Extending end-of-summer-snowlines for the Southern Alps glaciers of New Zealand back to 1949

New Zealand has a more than four-decade long (1977-2019) continuous record of measurements of the altitude of end-of-summer-snowlines (EOSS). These are obtained from oblique aerial photography during annual flights over the Southern Alps for a set of 50 'index glaciers' (EOSSALPS). Average EOSSALPS is 1842 m for the 1977-2016 period. Estimates for EOSSALPS are extended from 1977 back to 1949 by using observations from New Zealand's largest glacier, the Tasman (EOSSTAS). When EOSSTAS are not available, significant regression relationships are established with air temperature, regional climate indices and hemispheric scale climate teleconnections. This analysis involves glacier year values of annual mean Hokitika temperature, the Southern Annular Mode (SAM), the El Nino/Southern Oscillation Index (ENSO) and the Interdecadal Pacific Oscillation (IPO). Results show that over the seven decades there have been significant increases in EOSSALPS, and anthropogenic temperature increases play a significant role as found for Hokitika temperature. From 1949 to 1955 EOSSALPS varied little, but then rose to 1980. Thereafter, until 2010, annual EOSSALPS stayed about the same level with small fluctuations. However, from 2010 to 2019 it rose by a further 200 m above normal. The overall increase in EOSSALPS since 1949 is most significant, averaging +42 m per decade, or a total of 300 m. The length of the two monitored fast flowing Franz Josef and Fox glaciers over the same time are mimicked well by EOSSALPS with a four-year lag.

Automated summary

New Zealand has been continuously measuring the altitude of end-of-summer snowlines for over four decades, showing a significant increase in recent decades. EOSSALPS is not only related to temperature, but also influenced by regional climate indices and hemispheric scale climate teleconnections.