Monday, September 20, 2010

El Nino/La Nina

It is raining luscious rain here in south-east Queensland. Does this surprise anyone? Some people might say 'no'. But are we all so forgetful to lose sight of the extremely low dam levels we experienced only a couple of years ago where the government forced everyone to become extremely water efficient and the general drought conditions that we experienced here in Australia? No watering the garden, no washing the car, etc, etc.

In light of the cyclical patterns of these weather events I thought I would try and understand the El Nino/La Nino concept a little better. Having read only a few pages on the net, I can share the following.

  • it is a cyclical pattern
  • when the El Nino event is on the Australian side of the Pacific, the east coast of Australia experiences below average rainfall (drought-like conditions, depending how extreme this event is)
  • when a La Nina event is on the Australian side of the Pacific, east coast Australia will likely experience higher than average rainfall (as we currently are experiencing)
  • the concept relates to the oscillation of surface air pressure between the eastern and western sides of the Pacific (hence the 'southern oscillation index' (SOI))
  • The SOI measures the strength of this oscillation and measures the difference of surface air pressure between Tahiti and Darwin
  • If the SOI is positive it indicates a La Nina event (above +8), if it is the negative it is an El Nino (below -8).

Presently Australia is experiencing a positive SOI, with the Bureau of Meteorology currently reporting (13 September 2010) the 30-day SOI as +25. Thus the east coast of Australia is having conditions that would indicate a La Nina and we can expect to receive above average rainfall. Yeah!

Don't get complacent with the water saving measures though, despite our current wetter than usual conditions. We will eventually swing back to the El Nino event (on average every five years) and need all the water we have saved during La Ninas and also need to be well-practiced in how to scrimp on water. This is the time to perhaps install a rainwater tank (if you didn't when the government was basically giving them away) to collect water for your garden, hook up irrigation systems in your garden to either your water tank or your grey water system or just undertake some of the maintenance around your house that needs a little extra water now so that you don't cut into the water supply when we don't have much.

Don't forget water is a precious resource.

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