It works by participants volunteering the spare processing power on their computers to crunch weather data from a state-of-the-art global climate model, that includes a finely detailed regional model over Australia and New Zealand.
The results are returned automatically to the project although participants can opt to track progress as the model runs via an interactive graphic.
Dr Rosier said the computing power harnessed in this way from thousands of volunteers is phenomenal.
"It enables scientists to run these global and regional climate models many thousands of times - far more than would be possible with conventional computing resources," Dr Rosier said.
"That is what is needed when attempting to address problems involving extremely rare weather events and enables scientists to put some hard numbers on how the risks of these events might be changing."
For example, last year's drought was one of the most extreme of the past 70 years with almost 80 days without rain on average over the North Island - far more than recorded previously.
"Events like last summer's drought are rare but the frequency of them could be changing.
"Scientists want to find out how the risks of such events might be changing with human-induced climate change, and the Weather@home experiment enables us to do just that."
Flooding in Golden Bay and Nelson in December 2011 - and this month's floods in Christchurch - could also be better understood via Weather@home ANZ.
The launch also comes ahead of the upcoming release of the next sections of the Intergovernmental Panel on Climate Change (IPCC)'s latest report - the most comprehensive and up-to-date assessment of the world's vulnerabilities from climate change and options for reducing impacts.
The reports, out next month, will focus on risks and impact of climate change on a regional as well as global scale, including specific impacts in New Zealand, Australia and the Pacific, and options for limiting greenhouse gas emissions.
Weather@home ANZ was a collaboration among NIWA, the University of Oxford, the UK Met Office, the University of Melbourne and the University of Tasmania, with financial support from Microsoft Research.
It is part of the climateprediction.net project, based in Oxford, which has been running highly successfully for the past 10 years.
In the UK, participants are helping to discover whether this year's floods are linked to climate change.
The more people who participate, the more science can be done, Dr Rosier said.
Those keen to take part should go to weatherathome.net or climateprediction.net to register.
