Understanding Climate Risk

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Archive for March 20th, 2011

The big wet Part 1

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In this long post I describe how climate change and variability have contributed to the big wet of the past year and outline a role for climate change that challenges the orthodox model of understanding how climate changes through trend analysis.

Last year was the second wettest year recorded in Australia since 1900. Deadly floods occurred in Queensland and a series of increasingly severe floods affected Victoria and New South Wales during spring and summer. There is no doubt the origin of the wet year was due to climate variability. The strongest La Niña on record with an SOI of 21.5 from Sep–Dec was the origin of the wet conditions.

  • Total Sep–Jan rainfall in eastern Australia was 602 mm second only to 1972–3, just beating 1974–5. Sep–Dec rainfall was 425 mm, the wettest on record.
  • The El Niño-Southern Oscillation (ENSO) Index averaged 21.5 over the Sep–Feb period; the strongest on record, producing very strong La Niña conditions.
  • The Indian Ocean Dipole (IOD) was negative between Aug–Oct 2010. A negative IOD is characterised by warmer than usual waters near Indonesia. The combination of a negative IOD and La Niña is rare and results in wetter than usual conditions across much of Australia (see http://www.bom.gov.au/climate/IOD/negative/).
  • Victoria recorded its wettest January at 119 mm and Sep–Jan at 532 mm.
  • Pan evaporation and diurnal temperature range over eastern Australia in 2010 were the lowest on record.

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Written by Roger Jones

March 20, 2011 at 4:32 pm