Study to look at history of extreme climate events in Sydney

Thursday 6 October 2005

Researchers from the University of Newcastle have been awarded an Australian Research Council Linkage Project grant to investigate the history of droughts and floods in the Sydney Basin.

Dr Stewart Franks and Dr Russell Drysdale from the University of Newcastle will work with the Sydney Catchment Authority and researchers from the University of Melbourne and the Australian National University.

The research is in response to the ongoing debate on climate change and the recent crippling El Nino-related drought, which caused widespread social, environmental and economic hardship over most of eastern Australia, including severe reductions in Sydney's water supply levels.

"Most climate scientists agree that the recent El Nino event was one of the most severe on record," says hydroclimatologist Dr Stewart Franks. "Our research team believes that the best way to understand El Nino behaviour is to explore its long-term history."

"At present, much of what we know about El Nino is based on the instrumental climate record, which in eastern Australia only extends back to the 1800s. In terms of natural climate variability, 200 years is insufficient to capture the true variability of El Nino/Southern Oscillation (ENSO)."

"We will be targeting the last 1000 years in order to unravel the true relationship between ENSO, the Inter-decadal Pacific Oscillation and rainfall in eastern Australia, and will delve into the geological record and reconstruct climate information by 'proxy'".

Geoscientist Dr Russell Drysdale says that valuable information on past climate and environmental change can be extracted from caves and river deposits in the Sydney region.

"Cave stalagmites, which build up layer by layer from the cave floor, are extremely sensitive to climate variability, especially rainfall. The amount of drip water feeding them diminishes as rainfall decreases. This produces chemical changes that leave a distinctive signature in that particular stalagmite layer."

"Detailed study of a stalagmite's geochemistry may therefore reveal continuous variations in a region's rainfall patterns. Modern instrumental techniques and precision radiometric dating will allow us to identify the incidence, frequency and the magnitude of drought over many thousands of years," says Dr Drysdale.

A long-term monitoring study at Wombeyan Caves Reserve (100km southwest of Sydney) conducted by University of Newcastle PhD student Ms Janece McDonald, revealed the high level of sensitivity of the Wombeyan cave systems to the recent El Nino event. Actively forming stalagmites from these caves will be the major focal point for the drought history part of this study.

Sydney Basin flood history will be reconstructed from sediments contained in cores extracted from the Hawkesbury River floodplain. Changes in the physical and chemical properties of the sediment will allow the team to identify flood frequency. Dating of the sediments will provide the chronological information necessary for the team to piece together the timing and incidence of flood-rich and flood-poor epochs over the last millennium.

Ultimately, the information gathered on flood and drought occurrence will be used to improve the design and management of water resources systems to account for the full spectrum of climate variability that is encountered in the Sydney Water supply catchments.

For interviews: Dr Russell Drysdale on (02) 4921 5749.