Regional Geography of Glacier Mass Balance Variability Over Seven Decades 1946–2015

Roger J Braithwaite,Philip D Hughes

doi:10.3389/feart.2020.00302

Abstract

Despite much progress with remote sensing, on–site measurements of glacier mass balance (with stakes and snow pits) still have advantages for resolution of interannual and seasonal changes of mass balance. Understanding these changes may help to identify the types of glaciers most sensitive to climate change. The standard deviation of mass balance data series for a few years describes the interannual variability, and balance amplitude, defined as half the difference between winter and summer balances, describes the seasonal variability. Interannual variability increases with seasonal variability, and seasonal variability increases with annual precipitation and summer temperature available from a half–degree gridded climatology. Measured glaciers have higher mean and median precipitation than average for all glaciers in the Randolph Glacier Inventory (version 6). High balance amplitudes are associated with warm/wet (maritime) environments and low amplitudes with cold/dry (continental) environments, as shown in previous studies of climate at the equilibrium line altitude. Balance amplitude can be modelled for half–degree grid squares in the glacier inventory using multiple regression of measured balance amplitude on the climate data. The resulting modelled balance amplitude is relatively low for Arctic Islands and Central Asia, but high for Western North America, Iceland, Scandinavia, Alps and Caucasus.

Highlights

Glacier mass balance study is concerned with changes in glacier mass, especially changes from year to year (Paterson, 1994; Cogley et al, 2011)
In Ahlmann’s method, field-workers mark measurement sites with stakes drilled into the glacier surface layer, measure changes in ice and snow surfaces relative to the tops of the stakes and measure the changing density of snow in snow pits dug close to the stakes or in snow samples taken by corers
We propose a simple theory for the correlation between balance amplitude and interannual variability of annual balance and test it with a much larger data set than available for previous exercises (Braithwaite, 1982; Braithwaite and Zhang, 1999b; Braithwaite, 2005)

Summary

INTRODUCTION

Glacier mass balance study is concerned with changes in glacier mass, especially changes from year to year (Paterson, 1994; Cogley et al, 2011). This is another example of the “high intercept” problem from the section “Seasonal Variability of Mass Balance and Annual Precipitation” as the regression curve passes well above most of the points for Arctic Islands and Central Asia at low and medium temperatures. For 173 glaciers with >4 years record, the multiple correlation r2 is only 0.57, which is not very impressive for predictive purposes, but the data set for 28 glaciers with >29 years record gives an impressively high r2 = 0.81 The latter data set avoids the “low intercept” problem as the regression line passes through the data points with the lowest measured balance amplitude (see discussion in Supplementary Material). If it were possible to reinterpret the 1961– 2016 changes of Zemp et al (2019) in terms of mass balance response to climate change (in m w.e. a−1 K−1), we would expect our high-amplitude regions (Iceland, Scandinavia, Central Europe, Caucasus and New Zealand) to show a high mass balance sensitivity

CONCLUSION

Findings

DATA AVAILABILITY STATEMENT