Snow darkening effects of black carbon and dust across the Rocky Mountains of the western United States: Experiments using WRF-Chem

Black Carbon (BC) and mineral dust exert a non-neglible radiative forcing when deposited on snowpack by increasing its absorptivity and leading to increased snowmelt (the snow darkening effect; SDE). We study this problem during water year 2009 by using WRF coupled with a sophisticated chemistry model (WRF-Chem). Special to this study is coupling of the SNow, ICe, and Aerosol Radiative model into the land surface model, which treats the process of snow darkening and snow aging by BC and dust. Our simulations, run at ~3.3 km grid spacing, reveal that there is large heterogeneity in the meteorological perturbations associated with BC- and dust-induced SDE, with anomalous warming during the springtime. This warming results in accelerated runoff rates during this period, followed by decreases in runoff during the late spring and summer months. Because agriculture in the United States depends heavily on the water resources associated with the timed-release of seasonal snowmelt, understanding this problem in a high-resolution modelling framework is of great interest.