Most Australians have known drought in their lifetimes. Many have memories of cracked earth and empty streams, paddocks of dust and stories of city reservoirs with only a few weeks’ storage of water. However, new research finds that, over the last 1,000 years, Australia has suffered longer, larger and more severe droughts than those recorded over the last century.
These are called “megadroughts,” and they’re likely to occur again in coming decades. Megadroughts can last multiple decades. Sometimes they can last centuries with occasional wet years offering only a brief relief from the drought. Megadroughts can also occur during shorter periods of time under very extreme conditions.
Studies show that megadroughts have occurred several times across every inhabited continent over the last two millennia. They’ve dealt profound damage to agriculture and water supplies. They have caused an increase fire risk and, one can honestly say that they have even contributed to toppling civilizations.
Unless the full potential of Australian drought is included into the country’s planning, management and design, megadroughts will continue to impact on society. As a result, the environment will likely worsen in coming decades.
The role of climate change
Instrumental records only go back so far. In Australia, they cover only the last 120 years or so. Scientists can gauge local, yearly climate further back in time, by deciphering clues written in tree rings, corals, and buried ice (known as ice cores), among other archives. This information is vitally important to our understanding of past patterns related to megadroughts.
Historically, droughts have been defined by rainfall deficits, and these deficits can be largely attributed to complex interactions between oceans and the atmosphere over a long time. For example, decades-long La Niña conditions have been linked to droughts during the medieval era in both North and South America.
In contrast, current research suggests that human-caused climate change plays a more important role in amplifying drought conditions, as rising global temperatures continue to increase evaporation. Of course, there is some uncertainty in climate models about the effects of climate change on rainfall at local and regional scales. However, climate change is putting places that have previously endured megadroughts—such as Australia—at an increased risk of megadroughts in future. This can wreak havoc on the environment as one could well imagine.
Megadroughts and collapsing civilizations
Currently, there are part of the the United States – specifically Arizona, Nevada and Utah— that are in the throes of a megadrought. This one has lasted more than twenty years. Historically, megadroughts have profoundly impacted societies and environments. In the American southwest, megadroughts in the late 1200s most likely caused early peoples to desert the Mesa Verde cliff dwellings. Likewise, the Hohokam peoples relied heavily on a canal system, and this dependence in a time of severe and extended drought may have contributed to that civilization’s decline during the 14th and 15th centuries.
In Central America, a megadrought between 1149 and 1167 probably brought instability to the Toltec state. It’s important to note that the megadrought between 1514–1539 weakened the Aztec state just prior to Spanish conquest. Europe and Asia have also had their share of megadroughts. Research shows severe megadroughts in Asia in the 1300s and early 1400s may have helped cause the collapse of Cambodia’s vast Khmer Empire.
Megadroughts in Australia
While many Australians may remember the severity of the Millennium Drought between 1997 and 2009, it has been discovered that this drought wasn’t particularly unusual. Megadroughts of the same or greater severity have occurred over the past 1,000 years across several parts of Australia and were relatively common over much of eastern Australia. This includes megadroughts between 1500 and the 1520s, and between the 1820s and 1840s. During a relatively short dry period between 1789 and 1795, which coincides with a European invasion of the continent. This period included several years of severe drought. 1792 in particular was an extremely dry year over almost all of eastern Australia.
Western Australia’s wheat belt is currently experiencing a decline in rainfall. This, of course isn’t unusual especially when compared to past droughts in that region. Tree rings reveal that longer, more severe droughts occurred in that area no less than six times in the last 700 years. These periods include the years 1393–1407, 1755–1785, and 1889–1908. As far away as Tasmania, evidence suggests that prolonged dry periods occurred in the latter part of the 16th century with a shorter but more severe downturn from 1670–1704.
How can we be better prepared to handle megadroughts in the future?
Water management in Australia has relied on short instrumental data which does not capture the full range of variability in its rainfall. What does this mean? Well, for example, it suggests that Australia’s infrastructure may be inadequately designed or managed to cope with major flood events or prolonged dry conditions.
Now, even relatively short but very dry periods can lead to major problems. This was evident in Tasmania during the summer of 2015 and 2016 when, after a dry winter and spring, the water levels in major catchments were minimal and fires raged in the west. The Basslink cable, which connects Tasmania to the national grid, broke resulting in the use of diesel power generation to keep power on in the state.
Future megadroughts will amplify the pressures on already degraded Australian ecosystems. From Australia’s recent past, experts understand that the harm relatively smaller droughts can impose on the environment, the economy, and Australians’ mental and physical health. Careful consideration must be given as to whether current management regimes and water infrastructure are fit-for-purpose, given the projected increased frequency of megadroughts.
It’s difficult to plan effectively without fully understanding even natural variability. This means that Australian scientists and policymakers need a better understanding and appreciation of the data from archives such as tree rings, corals and ice cores, all of which provide crucial windows to the continent’s distant past.
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