Otago's climate

One of Otago's glories

For many, the character of Otago lies in the glories of its landscape and its climate:

• the western snow-capped, forested mountains
• the pristine southern lakes
• the extensive dry tussock grassland ranges and valleys with their summer heat and winter cold
• the mighty rain-fed Clutha River slicing through the land
• the horticultural valley niches
• the busy grassy coastal landscapes

The landscapes and the climate are in a constant tug of war - the landscape dictating the climate's field of play, the climate weathering away and creating Otago's special environment.

Storms and floods

The succession of weather systems (highs and lows) brings periods of good weather and bad, with no rain to excessive rain. Winds from the south bring cold weather and snowfalls in the winter that can smother sheep and damage power lines. Heavy warm rains from northwesterlies can overload rivers and rapidly melt alpine winter snows, causing floods in western lakes and rivers, such as occurred in Queenstown in January 1994, December 1995 and January 1999.

In the east of the region, persistent rainy easterlies can cause serious flooding of low-lying plains. This variability of the climate is perfectly natural, but the impacts can be made much worse by human activity such as building houses or altering the landscape in known floodplains.

Westerly winds and mountains in the way

At 45°S in the oceanic southern hemisphere, Otago lies in a zone of strong moist westerly winds. Within this zone it experiences a succession of depressions (lows) and subtropical anticyclones (highs) that bring alternating periods of rainy and sunny weather. But the Southern Alps, rising to 3026m at Mt Aspiring, provide a solid barrier to the flow of these weather systems, diverting them around the South Island and wringing out their moisture, making the mountains wet and the interior basins dry.

Milford Sound's annual mean rainfall of 6813 mm contrasts sharply with Alexandra's 346 mm, barely 130 km away. Enough rainfall spills over the Divide, however, to provide considerable snow and rain water in the headwaters of Otago's catchments, to fill its major lakes and rivers. The lower mountain ranges in the south and east of the region play a similar obstruction role for southerly and easterly winds.

Hot summers and cold winters

The climates of locations near the coast are moderated by being near the ocean where temperatures don't change so much, and by the fluctuations of winds and weather from the sea. Coastal Otago therefore tends to have a fairly cloudy maritime climate with a relatively small swing in temperature from summer to winter.

But further inland, the cloud is less, the oceans no longer hold much sway, and the climate is more continental. There, the summer days are hotter and the winter days colder, with much colder nights. The lowest temperature officially recorded in New Zealand was minus 21.6 °C at Ophir in Central Otago, on 3 July 1995.

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