New research also questions the future viability of the Snowy Mountains scheme, built in the 1950s and 60s to divert water to grow irrigated crops in central NSW.

Long-term weather records reveal the once-mighty river, fed by melting snows and high seasonal rainfall, is one of Australia's earliest and largely unheeded climate change casualties.

Data published by CSIRO and the Bureau of Meteorology track a 70-year trend toward hotter, drier conditions across the Snowy catchment, stretching from the river's headwaters in Mt Kosciuszko National Park in NSW to the East Gippsland coast at Marlo in Victoria.

The records show a 40per cent loss of annual rainfall over the past 30 years, with a 20 to 40per cent drop in flows in five of the Snowy's main tributaries. An agreement to return 28per cent of natural flows by 2012, signed in 2000 by the Federal, NSW and Victorian governments ''may yet prove unachievable,'' according to research published by Monash University scientists.

The Rudd Government has committed $50million to return flows to the Snowy. Announcing the deal last year in Cooma, Climate Change and Water Minister Penny Wong said this would be achieved through a combination of water efficiency and licence buybacks.

But research led by Monash University geographer Peter Wheeler points to a continuing decline in rainfall across the region, which is predicted to cut the Snowy's natural flow by 35per cent within 20 years, and by 50per cent by 2070.

Mr Wheeler said meteorological records showed rainfall and water from snow melt across the catchment ''have been in deficit since the 1950s, basically from the time the Snowy Mountains scheme was being built.'' This drying trend is also affecting the Gippsland Lakes and other major rivers in the region.

''We're looking at a long-term trend of rainfall deficit, not a couple of years of drought,'' Mr Wheeler said.

Full coverage, analysis in today's Canberra Times