Combined impacts of current and future dust deposition and regional warming on Colorado River Basin snow dynamics and hydrology

Abstract

Abstract. The Colorado River provides water to 40 million people in seven western states and two countries and to 5.5 million irrigated acres. The river has long been overallocated. Climate models project runoff losses of 5-20 % from the basin by mid-21st century due to human-induced climate change. Recent work has shown that decreased snow albedo from anthropogenic dust loading to the CO mountains shortens the duration of snow cover by several weeks relative to conditions prior to western expansion of the US in the mid-1800s, and advances peak runoff at Lees Ferry, Arizona, by an average of 3 weeks. Increases in evapotranspiration from earlier exposure of soils and germination of plants have been estimated to decrease annual runoff by more than 1.0 billion cubic meters, or ∼ 5% of the annual average. This prior work was based on observed dust loadings during 2005-2008; however, 2009 and 2010 saw unprecedented levels of dust loading on snowpacks in the Upper Colorado River Basin (UCRB), being on the order of 5 times the 2005-2008 loading. Building on our prior work, we developed a new snow albedo decay parameterization based on observations in 2009/10 to mimic the radiative forcing of extreme dust deposition. We convolve low, moderate, and extreme dust/snow albedos with both historic climate forcing and two future climate scenarios via a delta method perturbation of historic records. Compared to moderate dust, extreme dust absorbs 2× to 4× the solar radiation, and shifts peak snowmelt an additional 3 weeks earlier to a total of 6 weeks earlier than pre-disturbance. The extreme dust scenario reduces annual flow volume an additional 1 % (6 % compared to pre-disturbance), a smaller difference than from low to moderate dust scenarios due to melt season shifting into a season of lower evaporative demand. The sensitivity of flow timing to dust radiative forcing of snow albedo is maintained under future climate scenarios, but the sensitivity of flow volume reductions decreases with increased climate forcing. These results have implications for water management and suggest that dust abatement efforts could be an important component of any climate adaptation strategies in the UCRB.

Catchment response to bark beetle outbreak and dust-on-snow in the Colorado Rocky Mountains

“…The full basin-scale modeling studies suggest decreasing annual water yield with increasing dust due to increased evaporative losses. Deems et al (2013) suggest that dust-on-snow impacts may be further exacerbated by projected climate change. Unlike BB impacts, which are restricted to specific forest stands, dust-on-snow impacts are more spatially widespread.…”

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

“…This requires a priori knowledge of spectral absorption and scattering coefficients of ice, which have been well known since the 1980s (Warren, 1982) and recently updated (Warren and Brandt, 2008;. The effects of impurities have been studied many times with particular emphasis on black carbon and certain mineral dusts (Deems et al, 2013;Kaspari et al, 2014;. Aoki et al (2013) and Cook et al (2017) have attempted to incorporate biological impurities into radiative transfer schemes.…”

Exploring the impact of forcing error characteristics on physically based snow simulations within a global sensitivity analysis framework

“…Physically based models allow researchers to test hypotheses about the role of specific processes in hydrologic systems and how changes in environment (e.g., climate, land cover) may impact key hydrologic fluxes and states (Barnett et al, 2008;Deems et al, 2013;Leavesley, 1994;Clark et al, 2011b). Due to the complexity of processes represented, these models usually require numerous meteorological forcing inputs and model parameters.…”