Foretelling a storm

Traditional forecasting techniques to predict a storm, and storm a pa.

Written by       Illustrated by John Fellows

John Fellows

For thousands of years, people have been looking at the sky to predict the weather. A collection of Māori traditional knowledge, Anticipating Local Weather and Climate Outcomes Using Māori Environmental Indicators, by Darren King and colleagues, was published by NIWA in 2005. It explores traditional Māori forecasting techniques, based on short-term and seasonal observations, such as that early flowering and seeding of plants in spring may indicate the onset of a La Niña pattern likely to last throughout the summer, and that it’s possible to predict the arrival of a storm front by listening to the sound of waves crashing on a beach.

The latter effect is caused by gales around a deep low over the ocean that create waves of different length. Those of the longest wavelength travel faster than short waves, and if the low is travelling slowly, the long waves get ahead of it and can arrive a day or so before the worst of the weather, thundering on the beach with a characteristic sound. Long waves can also make kelp sway underwater in a charac­teristic way, and are felt by fish, such as cod, which swallow stones to become less buoyant and better able to hug the sea-floor when the larger swells arrive.

Historian James Cowan once recorded how Māori in Canterbury could foretell the approach of a southerly wind by the way the northwest arch cloud, formed by high-level winds crossing the Southern Alps, began to dissipate on its southern end. They could also distinguish between the approach of a south­erly bringing rain, and a dry southerly where the showers visible over South Canterbury would move away over the ocean to the east and not reach Christchurch.

He also told a story about a heavy snowfall in the Mackenzie Basin when several Pākehā musterers died. They would not follow the advice of their Māori companion, who recog­nised from the type of clouds, the lack of wind and the relative warmth as rain began that heavy snow was likely to follow.

Some of the best examples of weather forecasting occur in the history of warfare, where detailed accounts of the sequence of events and key decisions by leaders often survive.

In 1832, Te Rauparaha took a large war party from the North Island to besiege the Ngāi Tahu pa at Kaiapoi, near where Christchurch is today. The pa had strong natural defences, as it was surrounded on three sides by deep swamp. On the fourth side, a heavy wooden palisade protected it.

Realising that the defenders were well stocked with food and capable of withstanding a long siege, Te Rauparaha attempted to burn his way in. Three deep trenches were dug towards the palisade, zigzagged and roofed over to prevent the defenders firing their muskets down the length of the trenches. Once the trenches reached the pa, Te Rauparaha’s warriors threw bundles of mānuka against the palisade under cover of darkness, while the Ngāi Tahu defenders pushed them away.

After the arrival of reinforcements, Te Rauparaha’s warriors were able to pile up mānuka faster than the defenders could cope with. Then the attackers chanted karakia to bring a wind from the south that would blow the flames into the palisade while, inside the pa, karakia were chanted for a wind from the opposite direction.

Soon, a wind from the northwest began to blow. Ngāi Tahu knew that a wind from this direction is usually followed by a wind from the southwest so they fired the mānuka in desperation, hoping to burn it out before the wind changed.

As the fire took hold, Te Rauparaha urged his warriors forward to push the burning mānuka against the palisade. This exposed them to musket shot and some 25 of his men were killed before the wind changed to the south and the palisade was destroyed. Then the attacking force entered the pa, killing hundreds and taking many prisoners.

The use of fire by a besieging force against wooden defences has probably occurred thousands of times throughout history. The Venerable Bede in his Ecclesiastical History of the English People, written around 731, records an example. He describes an attack in 651 by Penda, the pagan king of Mercia, on a strong­hold of the Christian king Oswin at Bamburgh. Built on a steep-sided granite outcrop on the coast of Northumbria, Bamburgh had wooden walls on its landward side.

Penda’s soldiers demolished houses in nearby villages, gathering timber, wattle and thatch to stack against Bamburgh’s walls. Once the wind was blowing towards the fortress, they set fire to the fuel. Smoke rose so high in the air that it was seen by Bishop Aidan, who was in retreat on Farne Island three kilometres away. Aidan prayed to God for help and the wind changed, blowing fire and smoke into the attacking army. Some soldiers were injured and fear spread among others to see the power of God turned against them, and the siege was abandoned.

The NIWA study is based on Māori knowledge of how the weather has behaved in the past. A disturbing observation by some of the elders interviewed is that the old patterns are breaking down as the world’s climate warms, and observing the early flowering of plants does not work for seasonal forecasting as it once did.

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