Biosphere-climate interactions in a changing climate over North America

This study focuses on projected changes to vegetation characteristics and their interactions with the atmosphere under future climatic conditions over North America, using four transient climate change simulations of the Canadian Regional Climate Model (CRCM5). Here CRCM5 performs dynamical downscaling of the Canadian Earth System Model (CanESM2) simulated data, for Representative Concentration Pathways (RCPs) 4.5 and 8.5. For each RCP, two CRCM5 simulations are performedone with static vegetation phenology and the other with dynamic vegetation phenologyfor the 1950-2100 period over North America. The dynamic vegetation model used here is the Canadian Terrestrial Ecosystem Model. Results show that the extension of the growing season under future climatic conditions in the dynamic phenology simulations leads to higher annual vegetation productivity and biomass. In comparison with projected changes based on CRCM5 with static phenology, CRCM5 with phenology dynamics leads to an albedo-mediated warming enhancement across most of North America in spring. In summer, results suggest a warming enhancement in the northern latitudes and an attenuation of warming for more southern regions due to hydrological feedbacks. Furthermore, results suggest that vegetation enhances its water-use efficiency with rising atmospheric CO2 concentrations. Over southeastern United States, in the dynamic phenology simulation corresponding to the RCP8.5 scenario, the adverse effects of the projected increase in temperatures and decrease in precipitation on vegetation dominate the CO2 fertilization effect, leading to decreasing trends in productivity during the 2071-2100 period. This study thus clearly demonstrates that phenology dynamics modulate greenhouse gas-mediated warming through various biophysical feedbacks.