Margins call: is Goyder’s Line still relevant?

Goyder’s Line has long formed the boundary between South Australia’s crop belt and its hotter arid parts. Is climate change pushing the line south? There’s no easy answer. Certainly, those living on its edges are getting a fast-tracked taste of a climate-changed landscape. Rachel Williamson talks to those on both sides of the line about what their future holds.

We’re bouncing up the hill behind Andrew Bretag’s 160-year-old home, through the gum trees, past the ewes that he jokes pay the mortgage on his 1,400-hectare farm, aiming for the million-dollar views at the top of the ridge.

We stop at the sandstone ruin known as Oakse’s hut. Above us is the slow whomp…whomp…whomp of the single wind turbine on Bretag’s property – another mortgage supporter, and part of the Hornsdale Wind Farm, which feeds Australia’s first big battery.

We hop out of the ute and immediately I spot it: there, in the distance to the east.

“You can see it really well this year because it’s been really dry – we’re well below our rainfall averages for this time of year,” Bretag says, tracing a line with his finger along the horizon where the cartoonish blue-green of wheat and canary-yellow of canola meet the golden grasslands beyond.

This is Goyder’s Line, a geographic phenomenon pencilled onto maps in 1865 to show the edges of where rain reliably falls in South Australia. Goyder’s Line starts hard up against the Victorian border a little north of Pinnaroo, 243 kilometres east of Adelaide. It curves up past Eudunda and Burra to Terowie before sweeping up between Yongala and Peterborough to form two peaks, one at Orroroo and the second at Mount Remarkable. The line descends southwards to Moonta and finishes with an almost-afterthought slash of a pencil to bisect the Eyre Peninsula up to Ceduna, nearly 800km to Adelaide’s north-west.

North and west of the line, rain is sparse and unreliable. To its south, precipitation averages 250 millimetres a year or better. This year and for who knows how long into the future, that boundary will be important: it’s mid-September and the area is several days into an unseasonal heatwave. After a sodden 2022, Bretag’s farm, Glenrest, has received just 45% of its average annual rain – and the dry season is already beckoning.

Andrew and Rhianna Bretag and their three children live just north of Jamestown, an agricultural hub three hours’ drive from Adelaide that more than a century ago was home to one Reginald Murray Williams – the original RM Williams. They are on the “right” side of the Goyder transition zone: a lush agricultural area where crops are (almost) guaranteed for eight out of every 10 years.

Theirs is the side dotted with big gum trees. As the land recedes down the ridge and into the distance, the trees become squat and sparse. Water is the key ingredient in this land.

Climate change is not a factor for the people who work this area – yet. Tentative predictions of permanently hotter, drier weather are yet to manifest. But the Bretags can see from their dusty, toy-strewn verandah the drylands nibbling at the edges of the northern and eastern boundaries.

Thirty kilometres up the road, Peterborough is already living the hotter, drier future.

“If we haven’t got water, we can’t exist,” says Ruth Whittle, the town’s mayor for the past 33 years. “We’re north of Goyder’s – we’re in the drier area, so not so many people crop anymore, and it’s getting worse. It’s getting drier, hotter.”

Peterborough is the counterpoint to Jamestown’s agriculture-focused industriousness. It’s tourist-town cute with ye-olde façades and part-time shopfronts filled with crafts. It’s worked hard to build a tourism industry from its railway heritage, which appears to be paying off as locals and tourists jostle for parking spots on a sweltering Friday morning.

It relies on water piped in from the Murray River, almost 200km away, along with its rainwater tanks. But it’s only a drought away from danger.

The two SA towns are a microcosm of our future. Whittle believes Peterborough is already living in a markedly changed climate; Jamestown can afford to kick the climate can down the road a little longer.

However, data is mounting that questions how much longer Australian farmers in these transition zones can continue to beat the odds. And while crops can run south, people and trees find it much more difficult to uproot.

Goyder’s Line

The 1850s was a boom time for South Australian agriculture. A period of unusually wet years, combined with a surge in demand for food as neighbouring Victoria caught gold fever, drove men and their families further and further north in the nascent colony, searching for new lands for pasture.

But in 1864 those settlers got their first taste of the region’s climatic whims. The great drought of 1864–66 exposed those who’d moved too far north, killing stock en masse and desiccating vegetation. Powerful dust storms skinned the land of topsoil.

With pastoralists crying out for rent relief, the government wanted to know the southern limit of the drought zones to define who got financial support, and who didn’t.

The fear is that Goyder’s Line is moving south. It’s a boundary based on climatic conditions, so if the climate changes, that boundary will change as well. Right?

Alone, on a horse, South Australia’s surveyor-general George Goyder traversed the state. With limited rainfall records to lean on, he spoke to graziers and took cues from where saltbush, mulga and mallee grew. The result was a thick line across the state, mapping the 250mm rainfall isohyet (the line that joins points with the same amount of precipitation): the distinguishing line between arid and semi-arid zones – and one of the most famous incarnations of climate as a defining edge.

Global warming creates both fear and fascination for climatic transition zones like Goyder’s Line. The fear is that the line is moving south. It’s a boundary based on climatic conditions, so it seems logical to assume that if the climate changes, that boundary will change as well. Right?

Around the world many such lines exist – and they’re on the move. Researchers suggested in 2018 that the 100^th Meridian in the US – the line notionally splitting the country between arid western grasslands and humid eastern plains – might be shifting east. But the researchers said global warming played only a minor role. In North Africa, the Sahara has been expanding at an alarming rate – based on rainfall, by about 10% between 1920 and 2013, with the starkest impact being Libya’s shift from mostly semi-desert to mostly desert over that time. One culprit is the “tropic squeeze”, a phenomenon where the wet tropics are getting narrower and the dry edges are expanding; over-grazing and poor land management are also to blame.

The tropic squeeze is having an impact on Australia’s own transition zones. In 2018, US and UK climate scientists used satellite imagery to show the edges of the tropics have been moving polewards at a rate of 44km a decade since 1979. Warmer global temperatures are energising the Hadley cell circulation system (see page 90), which means the hotter air at the equator rises higher and travels further towards the poles than it once did.

“This expansion has intensified the subtropical ridge over southern Australia, pushing cool season mid-latitude storm tracks further south, leading to a reduction in winter rainfall and runoff across the region,” wrote CSIRO researcher David Post, lead author on a 2014 study on what it will mean for water availability in Australia.

Projections from CSIRO’s Climate Change in Australia website forecast “with high confidence” that winter and spring rainfall in the Burra-Orroroo corner of Goyder’s Line will fall by as much as 15% by 2030, as seasonal storm systems move south.

So is Goyder’s Line shifting south? Well, it’s complicated.

Moving target

In a 2012 paper taking a look at the limits of SA’s grain-growing areas, CSIRO’s Uday Nidumolu and his co-authors traced a new line, which ran to the north of Goyder’s, based on a measurement of the ratio between rainfall (P) during the growing season (April–October) and potential evaporation (E) of 0.26. If the 1865 line is the limit of reliable rainfall, the researchers found that the 0.26 P:E isopleth (a line on a map connecting points at which a given variable has a specified constant value) is the dry margin, “hard edge” of the Australian grain belt.

“The surprisingly close fit of this ratio with much of the Australian grain belt suggests a climatically determined hard edge to the cropping zone,” they wrote. “If this finding is correct, it follows that a warming and drying trend will shift the 0.26 P:E isopleth and hence the edge of the grain belt towards the coast.”

But regions protected by hills, such as the area stretching from Burra right up to Mount Remarkable, and areas with microclimates and different soil types are likely to see smaller changes. In 2012, even the worst-case-scenario model predicted 2050 as the year that isopleth line reached the Goyder’s current position.

“There’s such significant natural year-to-year variability in rainfall, but also important decade-to-decade variability,” says co-author Peter Hayman, from the South Australian Research and Development Institute. “However, when you read the summary of climate models it seems to be that a warmer world is a wetter world, except in the mid-latitudes. So I tell my farmer friends this is likely true, except where you chose to buy or inherit a farm.

“In terms of rainfall I am increasingly comfortable in saying I don’t know.”

Back at the Bretag kitchen table, Andrew pulls out a green, hardcover exercise book containing the farm’s rainfall records dating back to 1868. We pore over them, noting his mother’s careful notes marking occasional snowfall and totting up some of the later years that had been missed in the maelstrom of farm life.

The numbers are weird: rainfall at Glenrest farm is trending upwards over time. I check the BOM data for Jamestown and it’s the same.

But the very last number in the book shows how changeable this land can be. An average year sees 432mm of rain. By 17 September 2023 – a day on which temperatures soared above 30°C very early in the long dry season – Glenrest had recorded only 197.5mm of rain since the start of the year.

The rainfall issue, then, is not how much – but when. And it’s not the only thing driving change along Goyder’s Line, and throughout Australia’s crop-growing regions.

Boom and bust

If sheep (and, for a lucky few, wind turbines) provide a farmer’s bread-and-butter income every year, when it rains wheat delivers the cream.

“Cropping is boom or bust,” says Martin Clark, who farms next door to the Bretags and has a reputation for an elephantine memory for weather.

“You get a frost or a dry year like this and your yield reduces. But we can go from an average of three tonnes of wheat per hectare to last year’s record of five and a half. It’s just phenomenal. Last year’s the biggest grain year I’ve ever seen in this country.”

---

Mind the gap

The wheat yield gap is the difference between what farmers are currently harvesting, and the amount that could be achieved using the best adapted crop varieties with the best land management practices. Calculations on CSIRO’s Yield Gap Australia website are based on 15 years of data (2000–14) – a period long enough to account for climate variability but short enough not to be greatly affected by technology and climate change. Data includes ABS crop production figures and crop simulation, weather and soil-type data.

Former CSIRO researcher and yield gap expert Zvi Hochman says the yield gap data is bad news .

Papers Hochman wrote in 2017 and 2021 show that water-limited wheat yield – how much it’s possible for farmers to grow given access to water, or lack of it – fell from 4.4 tonnes per hectare in 1990 to 3.2 tonnes in 2015.

The Yield Gap Australia website shows Jamestown’s average yield gap is 51%: farmers are getting an average of 2.4 tonnes per hectare, but their water-limited potential is 4.8 tonnes.

Hochman’s 2017 paper lays out the underlying numbers. Genetics delivers a 0.5% annual yield boost; extra carbon dioxide in the air adds another 4%. But lower autumn and winter rainfall accounts for 83% of the water-limited yield decline; higher temperatures prompt the other 17%: if a wheat plant’s florets (small flowers) form in temperatures over 30°C they’ll be sterile, and in 20–25°C temperatures plants mature too fast and grow fewer seeds.

To top it off, the WHO says high ozone levels, caused by hot ground-level temperatures, caused 2–5% of wheat crop loss in southern Australia last year.

---

Australia produced a record almost 40 million tonnes of wheat in 2022, according to the federal Department of Agriculture, Fisheries and Forestry. The grain is critical to the livelihoods of Aussie croppers. It’s the country’s biggest food export. Last year it was our seventh largest export good overall – just ahead of crude petroleum. Even though lentils are an up-and-comer and canola is pure money, wheat is the easiest to grow and hardiest.

“Whether Goyder’s Line has moved, I don’t know,” says Clark. “Weather’s a long game. If you came here spring this time last year and said, ‘Do you think it’s moved?’, well, what do you reckon? There’s bloody rain. We were getting a hundred mil a month for three and a half months.”

What Clark knows for sure is that he’s producing more with the same amount of rainfall, as a result of new moisture-conserving farm practices such as reduced tillage and improved soil and temperature monitoring.

Elsewhere in Australia, this isn’t true. Rainfall in cropping areas has fallen by 1% a year since 1990 and in the south-east, rainfall in the critical months of April and May is down 25%, says former CSIRO researcher Zvi Hochman – point-man on the country’s wheat yield gap (see “Mind the gap”, opposite).

Agronomist Darren Pech agrees that, so far, changing practices are doing more with less. Sitting in his Jamestown office, Pech tells me that moisture conservation measures – such as spraying summer weeds – which ease dependency on seasonal rainfall, are probably the biggest game changer.

It’s only 8.30am but through the window, the main road – RM Williams Way – is already shimmering in the heat.

“And there’s a thousand other things,” Pech adds. “Controlled traffic, where they’re driving on the same wheel tracks all the time to try and minimise soil compaction. A greater reliance on phosphate and nitrogen inputs. A big increase in weather stations with moisture and temperature probes.”

Those practices safeguard moisture gifted from summer storms, which used to be lost to evaporation or wind as farmers repeatedly tilled soil for weed control. Massive boom sprays, machines that punch individual holes in the ground to sow seeds and harvesters that follow GPS-set paths all preserve soil texture – a boon for Jamestown’s red clay soils, which only grudgingly give up moisture when dry or tightly compacted.

These innovations also change the soil microbiome, as more organic carbon in the ground gives microbes a better chance to tolerate heat.

Whether improved farming practices will be enough to overcome rising temperatures and all their complex affects, only time will tell. “Farmers are paddling harder and staying on the same spot,” Hochman says. “It’s not universally true, but nationally it’s true.

“Technology is enabling us to maintain actual yields on a steady keel and maybe even a slight increase, but we’re not seeing the dividends from all the technology improvements that we would see if the climate wasn’t squeezing us to the degree that it is.”

Across the line

The price Peterborough pays for its low rainfall is living on the financial margin. It’s a town where people do find it easy to uproot and move away.

Without a strong agricultural economy, the town’s heyday was in the 1950s, when as a railway hub for steam engines it supported 5,000 residents. Town elders even thought it was headed for big-city status, says Peterborough newsagent and historian Chris Woodman. They clearly forgot the cautionary tale of Lancelot, a neighbouring town that was in the running for the rail industry but missed out: by the 1930s all that was left of it was a cemetery and some building ruins.

Peterborough’s industry slowly eroded as rail switched to diesel engines; the last passenger train left its station in 1986. The population has dwindled to 1,600 people, half of whom are retirees or welfare beneficiaries, with a median income almost half the national average. State and federal grants make up as much of the Peterborough council budget as rates.

Mayor Ruth Whittle is open about the challenges those facts present. She’s lived through the town’s peak and its decline: she was born there, and has been mayor for the past 33 years. In her office, a stack of Australian flags and boxes of files line the back wall; the temperature is mercifully cool as heat begins to radiate off the pale sandstone buildings that line the main street.

“Our big thing now is tourism,” Whittle says, leaning back in her chair. “We’ve had to work hard at it. It was always there. People always wanted to see things, but we didn’t take too much notice of it. We didn’t have to. We had an industry and tourism didn’t matter.

“Then, suddenly, we didn’t have an industry.”

But Peterborough’s biggest worry is water. Bureau of Meteorology (BOM) records for the town go back to 1881 and the data shows rainfall is trending down.

“Everyone is worried about what happens on the eastern seaboard, as far as all the water that is going into cotton farms and all the other farming, because it means the water is not coming into the Murray River,” Whittle says. “We depend on Murray water. There are aquifers underneath us but they’re getting low.

“We belong to the Murray Darling Basin Commission – we’re stuck out here in the middle of nowhere, and yet we belong to a river commission! Which to me is always funny. We’ve got to try and fight the good fight all the time and keep that water coming down the Murray.”

Thus Whittle looks east. Farmers to the south look at their weather stations, and scientists gaze at satellite data and computer models. But the first signs of how climate change might affect transition zones could be underground, in the rainforest beneath our feet that a group of Swiss ecologists estimates contains 59% of all life on Earth.

The life subterranean

A thin skin of soil covers our planet. It’s home to a vast variety of organisms, from fungi to bacteria to plants, vertebrates and mammals that live underground. Earthworm excrement – castings – boost soil fertility and texture; fungi breaks down organic debris to make nutrients such as carbon, nitrogen and phosphorus available, as do bacteria. Soil viruses help with microbial evolution and population. Some, like fungi, are tailored to wetter soils. Others, like actinobacteria, are one of the first to jumpstart after a long dry.

This complex system is as vulnerable to booms and busts as crops, says Gupta Vadakattu, a senior researcher at CSIRO, as rainfall becomes more episodic between periods of hotter, drier weather.

“If you have a plant type, let’s say, that requires a microbial community to perform, and a changing climate changes that, then of course that vegetation will disappear from the native systems in different ways,” says Vadakattu. “One example would be most native systems plants are dependent upon what’s called mycorrhizal fungi, the bridge between soil and the roots that help moisture uptake and phosphorus and other nutrients.”

Harsh heatwaves, such as the September event I’m caught in, can be catastrophic for soil.

“A field study spanning 18 years found microbial efficiency was reduced at higher soil temperature, with decomposition of recalcitrant, complex substrates increasing by the end of the period along with a net loss of soil carbon,” wrote the multiple authors of “Scientists’ warning to humanity: micro-organisms and climate change”, published in 2019 in Nature Reviews Microbiology.

Forecasts for hotter, maybe drier futures are triggering new ideas on how to improve drought resilience or water-use efficiency in plants. One idea is transferring soil with dry-adapted microbial communities to locations without that same soil makeup, says Martin Breed from Flinders University, one of Australia’s top soil science authorities.

That might become a crucial frontline as researchers try to protect the increasing acreage of agricultural land that will be in semi-arid locations, like those on the dry side of Goyder’s Line.

“If you have a plant type that requires a microbial community to perform, and a changing climate changes that, then of course that vegetation will disappear.”

The morning I called Breed from a carpark in Morgan, SA, was already 10°C above the mean daily temperature for the month. From inside my increasingly oven-like car, I asked him about how heat-baking will affect soils in places like Jamestown and Peterborough.

“In these semi-arid transition communities there’s going to be all sorts of changes that we have not been measuring whatsoever where I would be absolutely certain that there would be species of microbes that are dropping off the post all the time,” he says.

“I imagine there’d be all sorts of microbial communities that, under drier or hotter conditions, will start protecting themselves [by] no longer producing the compounds, the molecules … that the plants and the animals would want.

“There’s bound to be ripple effects on the plants and animals in those systems.”

Is the world under our feet beginning to shift? We don’t know. We’re not sure, either, as to why the predicted march southward of plants and crops hasn’t happened yet.

Does the future hold more Peterboroughs and less Jamestowns? “We’ve been [running] the farm now seven years,” Andrew Bretag says. “It’s not really long enough for us to really know, to try to work out [changing] averages. In 20 years time we might have more of an idea.”

Peterborough mayor Ruth Whittle’s take on outback town survival is much simpler: no water, no life.