Carbon Dynamics in the Western United States from 1992 to 2050

Efforts on quantifying carbon dynamics in the western United States are rare and results remains highly uncertain. Major challenges include quantifying historical and future land cover and land use change, understanding spatial and temporal variability of the carbon biogeochemical cycle, and scaling from processes from sites to regions using biogeochemical models. As a component of the USGS effort in assessing potentials of carbon sequestration and greenhouse gas emissions reduction across the country, we quantified carbon dynamics in the western U.S. from 1992 to 2050. Historical land cover and land use change (LCLUC) was reconstructed using satellite-derived maps and the FOREcasting SCEnario of land-use change (FORE-SCE) model. Future LCLUC scenarios were projected according to the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) and downscaled to 250-m resolution. Carbon dynamics in the western U.S. were simulated using the USGS General Ensemble Biogeochemical Modeling System (GEMS) framework. Results show high spatial variability of carbon storage and fluxes in vegetation and soils. The western U.S. has been a carbon sink. However, the sink strength is expected to decline into the future. Estimates of carbon storage change strongly depend on biogeochemical models, geographic locations, disturbances, and IPCC scenarios.