050": 450, "2100": 500}, "h": {"2020": 100, "2050": 100, "2100": 100}
    }
}

# Define an LCIA method (symbolic CF expressions stored in JSON)
method = ('GWP', 'scenario-dependent', '100 years')

# Initialize LCIA
lcia = EdgeLCIA(
   demand={act: 1},
   filepath="lcia_example_3.json",
   parameters=params
)

# Perform inventory calculations (once)
lcia.lci()

# Map exchanges to CF entries (once)
lcia.map_exchanges()

# Optionally, resolve geographic overlaps and disaggregations (once)
lcia.map_aggregate_locations()
lcia.map_dynamic_locations()
lcia.map_remaining_locations_to_global()

# Run scenarios efficiently
results = []
for idx in {"2020", "2050", "2100"}:
    lcia.evaluate_cfs(idx)
    lcia.lcia()
    df = lcia.generate_cf_table()

    scenario_result = {
        "scenario": idx,
        "co2ppm": params["some scenario"]["co2ppm"][idx],
        "score": lcia.score,
        "CF_table": df
    }
    results.append(scenario_result)

    print(f"Scenario (CO₂ {params['some scenario']['co2ppm'][idx]} ppm): Impact = {lcia.score}")

See Methods from Documentation.

See Theory from Documentation.

Contributions are welcome! Please follow these steps to contribute:

1. Fork the repository.
2. Create a new branch for your feature or fix.
3. Commit your changes.
4. Submit a pull request.

This project is licensed under the MIT License. See the LICENSE.md file for more information.

For any questions or inquiries, please contact the project maintainer at [email protected].

• Romain Sacchi
• Alvaro Hahn Menacho
• Raphaël Jolivet - contributed to the CLIPSpy-based rule engine implementation.

The development of this library was supported by the French agency for Energy ADEME, via the financing of the HySPI project. The HySPI project aims to provide a methodological framework to analyze and quantify, in a systemic and prospective manner, the environmental impacts of the decarbonization strategy of hydrogen production used by the industry in France. We also acknowledge financial support from the Europe Horizon project RAWCLIC as well as the Europe Horizon project PRISMA.