ESRL/PSD Seminar Series

Since 2002, the headwaters of the Colorado River Basin have experienced changes in land cover, occurring at sub-annual timescales. Widespread tree mortality from bark beetle infestation has taken place across a range of forest types, elevation, and latitude. Extent and severity of forest structure alteration have been observed through a combination of aerial survey data, MODIS-derived leaf area index (LAI), and in situ measurements. Additional disturbance has resulted from deposition of dust from regional dryland sources on mountain snowpacks that strongly alter the snow surface albedo, driving earlier and faster snowmelt runoff. Severity of dust-on-snow events have been estimated via satellite, field, and in-situ observations. In this study, we explore the combined impacts of forest disturbance and dust on snow within a hydrologic modeling framework. We force the Distributed Hydrology and Vegetation Model (DHSVM) with observed meteorology, time-varying maps of forest properties to emulate bark beetle impacts, and variable parameterizations of snow albedo based on dust events. Results from beetle-killed canopy alteration suggest slightly greater snow accumulation as a result of less snow interception and reduced canopy sublimation, which outweigh increases in sub-canopy snow ablation fluxes, contributing to overall increases in annual water yield on the order of 10 %. However, understory regeneration roughly halves the changes in water yield. The primary hydrologic control of dust-on-snow events is on the rate of snowmelt, with more rapid melt rates associated with more extreme dust deposition, producing earlier peak streamflow rates for snowmelt dominated catchments on the order of 2 – 3 weeks.