A century-long context for South Cascade Glacier mass balance

In order to accurately predict the changes in glacier mass balance that will occur under a

changing climate, the ability to couple detailed models of the atmosphere with glacier

mass balance models is of great importance. The mass balance time series measured on

South Cascade Glacier (SCG) for the years 1959-2003 has been modeled using a

physically based surface energy balance model driven by the RegCM, regional climate

model output with NCEP/NCAR reanalysis data as a boundary condition. We further

extend the SCG mass balance record to the beginning of the 20th century by driving our

model with data derived from the CRU TS2.1 gridded surface climatology. Physical

parameters used in the surface energy balance model were tuned to best replicate the

measured time series of mass balance components. The RegCM net balance result

correlates with measurement with r = 0.75. Performance for the winter and summer

balance components is poorer with r = 0.74 and r = 0.50. Performance using the CRU

data set is slightly better with respective correlations of 0.78, 0.72, 0.55. Our year 1902

onward results show that the greatest rates of mass loss occurred early in the century.

This rapid ablation is accompanied by low winter balance, and warm summer

temperatures. Retreat over the past decade has been accompanied by moderate to high

winter precipitation underscoring the importance of temperature in the current mass loss.

The noted recent decoupling between Pacific Ocean conditions and SCG mass balance is

replicated in our simulations; however, the earlier record of mass balance has shown

similar behavior. The tightest coupling between oceanic conditions and South Cascade

Glacier was in the middle part of the 20th century.