Field‐calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap

Abstract

Understanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

Meltwater percolation, impermeable layer formation and runoff buffering on Devon Ice Cap, Canada

“…We calculate the summer (JJA) surface energy and mass balance of DIC high-elevation area using the model described and calibrated for DIC by Morris and others (2014), a version of which has also been applied to palaeo ice masses (Muschitiello and others, 2017). Broadly, the model consists of four modules: surface energy balance; SMB; subsurface percolation and refreezing and vertical temperature flux, operating on a 1-D fixed vertical 1 cm grid.…”

“…Our model was calibrated with field measurements of bulk density, snow water equivalent, and snow depth along the CryoSat Line (Fig. 1) by Morris and others (2014) to calculate the optimum values of fresh snow density, fresh snow albedo and bare ice albedo. For a fuller model description and details of the calibration procedure we direct the reader to Morris and others (2014).…”

“…1) by Morris and others (2014) to calculate the optimum values of fresh snow density, fresh snow albedo and bare ice albedo. For a fuller model description and details of the calibration procedure we direct the reader to Morris and others (2014). The details of the runs performed in this study are given in Table 1.…”

Enhanced ice sheet melting driven by volcanic eruptions during the last deglaciation

“…We apply a field-validated physically based one-dimensional energy balance model of melt, refreezing, and runoff processes that occur within a given snowpack/ice column 68 . The runoff model has previously been field validated for Devon Ice Cap, Nunavut, Canada, where it was shown to be capable of fully accounting for density, temperature, and albedo evolution of the snow/ice column 68 . It is able to account for feedbacks associated with melt, refreezing within the snowpack/ice and runoff, and therefore provides more physically realistic runoff estimates than simpler degree day models of surface mass balance.…”

“…The model uses hourly values of air temperature, cloud cover, precipitation, relative humidity, and incoming shortwave radiation flux (SWRF) that are interpolated to 15 min timesteps. A full description of the model is in Morris et al 68 , however a modification in this study is that we account for changes in cloudiness, whereas constant conditions were assumed previously.…”