Climate change close to home
26 March 2006
By RUTH LAUGESEN

Evidence is growing that New Zealand's climate is changing in line with global warming predictions. Research by the National Institute of Water and Atmospheric Research (Niwa) has found the west of New Zealand is generally becoming wetter and the east is getting drier.

Top New Zealand and overseas experts are to meet in Wellington this week for a conference on climate change, organised by Victoria University. British Prime Minister Tony Blair is to address the conference by video link on Wednesday.

This week, parliament is to debate Greens co-leader Jeanette Fitzsimons' private members bill that would allow local authorities to consider climate change when considering resource consents. That would mean, for example, considering the effect on climate change of a resource consent for a coal-powered power plant.

Climate change forecasts predict that over the coming century, westerly air flows over New Zealand will strengthen, leading to more rain in the west and less in the east. That would mean agriculture in the east, including Canterbury, would suffer from more frequent severe droughts. In the west, erosion and flooding would become more frequent, affecting farming and expensive infrastructure such as roads and bridges.

Potential pluses include faster-growing crop and grass growth in many areas because of warmer weather and higher carbon dioxide concentrations in the air. But invasive warm weather pests are also expected to become more of a problem.

Niwa meteorologist Georgina Griffiths studied rainfall gauge data between 1930 and 2004, which showed mean rainfall on the west of both islands had increased. The trend was strongest in South Island areas, where mean rainfall had increased between 10% and 20% since 1930. On the west coast of the North Island, the area between Wellington and Wanganui and north of Taumarunui showed no significant change in rainfall. In the New Plymouth and Taumarunui areas, mean rainfall had increased between 5% and 20%.

On the east coast of the North Island, mean rainfall varied between no significant change at some locations to a 25% decrease. On the east coast of the South Island, mean rainfall varied between no change and a 15% decrease.

Dr David Wratt, head of Niwa's National Climate Centre, said the findings were significant. "This is what's predicted in the climate models, so it suggests things are changing in the direction we expect," he said. Was it also possible that the changes in rainfall were part of normal climate variability?

"We can't be absolutely sure, because the climate does vary for various reasons. While it's reasonably straightforward to attribute changes at the global level or over large regions to climate change, it does get more difficult when you get down to small areas like New Zealand."