Updated inventory of glacier ice in New Zealand based on 2016 satellite imagery

The only complete inventory of New Zealand glaciers was based on aerial photography starting in 1978. While there have been partial updates using 2002 and 2009 satellite data, most glaciers are still represented by the 1978 outlines in contemporary global glacier databases. The objective of this project is to establish an updated glacier inventory for New Zealand. We have used Landsat 8 OLI satellite imagery from February and March 2016 for delineating clean glaciers using a semi-automatic band ratio method and debris-covered glaciers using a maximum likelihood classification. The outlines have been checked against Sentinel-2 MSI data, which have a higher resolution. Manual post processing was necessary due to misclassifications (e.g. lakes, clouds), mapping in shadowed areas, and combining the clean and debris-covered parts into single glaciers. New Zealand glaciers cover an area of 794 +/- 34 km(2) in 2016 with a debris-covered area of 10%. Of the 2918 glaciers, seven glaciers are >10 km(2) while 71% is 40%. Only 15 glaciers are located on the North Island. For a selection of glaciers, we were able to calculate the area reduction between the 1978 and 2016 inventories.

Automated summary

The study updated the glacier inventory of New Zealand using Landsat 8 OLI satellite imagery, finding a total of 2918 glaciers in 2016 with 10% of the area covered by debris. Among them, only 7 glaciers were larger than 10 square kilometers, while the majority of glaciers covered 40% of the area. The total area of New Zealand glaciers was calculated to be 794 +/- 34 square kilometers.