Journal Article

Quantifying Aspect‐Dependent Snowpack Response to High‐Elevation Wildfire in the Southern Rocky Mountains

Elder, Kelly, Reis, Wyatt, Kampf, Stephanie, McGrath, Daniel, Rey, David

2024

Overview

Increasing wildfire frequency and severity in high‐elevation seasonal snow zones presents a considerable water resource management challenge across the western United States (U.S.). Wildfires can affect snowpack accumulation and melt patterns, altering the quantity and timing of runoff. While prior research has shown that wildfire generally increases snow melt rates and advances snow disappearance dates, uncertainties remain regarding variations across complex terrain and the energy balance between burned and unburned areas. Utilizing paired in situ data sources within the 2020 Cameron Peak burn area on the Front Range of Colorado, U.S., during the 2021–2022 winter, we found no significant difference in peak snow water equivalent (SWE) magnitude between burned and unburned areas. However, the burned south aspect reached peak SWE 22 days earlier than burned north. During the ablation period, burned south melt rates were 71% faster than unburned south melt rates, whereas burned north melt rates were 94% faster than unburned north aspects. Snow disappeared 7–11 days earlier in burned areas than unburned areas. Net energy differences at the burned and unburned weather station sites were seasonally variable, the burned area snowpack lost more net energy during the winter, but gained more net energy during the spring. Increased incoming shortwave radiation at the burned site was 6x more impactful in altering the net shortwave radiation balance than the decline in surface albedo. These findings emphasize the need for post‐wildfire water resource planning that accounts for aspect‐dependent differences in energy and mass balance to accurately predict snowpack storage and runoff timing. Plain Language Summary Wildfires are burning more frequently at high‐elevations, where they modify the snowpack. This complicates efforts to predict when snowmelt runoff will occur and the amount of water that will melt from the snowpack. Wildfire generally causes snow to melt earlier in the year and at a faster rate. However, in complex, mountainous terrain, it is not well understood how the magnitude of these changes may differ between neighboring slopes. During the 2021–22 winter in the Cameron Peak burn area (2020) in Colorado, we found that in a high‐elevation snowpack there was no difference in the amount of water accumulated in the snowpack between areas that were burned by the fire and areas that were not. But in areas that burned, the amount of water in the snowpack reached its largest amount 22 days earlier than the areas that did not burn. The snowpack melted faster on both south and north facing slopes in the burned area than comparable unburned areas, causing the burned areas to be snow free 7–11 days earlier. These results highlight the need to account for complex terrain in water resource planning. Key Points The burned south site reached peak snow water equivalent 22 days earlier than all other sites, which peaked simultaneously Burned site melt rates were similar across aspects but exceeded unburned sites by ∼9 mm d−1, causing snow disappearance ∼9 days earlier Burned site net energy balance was dominated by longwave radiation losses in winter and shortwave radiation gains in spring

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Ablation / Albedo / Colorado / Elevation / Energy balance / landscapes / Mass balance / Moisture content / Mountains / Radiation / Radiation balance / Resource management / Runoff / Short wave radiation / shortwave radiation / Snow / Snow accumulation / Snow-water equivalent / Snowmelt / Snowmelt runoff / Snowpack / spring / Terrain / topographic aspect / Water content / water management / Water resources / Water resources management / Water resources planning / Weather stations / wildfire / Wildfires / Winter