Firn layer impact on glacial runoff: a case study at Hofsjökull, Iceland

Abstract

Abstract:A mass balance-runoff model is applied to Hofsjökull, an 880 km 2 ice cap in Iceland, in order to assess the importance of the firn layer for glacial runoff. The model is forced by daily temperature and precipitation data from a nearby meteorological station. Water is routed through the glacier using a linear reservoir model assuming different storage constants for firn, snow and ice. The model is calibrated and validated using mass balance data and satellite-derived snow facies maps. Simulated mass balances and snowline retreats are generally in good agreement with observations. Modelled cumulative mass balance for the entire ice cap over the period 1987/1988 to 2003/2004 is 7Ð3 m, with uninterrupted negative mass balances since 1993/1994. Perturbing the model with a uniform temperature (C1 K) and precipitation (C10%) increase yields static mass balance sensitivities of 0Ð95 m a 1 and C0Ð23 m a 1 respectively. Removing the firn layer under otherwise likewise conditions results in almost unchanged total runoff volumes, but yields a redistribution of discharge within the year. Early summer discharge (June to mid August) is amplified by roughly 5-10%, whereas late-summer/autumn discharge (mid August to November) is reduced by 15-20% as a result of accelerated water flow through the glacial hydrological system. In comparison, applying a climate-model-based temperature and precipitation scenario for Iceland until 2050 results in higher runoff throughout the year, increasing total runoff by roughly one-third. The results emphasize the role of the firn layer in delaying water flow through glaciers, and the influence on discharge seasonality when firn areas shrink in response to climate-change-induced glacier wastage.

Inclusion of glacier processes for distributed hydrological modeling at basin scale with application to a watershed in Tianshan Mountains, northwest China

“…Each of these media has markedly different hydrological properties. In the accumulation area, the glacier ice is overlain by a firn layer often several tens of meters thick, whereas in the ablation area, bare ice is exposed to air when the winter snow has melted (de Woul et al, 2006). For the summer accumulation type glacier (Ageta and Higuchi, 1984), accumulation and ablation both take place during the warm season, and the formation of superimposed ice on this continentaltype glacier is important, while during the cold season, ice gain is not significant because of little snowfall (Fujita and Ageta, 2000;Xu et al, 2011).…”

Atmospheric flow indices, regional climate, and Glacier mass balance in the Canadian Rocky mountains

“…Summer and net balance residuals are scattered equally around the mean, and in all mass balance series the flow indices model exhibits the least deviation from zero. Lags in glacier response might be expected in the b s or b n series, as consecutive high melt summers would reduce the firn cover, leading to deceased albedo and increased melt totals (de Woul et al, 2006). However b w values reflect only the atmospheric conditions of the current winter -the observed autocorrelation is likely a product of the autocorrelation inherent in the PDO and the Z 500 time-series.…”

Near-Surface Temperature Lapse Rates over Arctic Glaciers and Their Implications for Temperature Downscaling

“…For large and complex regions like the Canadian high Arctic, running a regional climate model for multiple years at a resolution desirable for modeling glacier melt (;1 km) is computationally challenging, so statistical temperature downscaling remains an attractive proposition. The lapse rate used to downscale nearsurface temperatures is often taken to be the moist adiabatic lapse rate (MALR 5 68-78C km 21 ; Glover 1999; Flowers and Clarke 2002;Thomas et al 2003;Arnold et al 2006;Bassford et al 2006a,b;de Woul et al 2006;Otto-Bliesner et al 2006a;Raper and Braithwaite 2006). However, temperature lapse rates measured close to glacier surfaces can differ substantially from the MALR (Greuell and Bö hm 1998;Braun and Hock 2004;Hanna et al 2005;Marshall et al 2007).…”