Model catalogue: models and modelling approaches for assessing SOC stock changes and GHG emissions

This report (MARVIC D3.2) presents the MARVIC Model Catalogue, an effort to synthesise and structure the large diversity of models currently available for the quantification of soil organic carbon (SOC) stock changes, greenhouse gas (GHG) emissions (i.e. N2O), vegetation development, and ecosystem processes relevant for Monitoring, Reporting and Verification (MRV) systems for carbon farming. The catalogue was developed to support the identification of suitable models for different Land Use and Soil Types (LUSTs) and MRV applications, by facilitating transparent model comparison and informed model selection.

The catalogue is mainly intended for scientists, MRV developers, and technical experts involved in the development and implementation of operational processing chains for carbon farming and greenhouse gas accounting. The catalogue is particularly relevant for researchers working on soil carbon and ecosystem modelling (e.g. performance testing, model evaluation), remote sensing assimilation, and uncertainty assessment, as well as for organizations and technical bodies supporting MRV systems under carbon farming and CRCF-related initiatives.

The catalogue was developed through a comprehensive literature review combined with expert knowledge from the MARVIC consortium. Information was collected from peer-reviewed articles, model documentation, technical reports, and existing model intercomparison studies. Models were organised into eight categories: Soil Carbon, Soil Carbon and N₂O, Soil N₂O only, Arable land, Grassland, Agroforestry, Peatland, and Ecosystem models.

For each model category, information was harmonised into a structured framework including general information, model characteristics, domain of applicability, input data requirements, Earth Observation (EO) integration, outputs simulated, scope of the model, and performance assessment. Particular attention was given to documenting evaluation procedures, pedoclimatic conditions of application, management systems represented, and the integration of remote sensing and EO products where applicable. The catalogue identified and profiled over 100 model entries, including original models and their derivations or variants, covering a wide range of modelling philosophies and application domains. The collected models span nearly nine decades of development, from early SOC models published in the 1930s to recent microbial-explicit and EO-integrated modelling approaches.
Key findings include:

• A strong diversity of models, ranging from relatively simple SOC turnover models to complex ecosystem models coupling carbon, nitrogen, water, and energy fluxes.
  Deliverable 3.2 Model catalogue
• A predominance of models evaluated under temperate arable land conditions, although several models were also assessed under tropical, boreal, Mediterranean, and multi-site/global contexts.
• Increasing integration of remote sensing and EO products in recent modelling approaches, particularly within arable land applications.

The MARVIC Model Catalogue contributes to reducing the complexity associated with the large diversity of available modelling approaches by organising and harmonising key information relevant for model selection and comparison. The catalogue facilitates the identification of models adapted to specific pedoclimatic regions, land-use systems, management practices, and operational constraints. It also provides a basis for future model evaluation and uncertainty assessment activities within MARVIC, particularly regarding EO integration, operational scalability, and model benchmarking. Because modelling approaches and EO capabilities continue to evolve rapidly, the catalogue should be considered a living resource that will be further expanded and updated throughout the project.

Although the catalogue does not provide direct policy recommendations, it supports the implementation of the CRCF and broader carbon farming initiatives by improving transparency regarding the breadth, applicability, and evaluation status of available modelling approaches. The catalogue may assist technical stakeholders and policy-support organisations involved in the development of robust MRV systems adapted to different environmental and agricultural contexts. The MARVIC Model Catalogue represents a structured synthesis of current modelling approaches relevant for SOC, GHG, and ecosystem monitoring in MRV applications. By harmonising information across a large diversity of models and application domains, the catalogue supports transparent model selection, comparison, and future operational developments within MARVIC, and may contribute to the development of more scientifically robust MRV systems, adapted to the diversity of European agricultural systems and pedoclimatic conditions. Future work will continue expanding the catalogue, particularly regarding underrepresented LUSTs, EO integration, uncertainty assessment, and operational benchmarking of candidate models for MRV-oriented processing chains.