This study provides a new methodology developed by the JRC IES and IE for estimating changes in soil carbon stocks and GHG emissions resulting from global land use changes caused by the production of biofuels.
The first part of this work describes the methodology to spatially allocate extra cropland demand derived from results of the economic models. The spatial allocation process is based on a two-step approach:
a) Creation of database (e.g. land use/crop cover/soil types etc.), combining different data sources into a single harmonised database
b) Simulation based on cropland demands from the general equilibrium model MIRAGE (run by IFPRI)¿ and on cropland demand from the partial equilibrium model AGLINK-COSIMO (run by JRC-IPTS).
For this work a dedicated set of spatial data layers was developed. Global cropland data for 2000 (used as the reference year) are merged with land cover data, adjusting the proportions to fully cover an area with land use and cover types whilst keeping the reference data constant. Extra cropland demand is calculated by subtracting the amount of cropland between the different scenarios in 2020, as estimated by the agro-economic models.
In the simulation process data on land cover change (between 2001 and 2004) are used to identify, for each economic regio, how much savannah, grassland, shrubland and forest are converted into new cropland. Cropland demand for individual crops and aggregated crop classes are spatially allocated to grid-cells (of approximately 85 km2 at mid-latitude) using the criteria of land suitability, and distance from existing cropland. In areas of equal land suitability and equal distance to cropland a random factor is introduced to spread out the new cropland uniformly. Crops with an increase in demand are first allocated to existing cropland that is released by crops with a reduction in demand. The remaining demand is allocated to new agricultural land. When cropland expansion occurs within a grid-cell, the corresponding amount of hectares is released from other land cover types present in the cell. The outcome of the spatial allocation process is a set of land use maps describing the estimated shares of each crop or group of crops according to different biofuel scenarios. These maps are combined to produce a single land use map that identifies where in the world Land Use Change (LUC) is likely to occur. This information is then used to estimate, in the second part of the methodology, the changes in land carbon stock and the related GHG emissions (N2O and Above and Below-Ground Biomass emissions).
The methodology for calculating land carbon stock is based on the Tier 1 approach as developed under the IPCC 2006 Guidelines for National Greenhouse Gas Inventories. The method applied to estimate carbon emissions from the soil is to use changes in carbon stocks and treat all changes as emissions. It is based on specifying default values for carbon stocks and using coefficients of divergence from the default values according to land use and land cover.
Finally the land use maps enable an estimation of N2O and Above and Below-Ground Biomass emissions that result from a given change in biofuel demand.