Hot temperatures in the South Island are causing snow to melt earlier than usual, researchers say.

The "massive melt-off" could affect New Zealand's ability to generate hydro power for electricity supplies and affect irrigation and agriculture for farmers who are already feeling the pinch this summer.

University of Otago geography department associate professor Dr Nicolas Cullen. Photo / Supplied
University of Otago geography department associate professor Dr Nicolas Cullen. Photo / Supplied

A University of Otago research team has returned from one of New Zealand's largest but least known ice fields, the Gardens of Eden and Allah, in the South Island, with fresh concerns about the current heat's effects on glaciers and ice fields.

The retreat of the glaciers and seasonal snow is expected to affect water availability.

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The Gardens of Eden and Allah straddles the Southern Alps and feeds into Canterbury tributaries, the Rakaia and Rangitata, as well as the Whanganui on the west coast.

Episodes of hot weather similar to the one we are experiencing now are causing "considerable changes" that pointed to a "concerning future", said Otago geography department associate professor Dr Nicolas Cullen and Dr Pascal Sirguey of the university's surveying school.

"What we're seeing from these current high temperatures is a massive melt-off of snow. This snow usually provides a protective layer above ice fields and glaciers that reflects energy from the sun," Sirguey said.

Dr Pascal Sirguey of the University of Otago surveying school. Photo / Supplied
Dr Pascal Sirguey of the University of Otago surveying school. Photo / Supplied

"Glaciers are in retreat and that is definitely linked to climate change. Air temperature is a governing factor in the health of ice fields and glaciers as it controls melt and whether it rains or snows," Cullen said.

Snow melting earlier than usual is significant because snow and glacial ice are major reservoirs in the hydro-electricity cycle, Cullen said.

"Glacial and ice fields can provide up to 25 per cent of the hydro discharge."

Observations on the ground suggested the amount that has already melted is what you would normally see at the end of summer, Cullen said.

"It's not until March will we get a handle of things."

The group is involved in a project for Deep South, funded by the Brian Mason Trust.

The aim of the project is to make projections about how runoff from New Zealand's glaciers and seasonal snow will change into the future.

"I'm just one of a number of scientists that are interested to improve projections of snow melt in the alpine regions."

Improved water projections are essential for the development of climate change adaptation policies that can balance both the financial and intrinsic value of water, Cullen said.

Changes in the timing and volume of run-off from glaciers and seasonal snow would affect hydro generation, irrigation and agriculture.

"While rain provides the main input to our river catchments, once the snow has melted glaciers help to sustain water flow to our rivers. Water availability is set to become a major issue."

During drought years, glaciers and ice fields could be important for farms which sourced water from glacial catchments.

"For some people the glacial contribution could be important."

Sirguey and Cullen are investigating ways to gain clearer data on ice field changes by harnessing the latest satellite technology and modelling to get a bird's eye view from space to measure changes in the Gardens of Eden and Allah ice field.

There is urgency to determine evolving processes in the alpine areas.