Meltwater Runoff and Storage Based on Dielectric Properties of the Supraglacial Snowpack on Haig Glacier, Canadian Rocky Mountains.

Abstract:

Meltwater refreezing and storage in the supraglacial snowpack can reduce and delay meltwater runoff on temperate alpine glaciers, but models of glacier runoff that are used to examine mass balance and glacier water resources do not generally account for this storage. Past studies on Haig Glacier in the Canadian Rocky Mountains show a consistent over-estimate of the amount of summer runoff from the glacier, based on modeled melt vs. measured discharge. We hypothesized that much of the 'missing runoff' was associated with overnight refreezing of meltwater that is ponded on the glacier surface and stored in pore space of the seasonal snowpack. Additional energy is required to melt this refrozen water each day, such that a large fraction of the meltwater that is generated on the glacier is 'recycled' water.

To test this idea, we measured the temperature and meltwater content in the upper 40 cm of the supraglacial snowpack of Haig Glacier in spring and summer 2015. Thermistors and TDR probes were installed at 10-cm intervals at two sites in the glacier accumulation area. A Denoth meter was used to make point measurements for comparison with the TDR inferences of snowpack dielectric properties. These data are supplemented by automatic weather station data, used to calculate surface melt rates, and discharge measurements in the glacier outlet stream. We observed a strong diurnal cycle in snow water content, with the snowpack drying out overnight, but contrary to what we expected, there was negligible subsurface meltwater refreezing during our study. Overnight refreezing was restricted to a thin surface layer of the snowpack, while overnight drying was likely due to meltwater drainage to the snow-ice interface. We use our observations to calibrate and test a model of meltwater runoff from the glacier from summer 2015.