Winds over the southern hemisphere

Mean atmospheric pressure, 1971–2000

Mean annual sunshine hours, 1971–2000

Temperature variations, 1900–2004

The difference between climate and weather

The term ‘climate’ refers to long-term weather patterns, including:

• theaverage weather (such as monthly mean wind speed, and annual mean rainfall)
• thevariability of these conditions (such as frequency of frosts, floods, or tropical cyclones).

In contrast, the term ‘weather’ means the specific atmospheric events at a particular time. As Mark Twain wrote in 1887, ‘Climate lasts all the time and weather only a few days’¹

A temperate climate

As a small land mass surrounded by oceans, New Zealand enjoys a temperate maritime climate. Mean annual temperatures range from 10°C in the south to 16°C in the north. The coldest month is usually July, and the warmest is January or February.

Sunshine hours are relatively high in areas that are sheltered from the rain-bearing westerlies. Most of New Zealand has at least 1,800 hours annually.

Rain and snow

Most areas have between 600 and 1,600 millimetres of rainfall, spread throughout the year, with a dry period during the summer. Over the northern and central areas of New Zealand, there is more rain in winter than in summer. But for much of the southern region, winter is the driest season.

Snow falls mostly in the mountain areas. It rarely falls on the North Island coasts, or western parts of the South Island. The east and south of the South Island often have some snow in winter. Frosts can occur anywhere (although rarely in Northland and Auckland), and usually form on cold nights with clear skies and little wind.

What creates New Zealand’s climate?

The three key factors determining New Zealand’s climate are the prevailing winds, the surrounding oceans, and the country’s mountain ranges.

The wind and the oceans

The wind and oceans are affected by a global system of circulation. Heat or excess energy from the sun reaches the tropics every day and is then carried by wind and ocean currents to the cold, energy-deficient polar regions.

Westerly winds and the mountain ranges

Lying in the middle latitudes of the Southern Hemisphere, New Zealand is buffeted by strong winds coming from the west, known as the roaring forties and furious fifties. These dominate the circulation of atmosphere.

Travelling low-pressure systems, known as cyclones or depressions, develop in these winds as they head towards New Zealand. When they pass across or south of the country they bring rain and stormy weather. On reaching the barrier of the mountain chains they rise, dropping rain on the west coasts – especially in the South Island.

Lighter winds and anticyclones

Just north of New Zealand, near latitude 30° south, there is a belt of high pressure and lighter winds, where anticyclones bring fine weather. Occasionally, a tropical cyclone approaches from the South-west Pacific, resulting in severe wind gusts and heavy rain.

Climate change

In line with measurements worldwide, New Zealand temperatures rose substantially during the 20th century, increasing by about 0.7°C between 1920 and 2000. The warmest year (up to 2003) was 1998, closely followed by 1999. Climate change has produced other effects: fewer frosts, retreating glaciers and snowlines in the South Island, reduced alpine snow mass, and a rise in sea level of 14–17 centimetres.