Measuring the Effect of Forest Fires on Daily Snow Albedo Across Spatial and Temporal Scales Using MODIS Data

Abstract:

The majority of water resources in the western US originate in seasonal snow. Snow-water storage is vulnerable due to climate change and the associated increase in wildfire season, size, and intensity largely due to the reduction of snow albedo as a result of the production and deposition of light absorbing impurities (LAI), particularly black carbon. Using Moderate Resolution Imaging Spectroradiometer (MODIS) and Monitoring Trends in Burn Severity (MTBS) data we evaluated daily snow surface albedo before and after fire occurrence across a chronosequence of burned forests (burned 1-20 years before present) in the Triple Divide region of western Wyoming. This area is especially important in the western US because it forms the headwaters of the Columbia, Colorado, and Missouri Rivers. Snow surface albedo was evaluated using zonal statistics across the burn perimeter, as well as with high severity burn, moderate severity burn, and unburned forest classes. We observed an initial shift in the snow surface albedo immediately following fire occurrence, due to the loss of forest density and increase exposure of the snow surface. However, the snow albedo was lower overall and particularly within high severity burned areas, relative to nearby unburned open, snow-covered meadows. Decreased snow albedo accelerates snowmelt across burned forested headwater regions for at least 10 years following fire occurrence, altering the volume of snow-water storage, the timing of snowmelt, and associated availability of downstream water resources.