Understanding what causes droughts and floods

By July 19th, 2011

The latest research into how variations in the atmosphere and oceans combine to produce impacts like the major droughts and floods experienced recently in south-eastern Australia will be presented today in Canberra at a science workshop hosted by the South Eastern Australian Climate Initiative (SEACI).

SEACI is a three-year, $9 million research program investigating the causes and impacts of climate variability and change across south-eastern Australia.

SEACI Program Director David Post said the one-day workshop will focus on the implications of SEACI research for water resource planning and management.

“Water managers have faced a diverse set of challenges in recent years, ranging from the most persistent rainfall deficit of the instrumental record in the ‘Millennium Drought’ of 1997-2009, to one of the strongest La Nina events on record with widespread rainfall and flooding across Australia in 2010–2011,” Dr Post said.

“While 2010 brought welcome rains for much of south-eastern Australia, there is growing evidence from SEACI research that a long-term trend towards a drier climate is taking place.

“We now also have a better understanding of the drivers behind these variations in rainfall, as measured by things such as: the El Nino-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Southern Annual Mode (SAM) and the sub-tropical ridge (STR). We also have some understanding of how the drivers of rainfall interact to produce extreme climatic events such as the Millennium Drought and 2010/11 floods.

“The next step is to determine to what extent some of the changes we have seen so far are linked to global warming, and to figure out how these conditions may change into the future in a warmer world.”

“As SEACI unravels the mysteries of the interactions between the drivers of climate in south-eastern Australia, there can be greater confidence in predicting future climatic conditions.”

Dr David Post, SEACI Program Director

SEACI research has already determined a relationship between rainfall in south-eastern Australia and the intensity of the STR. The STR is the belt of high-pressure systems around the mid-latitudes.  It is the surface signature of the Hadley Cell, which is the process by which heat is transported from equatorial zones to mid-latitudes. There are changes in the Hadley Cell, and therefore the STR, associated with global warming, with the STR intensifying with increasing global surface temperature.

“However, there are other climatic relationships which are not yet known,” Dr Post said.

“For example, while it appears that the IOD and SAM may trend more positive with increasing global temperatures, it is not clear how ENSO will respond to increasing global temperatures.

“As SEACI unravels the mysteries of the interactions between the drivers of climate in south-eastern Australia, there can be greater confidence in predicting future climatic conditions. This will assist resource managers and users to adapt to climate change.

“South-eastern Australia is facing a future climate which will likely be characterised by longer droughts, so SEACI will provide water managers and policy makers with improved seasonal forecasts and longer term climate projections to better plan for the future.”

SEACI is a partnership between the CSIRO Water for a Healthy Country Flagship, the Bureau of Meteorology, the Murray–Darling Basin Authority, the Victorian Department of Sustainability and Environment, and the Australian Government’s Department of Climate Change and Energy Efficiency.

The science workshop is being held at the Shine Dome, Canberra, from 9am on Tuesday 19 July and will feature SEACI researchers discussing key highlights from the 2010/11 SEACI research.

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