By Rich Bowden:

A new climatic index developed by Australian and Chinese researchers will help scientists understand why southwestern Western Australia has experienced such a decline in rainfall over the past 40 years.

The Southwest Australian Circulation Index (SWACI) — introduced by CSIRO statistician Dr Yun Li and climate physicists Professor Jianping Li and Juan Feng from the Chinese Academy of Sciences — points to a “…weakening of a major atmospheric circulation over the Indian Ocean,” as the cause of the lack of consistent rainfall, according to a CSIRO news release.

Since the mid-1970s south-west Western Australia has seen a 15-20 per cent decrease in average winter rainfall, from 323 mm in 1925-1976  to 276 mm from 1976-2003, said the CSIRO statement, adding the new index would help measure the weakening of the system.

“Using this new index we have found that the Southwest Australian Circulation is becoming weaker early in the winter wet season (May to July) causing the drier conditions observed in south-west WA,” Dr Li said.

Similar to the Southern Oscillation Index (SOI) which gauges the strength of the El Nino weather pattern in the Pacific Ocean and its effect on eastern Australia, the SWACI will assist meteorologists predict the strength of the index through seasonal winds over south Western Australia.

“The SWACI will help identify rainfall patterns throughout the year as well as long-term drying trends for south-west WA. It will also help increase the accuracy of global circulation models in predicting future climate scenarios,” Dr Li said.

The findings were presented by the team in the Journal of Climate.

Tags: chinese academy of sciences, circulation index, Climate, CSIRO, meteorology, weather western australia