Why so wet?

Counterpoint aired an interview with hydro-climatologist Prof Stewart Franks this week and asked him to explain why it has been so wet.

It appears it is all to do with ENSO*, and once again proves the interconnectedness of all things.

In some years, around Xmas time, the fisherman in Peru have a bumper catch of anchovies.’Ole!’ they say as they feast, ‘Praise to El Nino – the Christ Child (literally ‘the boy’). Pass the patatas bravas, will you?’

Normally, the current along the South American coast Is from South to North, bringing cold water to the equatorial regions. This is known as La Nina – the girl. As a consequence, the ocean temperature is normally 8 degrees colder in the Eastern Pacific (South America) than it is in the Central (Tahiti) or Western Pacific (Austalia).

Sometimes, this cold current slows or ceases, and the water around Peru warms so that it is similar to the temperature in Tahiti. Hooray, more anchovies. This phenomenon (loss of the normal cold current) is the celebrated ‘El Nino’.

Whether El Nino will occur depends on lots of things that we can’t calculate, but by May each year the die is cast, and we can predict whether El Nino or La Nina will arrive at Christmas time.

Meanwhile……The climate in South East Queensland and Northern NSW (known as the ‘Greater Alstonville Area’) is characterized by summer rain.

During La Nina, the water near Tahiti is much warmer than Peru, the air pressure in Tahiti is high, and the breezes blow across the sea towards Australia, picking up moisture as they cross the ocean. Greater Alstonville is at risk of flooding rains – but generally the increased rainfall makes farmers and frogs much happier. (our Peruvian friends will have to choose a different tapas – maybe that ripoff stuffed olive one)

During El Nino, the water near Tahiti is as warm as Peru, and the air pressure in Tahiti is lower than usual, and the winds tend to flow easterly, towards Tahiti. The Greater Alstonville area does not receive the usual moisture bearing ocean winds, and the generous rain they bring. If El Nino dominates for a few years, we have a dry and sunburnt land.

* ENSO stands for El Nino Southern Osciallation. The Southern Oscillation Index is the difference in atmospheric pressure between Darwin and Tahiti. The effect was described by Sir Gilbert Walker, Director-General of British observatories in India early last century – so it has been known about for quite a while. It is low during El Nino and high during La Nina.

So, should we buy shares in Drizabone?

The Bureau of Meterology reports that La Ninas affect on the weather this year is weakening, as it usually does after summer.

In Autumn we’ll know more about what to expect next summer.

The BOM site has a much more detailed description of El Nino, La NIna and the SOI.



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