Response of Snow and Land Surface Albedo to Fire Disturbance in the Sierra Nevada over the MODIS Record

Climate change is impacting mid-latitude subalpine environments, from warming temperatures to altered precipitation patterns, leading to increased wildfire potential. In the Sierra Nevada, CA, frequent and consecutive low snow years combined with other natural and anthropogenic factors have contributed to heightened wildfire intensity and frequency. Increasingly, burn scars are overlapping with snow accumulation zones, leading to competing effects on the land surface energy balance; the landscape overall brightens following canopy removal and exposure of snow during winter, but the snow itself is darker from deposition of char and other light absorbing particles. This study characterizes snow and landscape response to fire disturbance by analyzing 20 years of remotely sensed land surface and snow albedo in Sierra Nevada watersheds that have been impacted by high intensity wildfire. Snow albedo is assessed daily using a spatially and temporally complete time series that combines outputs from the MODIS Snow-Covered Area and Grain Size (SCAG) and Dust Radiative Forcing in Snow (DRFS) algorithms. Patterns are interpreted over a coincident time period with the factors that primarily control snow albedo: fractional snow coverage (SCAG), snow grain size (SCAG), and reduction in visible albedo by light absorbing particles (DRFS). Patterns in land surface albedo, the albedo of the full pixel, are analyzed using the 16-day-averaged MODIS product MCD43A3. This research contributes important information about radiative forcing due to wildfire, surface energy balance, and snowpack behavior in water-stressed environments, which is increasingly crucial as wildfires increase in frequency and intensity both in the Sierra Nevada and globally.