Abstract
Snowmelt contributions to streamflow in mid-latitude mountain basins typically dominate other runoff sources on annual and seasonal timescales. Future increases in temperature and changes in precipitation will affect both snow accumulation and seasonal runoff timing and magnitude, but the underlying and fundamental roles of mountain basin geometry and hypsometry on snowmelt sensitivity have received little attention. To investigate the role of basin geometry in snowmelt sensitivity, a linear snow accumulation model and the Cold Regions Hydrological Modeling (CRHM) platform driven are used to estimate how hypsometry affects basin-wide snow volumes and snowmelt runoff. Area-elevation distributions for fifty basins in western Canada were extracted, normalized according to their elevation statistics, and classified into three clusters that represent top-heavy, middle, and bottom-heavy basins. Prescribed changes in air temperature alter both the snow accumulation gradient and the total snowmelt energy, leading to snowpack volume reductions (10–40%), earlier melt onsets (1–4 weeks) and end of melt season (3 weeks), increases in early spring melt rates and reductions in seasonal areal melt rates (up to 50%). Basin hypsometry controls the magnitude of the basin response. The most sensitive basins are bottom-heavy, and have a greater proportion of their area at low elevations. The least sensitive basins are top-heavy, and have a greater proportion of their area at high elevations. Basins with similar proportional areas at high and low elevations fall in between the others in terms of sensitivity and other metrics. This work provides context for anticipating the impacts of ongoing hydrological change due to climate change, and provides guidance for both monitoring networks and distributed modeling efforts.
Highlights
In mountain basins, winter snowpacks typically represent the dominant component of warm-season streamflows (Cayan, 1996; Beniston, 1997; Barnett et al, 2005; Bales et al, 2006; Pomeroy et al, 2012)
While realworld spatial variations in climate and elevation will affect the response of a specific basin to climate change, hypsometry plays an important role in snowpack volumes and the rates and timing of snowmelt and this has not been addressed in recent global comparative studies using fixed basin shapes and elevation ranges (López-Moreno et al, 2020)
The contributions of snowmelt dominate river runoff, and increased temperatures are widely recognized to result in changes in snow accumulation and seasonal runoff timing
Summary
Winter snowpacks typically represent the dominant component of warm-season streamflows (Cayan, 1996; Beniston, 1997; Barnett et al, 2005; Bales et al, 2006; Pomeroy et al, 2012). Changes in the timing of snowmelt are widely recognized as signs of a warming climate (Leith and Whitfield, 1998; Marks et al, 1998; Stone et al, 2002; Whitfield et al, 2002; Barnett et al, 2005; McCabe and Clark, 2005; Adam et al, 2009; López-Moreno et al, 2014; Rasouli et al, 2014), and how snow accumulation and snowmelt in mountain basins will respond to future climate change is a critical question. Vertical snow accumulation gradients in the mountains reflect orographic precipitation processes, time of year (Fitzharris, 1978) and redistribution by wind, vegetation and gravity (Ellis et al, 2010; MacDonald et al, 2010). Parsons and Castle (1959) suggested that the increasing snow water content with elevation could be represented as a “snow wedge” while Golding (1974) showed that snow depths in Marmot Creek were correlated with elevation and affected by slope, aspect, and vegetation
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