THE CLIMATE KELPIE BLOG: The good, the bad and the ugly – charting the impact of East coast lows
Extreme low pressures resulting in cyclonic winds, heavy rainfall and flooding sounds like something you’d expect in the tropics, but East Coast Lows can bring these tumultuous conditions to the southern part of Australia’s East Coast.
These phenomena have been profiled as the most unpredictable of the Climate Dogs: Eastie.
East Coast Lows near the coastline can have dramatic impacts on New South Wales, south-east Queensland, far-east Victoria and sometimes Tasmania. The impacts are felt most strongly on the coast and taper off towards the higher reaches of the Great Dividing Range.
Some of the more memorable media images include a swimming pool collapsing into the sea during severe erosion at Collaroy Beach on Sydney’s Northern Beaches in 2016 and the grounding of the bulk ore carrier Pasha Bulkar at Newcastle Beach in 2007.
The damage resulting from an East Coast Low is usually quite localised, but those on the fringes can benefit from increased rainfall and catchment inflows, and, on occasion, good snowfalls in the alpine resorts.
What is an East Coast Low?
East Coast Lows can be driven by a dynamic interaction between cold air in the high levels of the atmosphere over the continent, and the surface temperature gradient between the land and the relatively warm Tasman Sea air. They can develop rapidly in a variety of ways:
- The intensification of existing low-pressure systems
- Upper atmosphere disturbances
- In the wake of a cold front as it moves from Victoria into the Tasman Sea.
- In summer they can result from the decay of tropical cyclones as they move south
Warm sea surface temperatures associated with the East Australian Current are an important factor contributing to some aspects of their development, such as for causing intense rainfall.
East Coast Lows can happen at any time of year, but are typically more common in late autumn and winter, particularly June. They usually last for just a few days, unlike tropical cyclones which generally last for a week.
Typically, gales and heavy rain occur on and near the coast, south of the low pressure’s centre, while to the north of the low there can be clear skies. The results can often be quite dangerous at the epicentre with gale-force winds or the occasional tornado. Widespread and heavy rain can lead to both flash flooding and flooding of major rivers. On the coast extremely rough seas can damage sea vessels and lead to coastal erosion and inundation.
One-off events can dominate a region’s annual rainfall tally and explain a lot of the seasonal variability east of the Great Dividing Range. This means that they are also important for river flows and water availability for irrigation.
The June 2016 event, when erosion damaged properties at Sydney’s Collaroy Beach, had an unusually widespread impact with very heavy rainfall leading to flooding of 32 rivers in areas stretching from southeast Queensland, eastern New South Wales, eastern Victoria, and large areas of northern Tasmania.
Rainfall records were broken at many locations. For example, the three-day total was 580mm at Robertson in the NSW Southern Highlands (June 4 to 6) and 311mm at Yolla in Northern Tasmania (June 5 to 7).
In NSW alone, government estimates put losses to the agriculture and aquaculture industries at over $19 million with North and South Coast shellfish producers and the North Coast banana producers most affected. Other industries impacted included blueberries, beef, dairy, macadamias, pecans, nurseries, greenhouses and sugarcane.
Most East Coast Lows are smaller-scale systems whose major impacts are confined to a few hundred kilometres of the coastline.
While wind speeds are generally lower than those observed with tropical cyclones, a maximum gust of 165 kilometres per hour was recorded during an East Coast Low event in 1974 at Newcastle when the bulk carrier Sygna was wrecked at Stockton Beach. This wind speed is the equivalent of a Category 3 severe tropical cyclone.
When the Pasha Bulkar was grounded at Newcastle Beach in 2007, the maximum wind gusts recorded were a more typical 135 km/h.
Planning and preparation
Unfortunately, East Coast Lows can develop overnight and are very hard to predict. Thankfully, only around 10 per cent of these events cause extreme daily rainfall above 100 mm.
As well as being difficult to predict, the number of East Coast Lows that occur each year is highly variable and not related to large-scale climate drivers such as the El Niño-Southern Oscillation.
This variability makes it difficult to measure the impact of a changing climate on the future frequency of East Coast Lows and observations in recent decades show no clear trend in numbers. While current research suggests that the frequency is likely to decline in the future, the potential for coastal erosion and inundation is likely to increase due to rising sea levels.
East Coast Lows can bring much needed rain, but for those in the eye of the storm they present great risk. Agricultural businesses need to be aware of the potential for rapidly developing cold and windy conditions, heavy rain and floods. Those in flood-prone areas, or with young livestock or recently shorn sheep need to keep a wary eye on the Bureau of Meteorology Warnings and be ready to respond.
Bureau of Meteorology: What is an East Coast Low
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