Contributions of avalanches to glacier mass balance at the global scale

On-glacier avalanches contribute to non-linear mass balance patterns and, by channeling snow from upper headwalls onto the glacier surface, can maintain glaciers at low elevations despite increasing temperatures. Here we combine a gravitational snow redistribution model estimating avalanching with the Open Global Glacier Model (OGGM) to quantify the current and future contribution of avalanches to glacier mass balance for all mountain glaciers in the world. The avalanche contribution is added as a multiplicative correction factor of solid precipitation per elevation band, and the resulting mass balance is calibrated against global-scale geodetic data based on DEM differencing. The avalanche model is evaluated against a set of remote sensing observations at various spatial scales, including flux inversions and avalanche deposit outlines from Sentinel-1, and the influence of avalanches is quantified using ensemble simulations with CMIP6 climate data until 2100.

The model results show that avalanches can contribute substantially to glacier mass balance, with a strong spatial variability between glaciers and regions. The region most affected is New Zealand, with 19% of the total snow accumulation originating from avalanches on average. At the glacier scale, this avalanche contribution shows a strong variability that depends on glacier area and slope. Some glaciers more than double their snow accumulation while others lose mass by avalanching, and accounting for this contribution leads to more local variability in the mass balance gradients. We find that, at the regional scale and for many individual glaciers, accounting for avalanching has little impact on the simulated future evolution of glacier volume. This is because the effect of avalanching is already implicitly taken into account in the calibration against glacier-specific geodetic mass balance. However, for individual glaciers, explicitly accounting for the effect of avalanches can substantially impact the projected evolution. This is especially relevant for small glaciers at low elevations that, in the model simulations, may survive several decades longer than they would otherwise. We also find indications that removal of snow by avalanching may lead to a higher sensitivity to warming, and therefore faster thinning of steep glaciers at high elevation.