Impacts of absorbing aerosol deposition on snowpack and hydrologic cycle in the Rocky Mountain region based on variable-resolution CESM (VR-CESM) simulations
The deposition of light-absorbing aerosols (LAAs), such as black carbon (BC) and dust, onto snow cover has been suggested to reduce the snow albedo and modulate the snowpack and consequent hydrologic cycle. In this study we use the variable-resolution Community Earth System Model (VR-CESM) with a...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/511/2018/acp-18-511-2018.pdf |
| Summary: | The deposition of light-absorbing aerosols (LAAs), such as black carbon (BC) and
dust, onto snow cover has been suggested to reduce the snow albedo and
modulate the snowpack and consequent hydrologic cycle. In this study we use
the variable-resolution Community Earth System Model (VR-CESM) with a
regionally refined high-resolution (0.125°) grid to quantify
the impacts of LAAs in snow in the Rocky Mountain region during the period
1981–2005. We first evaluate the model simulation of LAA concentrations both
near the surface and in snow and then investigate the snowpack and runoff
changes induced by LAAs in snow. The model simulates similar magnitudes of
near-surface atmospheric dust concentrations as observations in the Rocky
Mountain region. Although the model underestimates near-surface atmospheric
BC concentrations, the model overestimates BC-in-snow concentrations by
35 % on average. The regional mean surface radiative effect (SRE) due to LAAs
in snow reaches up to 0.6–1.7 W m<sup>−2</sup> in spring, and dust contributes to
about 21–42 % of total SRE. Due to positive snow albedo feedbacks induced
by the LAA SRE, snow water equivalent is reduced by 2–50 mm and snow cover
fraction by 5–20 % in the two regions around the mountains (eastern Snake
River Plain and southwestern Wyoming), corresponding to an increase in
surface air temperature by 0.9–1.1 °C. During the snow melting
period, LAAs accelerate the hydrologic cycle with monthly runoff increases of
0.15–1.00 mm day<sup>−1</sup> in April–May and reductions of 0.04–0.18 mm day<sup>−1</sup> in June–July in the mountainous regions. Of all the mountainous
regions, the Southern Rockies experience the largest reduction of total runoff by
15 % during the later stage of snowmelt (i.e., June and July). Compared to
previous studies based on field observations, our estimation of dust-induced
SRE is generally 1 order of magnitude smaller in the Southern Rockies,
which is ascribed to the omission of larger dust particles (with the diameter
> 10 µm) in the model. This calls for the inclusion of larger
dust particles in the model to reduce the discrepancies. Overall these
results highlight the potentially important role of LAA interactions with
snowpack and the subsequent impacts on the hydrologic cycles across the Rocky
Mountains. |
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| ISSN: | 1680-7316 1680-7324 |