During the first year immediately following fire, the annual radiative forcing from
surface albedo change was smaller than the 3-5 year mean. This was because charred
surfaces and exposure of black carbon on the soil surface during the summer after the fire
reduced albedo below that observed at nearby unburned conifer stands (28). After 3-5
years, the establishment of grasses, shrubs, and mosses and other changes to the surface
increased summer albedo above pre-burn levels (Fig. 1). To estimate the radiative forcing
during the first year, we assumed surface albedo within the Donnelly Flats perimeter in
July, August, and September after the June 1999 fire was 0.07 (28). During winter and
spring, and summer we used our observations (e.g., Fig. 1) to estimate surface albedo.
We also assumed that the attenuation of outgoing shortwave radiation by clouds and
atmospheric constituents was the same as for the 2002-2004 period: specifically that the
difference in outgoing shortwave radiation at the tropopause was 60% of the difference at
the surface. This yielded a year 1 albedo-driven radiative forcing of -5.4 ± 2.2 W m-2,
with the error estimate including ± 1.2 W m-2 from uncertainty in the albedo
measurements and ± 1.0 W m-2 from a subjective assessment of the uncertainty
associated with using the CRM.