Science News: The Big Dry
Step off a plane almost anywhere in Australia, and one of the first things you'll notice is water—or rather, the absence of it. In every public bathroom in Melbourne, signs remind people to be sparing with the faucet. In Brisbane, short showers are required by law. And throughout southern Australia, everyone using a toilet is supposed to choose the alternate-flush option.
Australia is locked in a drought of drastic proportions. In recent years, rivers have reached record lows. Temperatures have spiked to record highs. Cities are running out of water. Wildfires are burning. Ecosystems are suffering. And climate models are projecting more of the same—and worse—for many years to come.
The Australian continent has experienced dry spells since ancient times, but the length and severity of the current crisis have surprised even the most weathered climate experts. Australia's population has grown rapidly in recent decades, and there just isn't enough water to go around anymore.
"This is probably the worst drought that's been experienced in Australia since colonization by Europeans," says Hamish McGowan, a climatologist at the University of Queensland in Brisbane. "All of a sudden, the desert has come to town."
As climate experts struggle to apportion blame between natural cycles and human activities, technology-minded researchers are looking for innovative ways to keep Australia's taps flowing. Their struggle may provide important lessons for the rest of a warming globe.
"What has shocked Australia is that we've been managing our dams and water-allocation systems as if ... it would keep on raining," says Mike Young, professor of water economics and management at the University of Adelaide. "We haven't prepared ourselves for a massive [climate] shift
The Big Dry, as Australians have taken to calling it, has hit three parts of the country especially hard. The southwestern corner of Australia around Perth, the state of Victoria in the continent's southeast corner, and the area around Brisbane on the east coast have seen 15 to 20 percent declines in precipitation over the past decade or so, says David Jones, head of climate analysis at the Australian Bureau of Meteorology's National Climate Centre in Melbourne.
What's more, every 10 percent decline in precipitation leads to a 30 to 40 percent decline in the amount of water that runs off land into streams and rivers, Jones says. The runoff recession has greatly reduced the amount of usable water ending up in catchments, reservoirs, and dammed lakes.
The Murray-Darling River Basin—Australia's agricultural heartland—is an area of particular concern. Stretching across southeastern Australia from Brisbane to Adelaide, the million square kilometers of the basin make up just 14 percent of the country's area but account for 70 percent of its water use for crop irrigation.
Also called Australia's food bowl, the Murray-Darling River Basin produces some 40 percent of the nation's agricultural products, including grapes, cotton, rice, and dairy. Two million people live within the basin, and another million on the outskirts depend on it for drinking water, especially during dry times.
The region's water supplies are rapidly becoming less dependable, however. By the end of August this year, the amount of water stored in the basin's reservoirs and lakes was about 2,000 gigaliters (Gl)-21 percent of capacity, according to a government report. A year earlier, stored volume was 3,610 Gl, while historically, stored volume at the end of August has averaged 6,690 Gl, or 71 percent of capacity.
Even though rainfall has been up in recent months, the 2006-2007 growing season was the basin's driest in the 116 years for which records exist, according to an August 2007 report by the Murray-Darling Basin Commission. Computer models that predict weather patterns give a 75 percent chance that storage levels will remain low through May. "The system is really running on empty," Young says. "We're now borrowing water from the future."
Yet the future is not looking very wet either. Rainfall in Australia will drop by as much as 10 percent by 2030 and up to as much as 30 percent by 2070, according to predictions released this month by the Australian Bureau of Meteorology and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), a government agency headquartered in Canberra. And a report from the United Nations' Intergovernmental Panel on Climate Change (IPCC) in February predicted that by 2050, annual river flows in the Murray-Darling Basin are likely to fall by between 10 percent and 25 percent from their current depleted amounts. As early as 2020, the relatively stagnant water in the basin is expected to become too salty to be safe for drinking and irrigation. "Even if we get fabulous rains this spring and summer," Jones says, "it's only going to make a token of a difference."
It's likely to get hotter as well as drier, says climate scientist Neville Nichols of Monash University in Melbourne. Australia's average annual temperature has risen 0.7°C since 1950, according to a recent IPCC report. Recent drought years have all set record-high temperatures, Nichols adds. And temperatures over the continent are expected to rise between 1° and 5°C by 2070, depending on the extent of the world's increase in greenhouse-gas emissions, according to the recent CSIRO report.
With so much persistent dry heat, bushfires are on the rise throughout Australia. Massive wildfires during 2 of the past 5 years have burned about one-third of forests in Victoria. Besides killing trees and wildlife, these burns leave a litter of downed logs that can clog dams and rivers when rains do come. "It's sort of a biblical script at times," Jones says. "We have a drought followed by severe bushfires followed by severe floods. That kind of compounding is going to happen increasingly under global warming."
Why so dry?
Disentangling the numerous factors contributing to Australia's extended drought is difficult for a continent that has experienced dry spells for a long time.
Over the past few million years, dry times have alternated with wet times in Australia. During glacial periods that last for hundreds of thousands of years, the continent tends to be dry. Shorter interglacial periods, like the one Earth is in now, are relatively wet because less water is tied up in ice.
"The scary thing ... is that [Australia is] much dryer during this interglacial period than during the last interglacial period," says Gregory Webb, a geologist at the Queensland University of Technology in Brisbane.
On top of those long-term trends, every 4 to 7 years, Australia also experiences dry spells that typically last 12 to 18 months. Each such episode is driven by an El Niño, the periodic but irregular warming of tropical waters in the eastern and central Pacific Ocean. Cooling of the same waters is called a La Niña. "Australia has a climate that is heavily driven by El Niño and La Niña cycles," says Andy Pitman, codirector of the Climate Change Research Centre at the University of New South Wales in Sydney.
In a phenomenon known as the El Niño–Southern Oscillation, changing ocean temperatures alter atmospheric-circulation patterns and influence the weather on both sides of the Pacific Ocean. El Niños typically make Peru and Ecuador much wetter than normal, while leaving Australia hot and dry.
On average, an El Niño brings drought to eastern Australia 5 out every 20 years, Pitman says, allowing affected regions to recover between dry times. Over the past 25 years, however, repeated, strong El Niños have dominated the Pacific. Some measurements indicate that a La Niña will return this year, bringing much-needed rain, but it's impossible to tell how many more could follow. Whether global climate warming bears the blame for the recent surge in El Niños is a question that scientists haven't yet settled.
Still, no discussion of Australia's water crisis can neglect the possible influence of global warming. "There is very strong consensus among nearly all [global-climate] models saying that if you increase greenhouse gases, you get the decline in rainfall [in Australia] that we've seen over the last 10 to 30 years," says Nichols.
Human activity of another kind, land clearing, may also have exacerbated the drying trend in eastern Australia. In an upcoming Geophysical Research Letters, climatologist McGowan presents results from climate models suggesting that clear-cutting for agriculture has led to a measurable rise in temperature, a drop in rainfall, and a reduction in soil moisture in several parts of Australia—notably the Murray-Darling Basin.
The principle is simple, McGowan says. If you stand under a tree on a sunny day, the air feels cool and humid. If you walk into a clearing, you encounter a dryer, hotter microclimate. "You can imagine what happens if you clear hundreds of thousands of hectares," he says. "We are starting to see now that human activity is having a quantifiable effect on the severity of drought."
However, the picture is murky and confusing, experts say, and the nuances are too confusing to allow simple conclusions.
Twenty-one million people live in Australia. Nearly 90 percent of them live on the coasts, and most are concentrated in the nation's five largest cities—Sydney, Melbourne, Adelaide, Brisbane, and Perth. Nationwide, the population has increased by nearly 25 percent since 1990, and cities have been growing rapidly. Drought now affects the daily lives of most Australians.
Rules govern water use throughout the dry zones. Brisbane, Australia's third-largest city with 1.8 million people, has some of the country's toughest rules. Lawns can be watered only for a few hours every other day, and only with a tap-filled bucket or can. Forget about the drive-through car wash: Residents can scrub only their vehicles' windows, mirrors, and essential working parts. Four-minute showers are recommended to avoid fines for exceeding an 800-liter-per-day limit for each household. The average American single-family household, by the way, uses 1,325 liters—350 gallons—of water a day.
People aren't the only ones feeling the heat. Wildlife appears to be suffering too. That's extreme news, considering that much of Australia's fauna has evolved to cope with long dry spells.
A pregnant kangaroo, for example, can delay the birth of her young for months in case drought strikes. And many of Australia's birds and mammals extract all the moisture they need from leaves. Adaptations such as these have allowed animals to survive dry times and bounce back quickly when wetter weather returns. Now, however, development has drastically reduced the population sizes and habitat buffers that helped animals survive droughts in the past.
Koalas are in big trouble in some areas because drought is killing off several species of eucalyptus trees, the animals' main food source. Koala ecologist Alistair Melzer of the Central Queensland University in Rockhampton recently conducted an informal survey of a well-studied population of koalas in central Queensland. As many as 50 animals per square kilometer used to show up in similar searches. This time, Melzer found signs of koalas but no actual koalas. Throughout the region, he says, property owners have increasingly reported dead and disappearing koalas over the past decade. As eucalyptus forests change, Melzer says, other animals that rely on those trees will suffer, too, including a wide range of possum species.
To predict how animals and ecosystems will—or will not—cope with an increasingly dry future, scientists are looking deep into the past. About 45,000 years ago, for example, 90 percent of Australia's large mammals disappeared, including carnivorous, 200-kilogram kangaroos, marsupial lions, and flightless birds that weighed more than a ton.
Some evidence connects this rapid, continentwide megafauna extinction with the arrival of humans on the continent (SN: 1/20/07, p. 38), but scientists have also proposed that a major drought might have caused the die-off. In the Australian Journal of Earth Sciences last year, and in several papers soon to be published, geologist Webb and his colleague Gilbert Price of the University of Queensland report their studies of an area of southeast Queensland called the Kings Creek catchment. Their data show a long, gradual decline of both large and small animals, with no signs of hunting. Moreover, the extinctions coincided with a transition from lush forests to dry grasslands. "We interpret this to mean that aridification caused extinction," Webb says, acknowledging that the conclusion is controversial.
Figuring out such scenarios could help scientists find ways to avert the same catastrophes in the future. Pitman cautions, though, that "you've got to be very, very careful what you blame on global warming" or other human-caused phenomena. Crying wolf, he says, could be a disastrous way to undermine efforts to convince policymakers that human-induced global warming is real.
As scientists sort through the possible causes of Australia's water woes, governments at all levels—from federal to local—are taking action. In Perth, a desalination plant is already turning seawater into drinking water—but using lots of energy to do it. Making major financial investments in an uncertain future, Melbourne and Sydney are planning their own desalination plants. In Queensland, communities are beginning to build wastewater-recycling plants, but that idea has sparked some strong opposition.
At the same time, sophisticated water markets are developing to allow farmers, businesses, and others to buy, sell, and trade access to the precious liquid. "If you want a larger share, you have to buy it," Young says. "The price of water is going up enormously."
Australians are rising to the challenge of living with less water, but they continue to grapple with an environment that they don't recognize any more. "We really will run out of water if it doesn't start raining," Webb says. "It's spooky.