Lake Pukaki receives the highest snow-melt inflow of any
hydro lake in the South Island. Photo by Gerard O'Brien.
Irrigators, power companies and mountaineers could all be
affected if climate change leads to changes in snow levels.
New research from the National Institute of Water and
Atmospheric Research (Niwa) reveals that snow melting off the
Southern Alps has a greater impact on North Otago waterways
than anywhere else in the South Island.
An assessment of 20 years of daily temperature and
precipitation data from the Virtual Climate Station showed
that of the large rivers that reach the sea, the Waitaki had
the highest snow-melt contribution with 12%, while Lake
Pukaki had the highest snow-melt inflow of any South Island
hydro lake, with 18%.
Niwa hydrology scientist Dr Tim Kerr said the findings would
have important consequences for water management, and civil
''Increased flow from snow-melt in summer is beneficial for
irrigation, but decreased flow in winter, when snow builds
up, is problematic for hydro-electricity.''
Knowledge of how snow-melt might affect the size of a flood
was also an important consideration for building structures
near rivers, or when forecasting flood events, he said.
''Add into the mix the potential for climate warming to
change these seasonal and flooding effects as less snow and
more rain falls, and you can see that it is worth having an
idea where snow-melt is important.''
Overall, it is estimated 3.4%, or 1 litre in every 30, of the
South Island's river flow comes from snow-melt, and New
Zealand Mountain Safety Council alpine and avalanche
programme manager Andrew Hobman said that also meant trampers
and climbers should be wary of making river crossings.
''Rivers are definitely going to be up at the moment and they
are going to drop and rise throughout the day as that melt
''It's important to understand before you go on a tramp or
trek that you can get a significant change from crossing a
river in the morning, or at dawn, to when you are are coming
back again in late afternoon - that river might have risen
quite a lot through just daily melt.''
He said it was also important to be wary of avalanches, which
could be caused by snow-melt, and warned people to stay off
unsupported snow if they were trekking above the bush line.
He advised people to watch out for warning signs such as a
sudden end to vegetation, which could be in indicator they
were entering an avalanche zone, if they could see snow above
''It's a good time to remember that 55% of all fatalities are
climbers, and the majority of those fatalities occur in the