AUSTRALIA’S annual rainfall will increase by an average 8.4mm by 2099, according to results from computer models that have been brought under the one roof for the first time.

Two academics from the Australian National University, Michael Roderick and Wee Lo Lim, have crunched the numbers from 39 models run by organisations such as Australia’s CSIRO and its equivalents in France, Canada, Germany, Japan, the US and Britain to produce a downloadable book that shows all their predictions individually and averaged.

The book and e-book, An Atlas of the Global Water Cycle, will be launched today at the university.

Dr Roderick and Mr Lim calculated that, by 2099, Australia’s nationwide rainfall will have increased by an average of 8.4mm. But include an extra 11.2mm of evaporation across the country and the final result is a loss of 2.8mm.

Globally, rainfall is predicted to increase by an average of 46.9mm.

The Australian averages hide wider predicted regional variations. According to the data, by 2099, the Top End will be receiving 50-100mm more rain than the 1970-1999 average.

All of Victoria, and most of South Australia and Western Australia, will receive up to 50mm a year less than now.

Eastern Tasmania will receive up to 50mm less and the western half of the state will receive 50-100mm less.

One Japanese model predicts 149.7mm more rain by 2099 across Australia and one German model predicts 128.1mm less per year. Australia’s long-term, nationwide rainfall average is about 450mm a year.

Dr Roderick said the compilation of the data was an objective work. “There’s no interpretation,” he said. “This is straight out what they (the models) say.”

He said scientists did not (openly) put more stock in some models over others but “the science is being done at the moment” on which model made the best projections.

All 39 models predict more rainfall across the globe, over land and sea.

Dr Roderick said the information could be useful for people such as farmers and water engineers. “(This work) will allow people to see all the individual runs of models,” he said.

“Here you can see for yourself and people can download a digital copy for free.”