Why are we studying biomass residue?
California faces a crisis across its forested landscapes. Increased drought, record-breaking heat waves, and high winds, are together driving severe wildfire conditions in biomass-dense forests. In light of this ongoing emergency — with its ecological, economic, climate, and public health implications — California is prioritizing a range of forest management solutions. The state’s goal is to treat one million acres of forest per year via thinning, prescribed burns, and other management practices.
These newer efforts, on top of ongoing commercial logging activities, generate millions of tons of woody residues each year. Woody residues typically remain in the field, and may be piled or burned onsite — impacting air quality, exacerbating wildfire risk, and leading to further ecosystem disruption. State policymakers have turned to bioelectricity generation as a key market for woody biomass, in the hope that it can support sustainable forest management while also advancing California’s Renewable Portfolio Standard goals. However, many people are concerned about the impact of bionergy systems on air quality, climate, and ecosystem health. In particular, uncertainty around the comparative climate impacts of bioelectricity versus pile burning and other in-field strategies has often made it difficult to determine the best pathways for managing forest residues.
Our new C-BREC model aims to illuminate these emissions impacts, and to provide site-specific analyses to guide management choices. We are currently working with policymakers and forest and fire managers to deploy C-BREC to improve the climate outcome of state policies including the BioMAT Feed-in Tariff, the Low Carbon Fuel Standard, and the Forest Health Grant program.
The C-BREC model
The California Biomass Residue Emissions Characterization (C-BREC) model provides a life-cycle assessment framework for the use of California forest residues for electricity generation. Further planned work will extend this framework to evaluate other use-cases for woody residues such as liquid fuels and wood products.
The C-BREC model enables robust, transparent accounting for greenhouse gas and air pollutant emissions associated with residual woody biomass energy systems in California. Users specify the following key project characteristics:
- Location of residue generation
- Type of forest treatment or harvest activity being conducted and baseline residue disposition
- Location of residue utilization
- Reference fate of unremoved biomass (prescribed burn, left in place)
- Key supply chain characteristics such as biomass removal level, any post-harvest treatment, end-use technology, etc.
For a given project profile, the C-BREC model generates an emissions time-series, and reports net CO2-equivalent (CO2e) emission values for two different time-explicit climate metrics. It quantifies the emissions associated directly with a “use” case in which biomass residuals are mobilized from the field to generate bioelectricity, against a “reference” case in which they remain onsite to be burned or left in-field.
The net emissions of the biopower system is the difference between these two fates for the same material. The use case includes emissions from mobilization, transportation, and end-use, while the reference emissions are made up of three distinct processes, applied in probabilistic fashion to any given ton of biomass:
- Pile or broadcast burning of residuals in year 1
- Decay extending for 100 years of material piled/scattered on the forest floor
- Ongoing exposure to wildfire over a 100-year period
Reports and materials
- Delivering Climate and Air Quality Benefits from the Use of Forest Residues in California
- Project brief (2022)
- Climate and air pollution impacts of generating biopower from forest management residues in California
- Environmental Research Letters (2023)
- Final report (2021)
- Interim report (2021)
- Model Framework (2021)
- Criteria Air Pollutant Emissions of Biopower Generation from Forest Residues in California
- Interim report (2021)
The C-BREC model development was funded by a grant from the California Energy Commission (CEC) through its Electric Program Investment Charge (EPIC) program, which supports public interest R&D investments in technologies and solutions that help the electricity sector support California’s energy and environmental goals.