The Key To Avoiding Floods In Australia
Is Knowing When They Occur
Floods in Australia occur more frequently in the summer (December, January and February) than the winter months (June, July and August). Most of these summer floods occur in the northern parts of Australia. This coincides with northern Australia's wet season which runs from November-April.
The weather in northern Australia runs like clock work: you can almost pick the day when the rain will begin. However, trying to predict when it will stop raining is the difficult part.
In the south-eastern parts of Australia, floods can occur at any time of the year but the worst floods occur during mid-to-late winter (July and August) except if there's a low pressure system situated either no or
off the southern Queensland coast during the summer months.
In comparison, the south western parts of Australia are more likely to have floods in the winter since that's the time of the year when most of the rain falls.
There are two main types of floods in Australia:
- Flash floods
- Widespread flooding near river basins
Flash floods in Australia occur mainly due to severe thunderstorm activity. Some of these storms may only last 10-15 minutes but that is sometimes enough to transform a landscape into a raging torrent of mud and water.
The amount of rain that falls depends upon whether its just one storm or a multiple of storms forming one after the other.
Desert floods in Australia
Most of these types of floods occur in inland regions of Australia during late summer through to early autumn.
Desert floods in Australia are often violent and only last for a short time. These rapidly moving flood waters carve the landscape into a mass of debris and muddy waters. Due to this you should never sleep too close to a river, especially if it's empty since you won't know how far the water level can rise to. The river bed may have been dry for a decade but that can change overnight if there's a storm.
Another major risk is when you don't even know about the storm that has hit an area upstream. You're happily swimming in a nearby creek under blue skies when you notice that the water in the creek suddenly feels colder. Of course you don't mind this
since it's a hot day. Unfortunately in a matter of ten minutes of so, a huge deluge of water is billowing towards you.
In this case the only indication of the impending flood was the drop in river water temperature. This may be the only warning sign
you'll get so take note of this if you're swimming in a river.
Flash Floods in Australia - Within Cities
Flash floods that occur cities also tend to be localised since the water is channelled along roads and footpaths. If the streets are without vegetation, the water simply congregates in the lowest-lying areas.
Since the city streets are canyon shaped, the water simply charges down the street picking up anything in its path.
Most of the storm drains are unable to handle the volume of water.
Please view the video footage (on the left) of car's in a car park being carried away by flash flooding in Toowoomba on 10th January, 2011.
Widespread floods in Australia
Major widespread flooding in Australia normally occurs as a result of either tropical cyclones, monsoonal activity or mid-latitude
low pressure systems.
If you're staying along the northern coastline of Australia, you have to be on the lookout for tropical cyclones from November-April. These tropical cyclones bring flooding rains to large areas in the vicinity of the tropical cyclone. Most of this rain is welcome but the damage isn't.
Most of the resulting damage along the coastline occurs as a result of a storm surge. These storm surges cause far more damage than the wind alone.
Just in case you don't know what a storm surge is. A storm surge occurs when the sea advances onto land. The sea-level rises in response to the lighter air within the tropical cyclone coupled with larger waves due to strong winds.
As a tropical cyclone passes over land it begins to weaken and slowly transforms into a rain depression. It's this rain depression that brings with it the widespread flooding. These rain events can produce up to 700 millimetres of rain in 24 hours.
Typically monsoonal activity in northern Australia occurs around the same time as tropical cyclone activity. The winds in northern Australia before the arrival of the monsoon typically swing in from the south east to the north east. When the monsoon season starts the winds shift direction and come in from the north west and west.
Torrential rain and gusty afternoon showers and thunderstorms are the order of the day during the monsoon season. Darwin, the capital city of the Northern Territory rarely misses out having a monsoon each year. As a result floods are common in this region.
The monsoon over northern Queensland is generally weaker than that over the Northern Territory because Papua New Guinea blocks the arrival of the some of the incoming north westerly winds.
You can expect rainfall totals up to 450mm in 24 hours at least twice a year during the monsoon season in northern Australia.
One of the worst inland floods in Australia occurred as a result of southward extension of the monsoon. This occurred back in February-March 1967. Rainfall totals of between 120-350 millimetres were recorded over the whole period. Although some locations received 150 millimetres in 24 hours.
Considering that this region of Australia can receive more rain overnight than it normally gets in a year makes this rainfall event exceptional. The inland regions of Australia normally have an annual mean rainfall of less than 250 millimetres.
Mid-latitude low pressure systems
As you can tell by the name, the low pressure systems occur in southern parts of Australia. They commonly occur in the winter months and can cause a great deal of flooding and damage to property.
Just before this small flood, the Avon river (shown in the photo on the left) was barely flowing.
The main rain bearing weather systems that lead to flooding in southern Western Australia are the result of vigorous cold fronts that have embedded thunderstorms. In addition, the cold front may join with the north-west cloud band. These normally occur in the winter months.
Severe floods in southern Western Australia do not occur very often but when they do, it normally causes extensive damage to towns in the area. Most of the buildings in this region of Australia aren't designed to prevent flood damage unlike many houses in eastern north Queensland and the Northern Territory.
In eastern Australia, most of these intense low pressure systems (known as east coast cyclones) form also in the winter months. They bring with them gale force winds and torrential rain to areas that stretch from south eastern Queensland to the eastern coastline of Tasmania. Generally though, the preferred location for east coast cyclones extends from mid-north New South Wales to far eastern Victoria. You can expect that the flooding from these weather systems will occur nearly every year so just be aware of this when you're travelling along the south east coast of Australia.
These east coast cyclones can produce up to 300 millimetres of rain in 24 hours and so most roads will become blocked by flood waters.Return from Floods in Australia to Australian weather page