Abstract
ABSTRACTAlbedo is an important parameter in the energy balance of bare-ice surfaces and modulates glacier melt rates. The prolongation of the ablation period enforces the albedo feedback and highlights the need for profound knowledge on impacts of bare-ice albedo on glacier mass balance. In this study, we assess the mass balance sensitivity of 12 Swiss glaciers with abundant long-term in-situ data on changes in bare-ice albedo. We use pixel-based bare-ice albedo derived from Landsat 8. A distributed mass-balance model is applied to the period 1997–2016 and experiments are performed to assess the impact of albedo changes on glacier mass balance. Our results indicate that glacier-wide mass-balance sensitivities to changes in bare-ice albedo correlate strongly with mean annual mass balances (r2= 0.81). Large alpine glaciers react more sensitively to bare-ice albedo changes due to their ablation areas being situated at lower elevations. We find average sensitivities of glacier-wide mass balance of −0.14 m w.e. a−1per 0.1 albedo decrease. Although this value is considerably smaller than sensitivity to air temperature change, we stress the importance of the enhanced albedo feedback that will be amplified due to atmospheric warming and a suspected darkening of glacier surface in the near future.
Highlights
Glaciers react to changing climatic conditions by losing or gaining mass
To analyse the effect of spatially explicit bare-ice albedo, we developed the following model setup: In a first model run, the spatially distributed observed snap-shot bare-ice albedo derived from Landsat 8 was implemented and applied whenever a grid cell became snow-free (Fig. 3a)
Based on spatially distributed snap-shot bare-ice albedo derived from Landsat 8 and a wealth of point mass-balance data from 12 Swiss glaciers, we assessed the mass-balance sensitivity to changes in bare-ice albedo over a time interval of two decades
Summary
Glaciers react to changing climatic conditions by losing or gaining mass. In recent years, global atmospheric warming enhanced glacier melts worldwide (Zemp and others, 2015). The strongest driver of mass balance on alpine glaciers is net shortwave radiation (e.g. Brock and others, 2000a; Klok and Oerlemans, 2004; Pellicciotti and others, 2008), mainly due to the fact that net longwave radiation is close to zero and the glacier surfaces are characterised by low albedo values in their ablation areas that are exposed over most of the summer season (Paul and others, 2008) This causes a strong, positive feedback that enhances surface melt significantly (Oerlemans and Hoogendoorn, 1989; Van de Wal and others, 1992; Paul and others, 2007) and shapes the spatial ablation pattern (Paul and others, 2005; Sugiyama and others, 2011; Naegeli and others, 2015). We aim at investigating the impact of knowledge on spatially distributed bare-ice albedo on glacier mass balance, separating it from the effect of potential changes in snow albedo
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