Abstract
This report details the current state of knowledge in developing an estimate of glacier ice volume (measured in water equivalents km3) for New Zealand. The work undertaken in this report is a significant step to better understanding the South Island glacier responses to climate forcing. This is the first time that the calculation of glacier ice volume has been undertaken from data obtained from the end of summer snowline surveys. A working group was established by National Institute of Water and Atmospheric Research (NIWA) to develop a methodology to establishing annual glacier volume changes through the Southern Alps. Much of the raw data used in this report originates from the 1978 New Zealand Glacier Inventory and the annual New Zealand Glacier Snowline Survey conducted since. Annual values of South Island glacier ice volumes have been calculated for the eight years 1993/94 to 2000/01, using 1992/93 as the base year. Since the 1992/93 glacier year, ice volumes have fluctuated from a minimum of 53.3km3 of water equivalent in 1993 to a maximum of 59.3 km3 in 1996/97 after a series of cooler years with largely west to southwest circulation. Subsequently, temperatures have increased, leading to stabilization or loss of ice volume. The annual regression linking ice area and volume for the Index Glaciers is consistent with seasonal climate patterns. Glacier volumes also have shown a strong correlation to interseasonal and decadal climate patterns of atmospheric circulation. Based on the results of this study and other work, the net gain of glacial volumes pre-1997 is likely to decrease. Two out of the last four years have shown a net decrease in glacier volume, whilst three of these have shown an increase in the equilibrium line altitude (ELA) for the glacier year. Located somewhere near the middle of a glacier the end-of-summer snowline indicates an equilibrium line where snowfall exactly equals snow loss over the past glacial year. An increase in ELA indicates a decrease in glacier snow mass.