We present simulations of impacts of climate change on forests and other terrestrial ecosystem vegetation cover types in the conterminous USA using the MC2 dynamic global vegetation model (DGVM), as part of an effort coordinated by U.S. Environmental Protection Agency’s (EPA’s) Office of Atmospheric Programs, and intended to inform the fourth National Climate Assessment (NCA4) of the U.S. Global Change Research Program (USGCRP). MC2 DGVM was developed by the U.S. Forest Service’s (USFS) Pacific Northwest Research Station, and it simulates changes in future terrestrial ecosystem vegetative cover, including shifts in vegetation types over time, and burned area across the contiguous U.S. in the 21st century.
Results/Conclusions
The MC2 model was driven by newly published 1/16th degree resolution LOCA (Localized Constructed Analogs) downscaled climate datasets derived from CMIP5 RCP4.5 and RCP8.5 climate change projections. MC2 results project generally increasing carbon uptake by forests under warming temperatures, partly offset by increased fire activities. In some places, MC2 simulates vegetation type conversion leading to reduced fire frequencies. Carbon flux projections in the contiguous U.S. fluctuate and are highly variable by GCM, with the magnitude and even directionality (from sinks to sources) of impacts varying over time under both RCPs. Through the end of the century, national terrestrial ecosystem carbon storage is projected to increase by 3.0 billion metric tons under RCP8.5 and 0.36 billion metric tons under RCP4.5. Under RCP8.5, wildfire acres burned in the contiguous U.S. are projected to remain consistent with rates observed over the past several decades, but moderately decrease under RCP4.5, with changes under both scenarios driven by shifts in vegetation over time.