Friday, June 13, 2014

Indian Ocean Dipole set to triple frequency of floods, bushfires and droughts

Climate change and extreme weather is likely to hit the Indian Ocean rim countries much harder over the coming century. That is the conclusion of a new study lead by CSIRO climate scientist Wenju Cai.

The research lead by Wenju Cai from CSIRO's Marine and Atmosphere Division outlines that an increase in greenhouse gases and climate change is likely to cause more extreme positive Indian Ocean Dipole (IOD) events to occur and that this will likely triple the frequency of bushfires, floods and drought in Australia, Africa and India from one event every 17 years to one every 6 years.

The interaction between ENSO and IOD still needs much more research and study to understand. IOD events are often triggered by El Nino, but can also sometimes occur during La Nina years as well.

Dr Wenju Cai told the ABC:

"Most of our severe bushfires were preconditioned by the Indian Ocean Dipole... When a summer season is preceded by an [extreme positive] Indian Ocean Dipole our bushfires tend to be much more severe.

"Now this is in Australia, but it has global impact. [For example] in Indonesia, a positive Indian Ocean Dipole tends to cause drought. You may recall in 1997 we had a wild bushfire in Indonesia... emitting a lot of pollutants and smoke that caused health problems to many millions of people in the region and also cost lost economic activity because people couldn't go out because of the visibility problem.

"In the meantime, in eastern African countries, they experienced devastating floods, causing thousands to die... and displacement of many hundreds of thousands."

According to the Bureau of Meteorology in their 3 June 2014 report the Indian Ocean Dipole is currently in a neutral mode.
The Indian Ocean Dipole (IOD) is currently neutral. Model outlooks suggest the IOD is most likely to remain neutral through winter, with two of the five models surveyed suggesting a positive IOD may develop during spring. Positive IOD events often coincide with El Niño and are typically associated with large parts of southern and central Australia experiencing lower rainfall than usual.

The climate variability of the Indian ocean basin affects the lives of millions of people from Africa, the middle east, India, Indonesia to Australia. Past extreme positive IOD events in 1961, 1994 and 1997 lead "to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries" said the study authors. The study - Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming (abstract) - asserts that the likely impact of increased greenhouse gases will increase the frequency of extreme IOD events:

We find that a mean state change—with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean—facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.

Impact of Indian Ocean Dipole came to light in 2009

The importance of the Indian Ocean Dipole for rainfall and drought conditions for Australia was only recently discovered in 2009. A team lead by Dr Caroline Ummenhofer from the UNSW Climate Change Research Centre highlighted in a study - What causes southeast Australia's worst droughts? (abstract) - that some of Australia's most severe and longest droughts, including the Federation Drought (1895–1902) and World War II drought (1937–1945) and Millenial drought (1995-2010), are driven primarily by Indian Ocean variability, not Pacific Ocean conditions.

"The ramifications of drought for this region are dire, with acute water shortages for rural and metropolitan areas, record agricultural losses, the drying-out of two of Australia's major river systems and far-reaching ecosystem damage," said Dr Ummenhofer in 2009.

"We have shown that the state of the Indian Ocean is highly important for rainfall and droughts in south-east Australia. More than the variability associated with the El Nino/La Nina cycle in the Pacific Ocean, the Indian Ocean Dipole is the key factor for driving major south-east Australian droughts over the past 120 years.

A following paper by Cai, Cowan and Raupach (2009) discussed how the Indian Ocean Dipole reduced spring precipitation providing the precondition for more intense southeast Australian bushfires. The link was made with the devastating Black Saturday bushfires occurred in Victoria killing 173 people. Over half the significant bushfire seasons since 1950 were preceeded by a positive Indian Ocean Dipole event.

This new study on the Indian Ocean Dipole comes after the first Australian Government budget under the leadership of Tony Abbott slashed $116 million from the CSIRO research budget. Yesterday the CSIRO announced more than 30 jobs will be cut from their Marine and Atmospheric Research division reported the ABC, including eight in from the CSIRO Aspendale laboratory where Dr Cai is based. The Abbott Government also announced the abolition of the National Water a time when we need expert advice and management of water resources with drought conditions highly likely especially if a positive IOD develops for the Austral spring to accompany a strong or super El Nino by the end of the year.

This could be a wild ride and a hot and dry summer given Australia's government is hell bent in denying the impact of climate change.


  • Wenju Cai, Agus Santoso, Guojian Wang, Evan Weller, Lixin Wu, Karumuri Ashok, Yukio Masumoto & Toshio Yamagata (2014) Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming (abstract) Nature 510, 254–258 (12 June 2014) doi:10.1038/nature13327
  • Karen Palenzuela, ABC Environment, 12 June 2014 - Climate change set to triple drought, bushfires and floods in Australia
  • Ummenhofer, C. C., M. H. England, P. C. McIntosh, G. A. Meyers, M. J.
    Pook, J. S. Risbey, A. S. Gupta, and A. S. Taschetto (2009), What causes southeast Australia's worst droughts? (abstract), Geophys. Res. Lett., 36, L04706,
  • Cai, W., T. Cowan, and M. Raupach (2009) Positive Indian Ocean Dipole events precondition southeast Australia bushfires (abstract) GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L19710, doi:10.1029/2009GL039902, 2009
  • Lead image: Map of Australia and Indian Ocean showing Negative and positive phases. Source: Climate Change Research Centre, University of NSW - Indian Ocean causes Big Dry: drought mystery solved
  • Image: Graph of correlation between IOD and drought from David Walker, Executive Officer, LPLM - Indian Ocean Water temperatures impact on SE Australian rainfall