Observed surface snowmelt at high elevation in the Southern Alps of New Zealand

Abstract

Snowmelt is measured over a 34 day summer period at 2440m a.s.l. on Tasman Glacier (>500m above the equilibrium-line altitude) using a tipping-bucket lysimeter and an array of ten ablation stakes. A degree-day factor for snowmelt is calculated using a linear relationship between combined measured melt and the number of degree-days. The slope of the regression line for these data points provides an estimate of the degree-day factor for use in runoff models. Average snowmelt is 17.8 mm d-1, but varies between 0 and 78 mm d-1. Melt occurs in a series of distinct cyclical events or pulses, each of which lasts 5-8 days. These correspond to the eastward passage of anticyclones, then troughs over the Southern Alps. When all days with northwest airflow across the Southern Alps are excluded, the melt factor is 3.4 mm °C-1 d-1. Northwest days belong to a different population with a much higher average melt factor of 9.1 mm °C-1 d-1, but more measurements are required to better understand key processes.