Articles | Volume 9, issue 9
Model description paper
02 Sep 2016
Model description paper |  | 02 Sep 2016

Downscaling land use and land cover from the Global Change Assessment Model for coupling with Earth system models

Yannick Le Page, Tris O. West, Robert Link, and Pralit Patel

Abstract. The Global Change Assessment Model (GCAM) is a global integrated assessment model used to project future societal and environmental scenarios, based on economic modeling and on a detailed representation of food and energy production systems. The terrestrial module in GCAM represents agricultural activities and ecosystems dynamics at the subregional scale, and must be downscaled to be used for impact assessments in gridded models (e.g., climate models). In this study, we present the downscaling algorithm of the GCAM model, which generates gridded time series of global land use and land cover (LULC) from any GCAM scenario. The downscaling is based on a number of user-defined rules and drivers, including transition priorities (e.g., crop expansion preferentially into grasslands rather than forests) and spatial constraints (e.g., nutrient availability). The default parameterization is evaluated using historical LULC change data, and a sensitivity experiment provides insights on the most critical parameters and how their influence changes regionally and in time. Finally, a reference scenario and a climate mitigation scenario are downscaled to illustrate the gridded land use outcomes of different policies on agricultural expansion and forest management. Several features of the downscaling can be modified by providing new input data or changing the parameterization, without any edits to the code. Those features include spatial resolution as well as the number and type of land classes being downscaled, thereby providing flexibility to adapt GCAM LULC scenarios to the requirements of a wide range of models and applications. The downscaling system is version controlled and freely available.

Short summary
A computer program was developed to transform maps of regional land use (e.g., crops) and land cover (e.g., forests) areas into gridded maps actually representing their spatial distribution within each region. This is important for studies of future environmental change: economic models project agricultural activities at the regional scale, but Earth system models need gridded information to project the impact of such activities on climate, biodiversity, water availability, and other aspects.