Recent and Future Anthropogenic Land-Cover Change in the United States and Its Impact on Climate Forcing

Abstract:

Forestry, cultivation, and urbanization result in distinct changes in land-cover, which in turn affect biogeochemical and biogeophysical process. Due to the nature of each type of land conversion, the associated climate forcing response may range from short to long-term, with some persisting for decades or longer. To understand how anthropogenic land cover change may impact the climate system in the future, projections are often developed based on an overarching scenario framework. An increasingly expanding set of land-use change scenarios has been developed to assess global environmental change under a range of alternative storylines. However, utilizing these frameworks at local to regional scales needed for environmental management is problematic due to their coarse spatial and (often) thematic resolution. We have developed techniques to extend global change projections to ecoregions of the conterminous United States, while maintaining coherence at global and local scales. We present a comparison of 1) scenario frameworks, and 2) scenario downscaling methods, and the effect each has on the composition of land-cover over the 21^st century. Second, we demonstrate how historical and future projections of land-cover change impact at the regional scale 1) the capacity of ecosystems to store and sequester carbon, and 2) land-cover albedo induced changes to surface radiative forcing. Downscaled projections for IPCC SRES scenarios and Representative Concentration Pathways were developed along with business-as-usual scenarios based on local scale land-use histories. Three downscaling techniques were explored, where coarse-scale gridded data (half-degree) was allocated to ecoregions based on 1) an area weighting method, 2) land-cover composition, and 3) land-use histories. Each resulting scenario was then simulated using stochastic Monte Carlo methods within a state and transition simulation model. In addition to land-cover change, we also tracked changes across a range of carbon stocks and fluxes, and changes in surface radiative forcing. This comparative assessment provides important insight into the use of global-scale scenarios at regional scales.