Mass balance of Svalbard glaciers

We are investigating the mass balance of glaciers in Northwest Spitsbergen, Svalbard through the development, calibration and validation of a high resolution (200 m) spatially distributed surface mass balance model. Melt and runoff is calculated using a physically based surface and subsurface energy balance model. The model is forced using the European Center for Medium Range Weather Forecasts ERA reanalyses, which are validated against in situ meteorological records from Northwest Spitsbergen and corrected for systematic bias using a quantile-mapping technique.

We have also applied a calibration technique not previously employed in glacial modelling, notably 'multi-objective optimisation' designed to identify multiple optimal parameter sets that fit different characteristics of the real-world observations, enabling an assessment of the uncertainty associated with predictions. The model is first calibrated and validated for two 'benchmark' glaciers in Northwest Spitsbergen: Midre Lovénbreen and Kongsvegen, which have two of the longest continuous mass balance records in the Arctic (1968-present for Midre Lovénbreen and 1987-present for Kongsvegen) and have contrasting geometries.

The model is then applied to the entire northwest region of Spitsbergen (14,500km²) to investigate the interactions between glaciers, climate and topography at the regional scale. Overall, the regional modelling results exhibit surface thickening over high elevation interior regions and mass wastage around low-lying coastal margins, with an areally-averaged net mass loss of -0.20 ±0:19 m w.e. a^-1 between 1958-2002.

We have recently simplified the model to use a degree day scheme for calculating the surface runoff and are projecting the mass balance calculations into the future using output from various climate models and the IPCC Representative Concentration Pathway scenarios for the 21st century. Projections suggest that surface thinning over Northwest Spitsbergen will accelerate under most scenarios of anthropogenic climate warming, leading to substantial reductions in glacier area and volume.

Publications

Papers stemming from this project so far:

• Rye, C.J., Willis, I.C., Arnold, N.S. and Kohler, J., 2012. On the need for automated multiobjective optimization and uncertainty estimation of glacier mass balance models. Journal of Geophysical Research: Earth Surface, v. 117. doi:10.1029/2011JF002184.
• Rye, C.J., Arnold, N.S., Willis, I.C. and Kohler, J., 2010. Modeling the surface mass balance of a high Arctic glacier using the ERA-40 reanalysis. J GEOPHYS RES-EARTH, v. 115. doi:10.1029/2009JF001364.

The islands of Svalbard: Spitsbergen, Nordaustlandet, Edgeøya and Barentsøya. Our work focuses on glaciers in the vicinity of the Ny-Ålesund research base in Northwest Spitsbergen.

Plots of different sources of error between modelled mass balance and observed mass balance for multiple model runs for different combinations of model parameters for Midre Lovénbreen. Each dot represents a different model run. The 3 error measures are: i) area averaged cumulative error; ii) mean absolute error at individual stake locations; iii) mean absolute error in the mass balance gradient. The 'best' (optimal) solutions are shown as bold points. The single 'best' (compromise) solution is indicated by the red dot. From Rye et al, 2010.

Modelled area-averaged cumulative net mass balance for each member of the optimal set of model runs for Midre Lovénbreen. The red line denotes the compromise solution, while the solid blue line represents the observations and the dashed blue lines show the estimated error bounds (±2 SD). From Rye et al, 2010.

Modelled Northwest Spitsbergen net surface mass balance averaged over the period of the ERA-40 reanalysis (1958-2001). This run used the same parameter set as that which produced the compromise solution when three measures of error were compared for both Midre Lovénbreen and Kongsvegen combined.

Identifying different global climate models with which to drive a simplified mass balance model for NW Spitsbergen for the 21^st century. Output from seven climate models, each with three warming scenarios (represented by the IPCC RCP 2.6, 4.5 and 8.5) were investigated. Five out of the 21 were chosen to represent a range from cold and dry to warm and wet as indicated.

Annual gridded mass balance for decadal time slices: 2015-2025, 2040-2050, 2065-2075, 2090-2100 (moving from left to right) for Northwest Spitsbergen driven by the envelope of scenarios from the 5 climate models. The shrinkage of glacier area can clearly be seen, particularly by 2090-2100 (right column) and especially for the warm and dry (top row) and warmest and wet (bottom row) scenario.