Postfire Snow Albedo and Forest Structure Recovery Drive Decadal
Watershed Scale Reductions in Snow-Water Storage and Snow Retention
Abstract
Forest fires darken snow albedo and degrade forest structure altering
snowpack energy balance, peak snow volume and snowmelt timing for up to
15 years following burn. To date, three-dimensional volumetric estimates
of postfire effects on snow hydrology over the course of postfire
recovery have not been quantified at the watershed scale. Here we
present an improved parameterization of recovery of forest fire effects
on snow hydrology. Using a spatially-distributed snow mass and energy
balance model called SnowModel, we estimate volumetric shifts in
snow-water storage and snowmelt timing across a chrono-sequence of eight
burned forests occurring between 2000 and 2019. One to three years
following fire, postfire effects reduced peak snow-water storage by
8.42% on average (sd = 9.38%) and advanced snow disappearance date by
34 days on average (sd = 7 days). Magnitudes of snow disappearance date
advances tended to decline over recovery relative to the losses observed
immediately following fire. Postfire reductions in peak snow-water
equivalent (SWE) tended to decrease immediately following fire, and
generally recovered over 15 years postfire, but then increased again 4
to 9 years later. Postfire reductions on peak SWE summed over the
15-year postfire recovery period were up to eighteen times greater than
the losses incurred in the first winter following fire alone. Beyond 15
years following fire, postfire effects on snow persisted due to the
postfire shift from forest to open meadow.