Abstract
Abstract. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is run to quantify the in-snow and atmospheric radiative effects of black carbon (BC) and dust on a convective-allowing (4 km) grid for water year 2009 across a large area of the Rocky Mountains. The snow-darkening effect (SDE) due to the deposition of these light-absorbing particles (LAPs) on surface snow enhances snowmelt by 3 to 12 mm during late spring and early summer, effectuating surface runoff increases (decreases) prior to (after) June. Meanwhile, aerosol–radiation interactions (ARIs) associated with LAPs generally dim the surface from incoming solar energy, introducing an energy deficit at the surface and leading to snowpack preservation by 1 to 5 mm. Surface runoff alterations brought forth by LAP ARI are of opposite phase to those associated with LAP SDEs, and the BC SDE drives a majority of the surface energy and hydrological perturbations. More generally, changes in snow water equivalent (SWE) brought forth by LAP effects are more a result of perturbations to the surface energy budget rather than changes in precipitation amount or type. It is also found that perturbations to the surface energy budget by dust ARI can differ in sign from those of BC ARI, with the former being positive, enhancing snow melting, and changing runoff.
Highlights
The arid Rocky Mountains of the western United States (WUS) receive most of their precipitation in the form of snowfall from October through March
control experiment (CNT) is warmer than NOCHEM, both simulations have r values of +0.98 compared to snow telemetry (SNOTEL)
Using seven branch WRF-Chem experiments with a horizontal resolution of 4 km, the snow-darkening effect (SDE) of lightabsorbing particles (LAPs) were quantified across four subregions of the WUS for water year 2009
Summary
The arid Rocky Mountains of the western United States (WUS) receive most of their precipitation in the form of snowfall from October through March. The resulting snowpack forms a network of natural mesoscale storage reservoirs that provide approximately 80 % of the surface water across the region during the warm season (Serreze et al, 1999; Hamlet et al, 2007). There have been observed changes in the hydrology across the WUS associated with external climate forcings (e.g., anthropogenic climate change) that may be acting to compromise the security of water resources across the region and beyond (Hamlet et al, 2007; Kapnick and Hall, 2012; Fyfe et al, 2017; Mote et al, 2018). Forced warming associated with greenhouse gases and lightabsorbing particles (LAPs; Pierce et al, 2008) and LAP deposition on snowpack (Flanner et al, 2007; Qian et al, 2009, C. Wu et al, 2018; Sarangi et al, 2019), rather than natural
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