ABC: Tyne Logan
)After the blistering heat of summer, many welcomed March 1 as the start of autumn's cooler nights and mild days.
In WA's South-West, the local Indigenous people also say a new season is beginning — but not because the calendar has ticked over into March.
With the first three weeks of March this year bringing heavy rain that tripled monthly averages in the space of hours, a string of warm nights not experienced in a decade, and a weekend of 37 degree days in the city, the advent of this week's cool change makes it clear there has been a shift.
Signs of the new season
Supplied: South West Aboriginal Land and Sea Council
)The season of Djeran, typically experienced over April and May, is one of the six Noongar seasons.
The others are Birak (December to January), Bunuru (February to March), Makuru (June — July), Djilba (August to September) and Kambarang (October to November).
Noongar Boodja country covers the entire south-western portion of Western Australia, approximately from Jurien Bay to Esperance and everywhere west. It's one of the largest Aboriginal cultural blocks in Australia.
There's no exact date to the start and finish of a new season — instead that's defined by the changes in the natural environment.
Here's what to look out for to signify the start of Djeran, according to Indigenous elder and Noongar man Noel Nannup.
Shift in wind direction
The first key sign is the wind change.
"The primary thing is the wind shift from the north-east to the south-west," he said.
ABC Weather: Kate Doyle
)The change of direction has been felt this week in Perth, with a ridge of high pressure sitting over land around the south of the state, rather than further south over water.
This is due to what's known as the subtropical ridge, a belt of high pressure systems that circle the southern hemisphere's mid-latitudes.
During the summer (Birak and Bunuru), it tends to sit over southern Australia, bringing dry weather and warm, easterly winds, but it migrates north as we head towards winter (Makuru), driving westerly winds.
Blossoming gums and banksias
The second key sign is blossoms blooming on certain native plants — in particular the banksia and gum trees.
ABC: Tyne Logan
)"The one that is dominating is the marri, which of course has the beautiful off-white, bone coloured flowers," he said.
"They are an indicator to us that (this year) there will be an early break to the season because they have been so prolific in their flowering."
Mr Nannup said when the marri was flowering, it usually took a couple of a weeks to see the full scope of the weather change.
ABC Local: Anthony Pancia
)Other plants to look out for include the candlestick banksia, which begins to grow a miniscule bud at the centre point of its leaves, and the black seeds within the grass-tree flower.
According to the Bureau of Meteorology's Noongar calendar, written by Noongar man Jason Barrow, Djeran is also a "time of red flowers" especially from the red flowering gum, the summer flame and also the red 'rust' and seed cones forming on male and female sheoaks.
ABC: TyneLogan
)Mr Nannup said when looking for the plant indicators, it was important to make sure the plant was in its native environment for the forecast to be accurate.
Migrating birds and animals
The next thing to observe was the movement of animals, he said.
"Particularly now, you have the pelicans starting to group together and they will head north," he said.
The observation of flying ants in the light winds can also be an indicator of the changing season.
Supplied: Keith Broadbridge
)For those who dislike spiders, Djeran brings good news
"When it gets really cold and starts to cool off overnight, most of the spiders die," he said.
ABC South East SA: Stuart Stansfield
)"You've got three or four different types: some occupy the high canopy, some the middle and some down low.
"The ones down low, where it's going to be really cold, all die, but they've laid their eggs under the bark and in curled leaves and (when they hatch) they are good seasonal indictors as well (for warmer weather)."
Variations in weather across regions
With Noongar country covering close to 200,000 square kilometres of land, there is no surprise that the climate can vary considerably across the different regions.
Mr Nannup said it was often the case that the new season would start in one part of the nation, but had not yet begun for another.
ABC: Tyne Logan
)"So if you went to Kalbarri right now, there are still wildflowers there, particularly the hakeas and leschenaultias, whereas down here that's gone."
A truer representation of seasons
The Indigenous seasons are looked at with high regard from meteorologists.
BoM senior forecaster Joe Courtney said having essentially four months of summer in the Noongar seasons, made up of Birak (first summer) and Bunnuru (second summer), was more appropriate to the weather experienced in southern WA.
"Our summers can go well into March and even the start of April," he said.
ABC Weather: Kate Doyle
)"I think the appeal of using Noongar seasons is that it has a much wider relationship with what is going on in nature.
"We could probably use in (observing) what crops might do as well, such as from an agricultural point of view, whereas our standard four seasons are much more crude."
Do conventional seasons fit our climate?
Generally speaking, yes.
Mr Courtney said they do broadly fit the warmest and coolest months of the year across the country.
ABC: Tyne Logan
)With set dates and national consistency, they are also more convenient for record keeping.
"The ease of the meteorological calendar is that it's by the first of the month, it's easy to say the summer is defined by these dates, and ... it's a bit easier to communicate what's going on across the country," he said.
