edges: Edge-based life cycle impact assessment

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.

Key Features

• 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

Installation

You can install the library using pip:

pip install git+https://github.com/Laboratory-for-Energy-Systems-Analysis/edges.git

Getting Started

Check out the examples' notebook.

Check available methods from edges

    
from edges import get_available_methods

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

Perform edge-based LCIA with edges

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 1.2c', 'Country', 'unspecified', 'yearly')

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

# Print a dataframe with the characterization factors used
LCA.generate_cf_table()

Perform parameter-based LCIA

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

[
  {
    "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-cutoff")
act = bw2data.Database("ecoinvent-3.10-cutoff").random()

# Define scenario parameters (e.g., atmospheric CO₂ concentration and time horizon)
params = {"co2ppm": [410, 450, 500], "h": 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="gwp_example.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 range(lcia.scenario_length):
    lcia.evaluate_cfs(idx)
    lcia.lcia()
    df = lcia.generate_cf_table()

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

    print(f"Scenario {idx+1} (CO₂ {params['co2ppm'][idx]} ppm): Impact = {lcia.score}")
    

Data Sources

• AWARE: The AWARE factors are adapted from peer-reviewed sources and tailored to provide precise country-specific data for environmental modeling. Refer to the AWARE website https://wulca-waterlca.org/ for more information.

If you use the AWARE method, please cite the following publication:

@article{boulay2018aware,
  title={The WULCA consensus characterization model for water scarcity footprints: assessing impacts of water consumption based on available water remaining (AWARE).},
  author={Anne-Marie Boulay, Jane Bare, Lorenzo Benini, Markus Berger, Michael J. Lathuillière, Alessandro Manzardo, Manuele Margni, Masaharu Motoshita, Montserrat Núñez, Amandine Valerie Pastor, Bradley Ridoutt, Taikan Oki, Sebastien Worbe & Stephan Pfister },
  journal={Int J Life Cycle Assess},
  volume={23},
  pages={368–378},
  year={2018},
  publisher={Springer}
}

Methodology

1. Exchange Mapping: Identifies the inventory exchanges matching the CF criteria. Matching can be based on any exchange fields (e.g., name, unit, location, classification, etc.).

2. Scenario Evaluation: CF values can be defined numerically or symbolically and may depend on parameters (e.g., co2ppm, time horizons).

3. Characterization Matrix: CFs are applied directly to inventory exchanges in the characterization matrix of Brightway, enabling precise context-based LCIA.

Additionally, for regionalized characterization factors, helping functions are available:

• .map_aggregate_location(): For specific ecoinvent regions (e.g., RER, Canada without Quebec, etc.) that do ont have regionalized CFs, edges computes the weighted average of the characterization factors for the countries included in the region, based either on population or GDP. The weighting key can be selected by the user (weighting by population size by default), or it can be provided within the LCIA method file.

• .map_dynamic_locations(): For relative regions (e.g., RoW, RoE, etc.), edges dynamically defines the locations included in the region based on the mathing activities in the LCA database. The weighted average of the characterization factor of the geographies containd in the region is then computed accordingly.

• .map_disaggregate_locations(): For locations that do not have regionalized CFs, but are part of larger regions that have a regionalized CF, edges will attribute such CF to the exchange.

• .map_remaining_locations_to_global(): For exchanges that do not have a regionalized CF, edges will attribute the global CF to the exchange. The global CF is defined as the weighted-average of the regionalized CFs, based on the weighting key selected.

Contributing

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.

License

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

Contact

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

Contributors

• Romain Sacchi
• Alvaro Hahn Menacho

Acknowledgments

The development of this library was entirely 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.