Energy balance and snowmelt drivers of a marginal subalpine snowpack

Abstract

Snowmelt from the seasonal snowpack in the Australian Alps is a significant source of water for irrigated agriculture, electricity generation, and environmental flows in the Murray–Darling Basin. Previous studies have reported negative decadal to multidecadal trends in maximum snow depth, snow season duration, and snow‐covered area. Here, we characterise the energy balance of this marginal maritime snowpack for the first time. Turbulent fluxes measured using the eddy covariance and bulk aerodynamic methods are compared; discrepancies are attributed to the differing assumptions of the methods and characteristics of the measurement site. We examine the variability of the individual energy balance components and the drivers of snowmelt, and we find that incoming longwave radiation is the dominant control on snowmelt, providing more than 80% of the total energy to the snowpack over the season. During a midwinter rain‐on‐snow event, the advected rain heat flux provided 8% of the daily total, with the incoming longwave flux still accounting for almost 80%. The ground heat flux contributes a small proportion of the seasonal total but increases in patchy or intermittent snow cover. Comparing these results with those of studies in other maritime locations, we find that the turbulent fluxes are likely to make a proportionally higher contribution to the energy balance due to the short Australian snow season, underpinning the sensitivity of this environment to climate variability and change. These results extend the limited body of knowledge on highly marginal snowpacks and may be relevant to other regions with no direct measurements of the energy balance.

Spatial controls on the distribution and dynamics of a marginal snowpack in the Australian Alps

“…Temperatures between 0.4 and 1.8°C, conducive to mixed‐phase precipitation according to Chubb et al (), accounted for 27% (223 mm) of the May–October precipitation in 2015 but only 14% (275 mm) in 2016. With respect to ablation, air temperature is related to not only the sensible heat flux but also incoming longwave radiation (Ohmura, ), which Bilish et al () found to be the dominant source of energy to the snowpack at Pipers Creek.…”

“…These include high bulk densities and low vertical temperature gradients. Bilish et al () suggested that the Australian snowpack may have some relevance to understanding snowpack behaviour in the more marginal of global snow regions when no local long‐term measurements exist.…”

“…The upper Pipers Creek catchment covers 1.4 km 2 in Kosciuszko National Park, New South Wales, Australia (Figure 1), and was previously described by Bilish et al (2018). The subalpine catchment extends from 1668 to 1853 m above sea level (asl), and vegetation is predominantly grassland/alpine bog and eucalypt woodland.…”

“…Marginal snowpacks are characterised by high bulk densities and low vertical temperature gradients (Sanecki, Green, Wood, & Lindenmayer, ). Bilish, McGowan, and Callow () described the warm Australian snowpack as event‐driven (p. 3848), with large proportional changes able to take place over short periods of time. Knowledge of marginal snowpacks is particularly important in a warming climate, as regions with wintertime temperatures close to 0°C are highly vulnerable to change (Adam, Hamlet, & Lettenmaier, ; Nolin & Daly, ), with such conditions extending to snowpacks in locations not previously considered marginal as global warming continues (Petersky & Harpold, ).…”

“…Marginal snowpacks are characterised by high bulk densities and low vertical temperature gradients (Sanecki, Green, Wood, & Lindenmayer, 2006). Bilish, McGowan, and Callow (2018) described the warm Australian snowpack as event-driven (p. 3848), with large proportional changes able to take place over short periods of time.…”