Glacier Mass Balance Prediction
NORTH CASCADE GLACIER CLIMATE PROJECT
Mauri S. Pelto, Director NCGCP
Nichols College, Dudley, MA 01571 Peltoms@nichols.edu
Glacier Mass Balance Basics North American Glacier Mass Balance Glacier Mass Balance Prediction Glacier Mass Balance Forecasting Global Glacier Mass Balance North Cascades Glacier Mass Balance
What is mass balance? Can we predict mass balance from climate data? Crucial to the survival of a glacier is its mass balance, the difference between accumulation and ablation (melting and sublimation). Climate change may cause variations in both temperature and snowfall, causing changes in mass balance. Changes in mass balance control a glacier's long term behavior. It is the most sensitive climate indicator on a glacier.  A glacier with a sustained negative balance is out of equilibrium and will retreat. A glacier with a sustained positive balance is out of equilibrium and will advance.

 Annual balance is the most sensitive annual  glacier climate indicator.  This sensitivity to climate indicates that climate variables should be useful in predicting mass balance.  Several models have been developed for the region, based on data from just a single glacier, South Cascade Glacier.   The models have tended to have substantial area, particularly in years with high positive or negative annual balances.  In this case with data from ten glaciers, we have a chance to build a robust model.     We utilized a range of variables from a range of sites, selecting the most accurate from these tests.  We have found that we can reasonably calculate mass balance from climate records for the mean of all the glaciers, but not for individual glaciers., with input from Snotel sites and Diablo Dam weather station.  North Cascade glaciers annual balance has averaged -0.54 m/a of water equivalent from 1984-2006, a cumulative loss of over 12.4 m in glacier thickness or  20-40 % of their total volume since 1984 due to negative mass balances. The trend in mass balance is becoming more negative which is fueling more glacier retreat and thinning.  We have also developed a mass balance forecasting method.

Mass balance data set   A Paper on this subject has been published in the premiere issue of The Cryosphere, A European Geophysical Union Journal


 

MODELED VERSUS MEASURED ANNUAL BALANCE

            NCGCP now has a long enough annual balance record to be contrasted meaningfully with climate data and climate indices.  The two key climate parameters are ablation season temperature and accumulation season precipitation.  We examined ablation season temperature for five regional weather stations and for two different month combinations (May-September and June-September) and found the Diablo Dam record for June-September to provide the best correlation.  For accumulation season precipitation annual balance was correlated with precipitation at Diablo Dam and Concrete WA for differing combinations of months and with April 1 SWE at five USDA SNOTEL stations.  The best correlation was with April 1 SWE.  In Figure 3 and 4 annual balance is plotted against ablation season temperature (May-September) at Diablo Dam and April 1 SWE respectively.  The resulting linear regression equations were then simply combined to calculate annual balance.  The resulting equation requires as input only the mean June-September temperature at Diablo Dam (t) and the mean April 1 SWE (s) at the SNOTEL stations.

(1)  ba= (2.5243s - 3.158)  + (-0.772t + 12.016)


This is the ablation season input data that was used to determine the linear regression equation that best fits climate data to mass balance 

This is the accumulation season input data that was used to determine the linear regression equation that best fits climate data to mass balance    

Above is the measured versus calculated annual balance for North Cascade glaciers.  The deviation between the points and the line represents the error in calculated annual balance.  Below is the annual relationship between measured and predicted.  The predicted annual balance yields generally more negative annual balances.