One method to investigate these feedbacks is field manipulation experiments in which an aspect of the ecosystem state is intentionally perturbed and environmental conditions are subsequently monitored over a period of years to study the response (e.g.
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Biogeophysical processes simulated in CLM4 include solar and longwave radiation interactions with vegetation canopy and soil, momentum and turbulent fluxes from canopy and soil, heat transfer in soil and snow, hydrology of canopy, soil, and snow, and stomatal physiology and photosynthesis.
The snow model contains up to five varying thickness layers and represents processes such as accumulation, melt, compaction, water transfer across layers, and snow aging and aerosol deposition which control snow albedo.
Surface albedo is prognostic and is a function of vegetation reflectivity and transmissivity (each plant functional type, PFT, has unique specified optical properties), exposed (i.e.
proportion of vegetation that is not covered by snow) leaf area and stem area indices (LAI, SAI), ground albedo, the fraction of ground covered by snow, and snow albedo.
When we account for blowing-snow redistribution from grassy-tundra to shrubs, shifts in snowpack distribution in low versus high shrub area simulations counter the climate warming impact, resulting in a grid cell mean ALT that is unchanged.
These results reinforce the need to consider vegetation dynamics and blowing-snow processes in the permafrost thaw model projections. In order for reliable projections of future permafrost degradation to be made, permafrost stability in response to both the direct impacts of warming and other climatic changes (e.g.However, in an idealized pan-Arctic 20% shrub area experiment, atmospheric heating, driven mainly by surface albedo changes related to protrusion of shrub stems above the spring snowpack, leads to soil warming and deeper ALT (~ 10 cm).Therefore, if climate feedbacks are considered, shrub expansion may actually increase rather than decrease permafrost vulnerability.However, several studies indicate that a large-scale pan-Arctic expansion of deciduous shrubs is likely to be a positive feedback onto warming. They conclude that terrestrial amplification of high-latitude warming will likely become more pronounced if shrub area continues to expand.In an idealized climate modeling study in which Arctic shrub area is artificially increased by ~ 20%, Bonfils (2011) found that shrubs warm the Arctic atmosphere through a surface albedo feedback, primarily related to lower surface albedos in spring when shrubs protrude above the snowpack, combined with an evapotranspiration-induced increase in atmospheric moisture content.In their experiment, shrubs () were removed from a 10 m diameter study plot in northeast Siberia.