Data from the CSIRO shows there has been a huge fall in inflows across the Murray-Darling Basin in the past 20 years.
Lower rainfall translates to a big drop in water flowing into streams, rivers and dams across Australia’s largest river system.
Dr Francis Chiew, a research group leader in water resources assessment and prediction at the CSIRO, said long-term rain trends suggested a significant reduction in water availability in the Murray-Darling system.
He said his team applied a “general rule” when rainfall figures fell by 10 per cent.
“That tends to be accentuated or amplified as a 20-to-30 per cent reduction in (Murray-Darling basin) inflows,” Dr Chiew said.
“We are seeing something that is worse now.”
Dr Chiew said Murray-Darling communities need to think now about how they manage and value water.
“It is going to get worse,” he said.
“It means we need to squeeze more value out of water.
“It’s challenging but we need to appreciate water more and how to share it better.”
Modelling by the CSIRO shows annual basin inflows averaged 9,407 gigalitres per year from 1900 to 1999/2000.
In the 20 years since, average annual inflows to the system have almost halved, falling to 4,820 gigalitres.
The figures have irrigators worried.
“What we do know is inflows over the last 20 years compared to the wet decades of the last century have almost halved in every valley in the northern and the southern basin and this presents real challenges,” NSW Irrigators chief executive officer Claire Miller said.
Ms Miller concedes lower inflows will make management of the basin more difficult.
“Our challenge for all of our irrigators regardless of where they are, is how water policy and water management and reforms are going to try and even out what will be prolonged dry periods with probably more intense, larger, less frequent rain events,” she said.
The Murray-Darling Basin Plan has been widely criticised for not considering climate change, however the water framework that allocates water in the basin does take into account how much of the resource is available.
Over the past 20 years, water allocations have become more unreliable as inflows have fallen.
And as environmental water holders are the largest recipients, those allocations will experience the same ebbs and flows as irrigators face, depending on inflows each season.
It is something the Murray-Darling Basin Authority is monitoring.
“This climate reality is confronting and frightening – and raises questions about current water management arrangements – in particular, the basin plan,” Murray-Darling Basin Authority chairman Sir Angus Houston told the Murray-Darling Association conference at Wentworth recently.
“What we’ve been experiencing now goes beyond Australia’s normal climate variability (with) more frequent and severe droughts and extreme weather events,” he said.
Sir Angus told the conference climate change should not be viewed as a political issue.
“Rather it is a practical problem that demands practical action and policy so we can confront the challenge head-on,” he said.
“Climate change acts as a threat multiplier.”
Rice growers water dependent
The Australian rice-growing sector is one of the industries experiencing the effect of changes in water policy and increased variation of inflows.
Growers have gone from periods of reliably receiving water allocations for NSW general security licences in the Murray Valley to years now of low or no water allocations due to dry catchments.
“It just sort of fell off a cliff face,” rice grower and chair of the National Irrigators Council, Jeremy Morton, told the ABC’s Victorian Country Hour.
“If someone had said to me that we would have four years of zero allocation in a 13-year period 20 years ago, I’d have said you’re stark raving mad,” she said.
Ms Morton said allocations had gone from “a situation where we basically had water coming out of our ears” to a supply that was “a lot different” now.
Due to lack of water, last year’s rice crop was only 47,000 tonnes, while this year it is expected to nudge 450,000 tonnes.
Mr Morton argues the management of the system is exacerbating the effects of climate change on inflows and the rice industry.
“We know the climate of the basin is changing and rainfall patterns are shifting,” Sir Angus said.
“In the past 20 years there have been six to seven droughts.
“In this way, climate change can exacerbate existing vulnerabilities and have a destabilising effect, even in stable and wealthy nations like ours.”