Tag: BOM


South Australia sweats it out through driest year on record in 2019


Adelaide 5000

South Australia suffered its driest year on record during 2019, the Bureau of Meteorology (BOM) says, with rainfall down 65 per cent as mean temperatures rose 1.45 degrees Celsius higher than the long-term average.

Key points:

  • Every month except August endured above-average temperatures in SA, with a record dry spell between January and April
  • Average rainfall in the state was down 65 per cent to become its driest year on record
  • Adelaide endured its hottest day on record on January 24 when it reached 46.6C, beating the mark set 80 years earlier

Releasing the 2019 Annual Climate Statement today, BOM head of climate monitoring Karl Braganza said every month apart from August endured above-average temperatures in SA, while there was a record dry spell between January and April.

“It was very dry, the driest year on record, with average rainfalls of about 80 millimetres [down 65 per cent from the long-term average],” he said.

“We’ve got several locations throughout the interior where we got less than 30mm rainfall for the year.”

The bureau said 2019 was South Australia’s second hottest year on record.

Adelaide endured its hottest day on record on January 24 when it reached 46.6C, beating the 46.1C recorded in 1939.

Lake Eyre fills despite big dry

Australia’s annual mean temperature was 1.52C above average and its overall rainfall down 40 per cent.

This is despite February’s Townsville floods, which exceeded local rainfall records.



Photo:

Floodwaters near Birdsville make their way towards Lake Eyre during February. (Supplied: C. Ellis)

“What we did see is the floodwaters eventually making their way to Lake Eyre or Kati Thanda,” Dr Braganza said.

“That’s the most significant filling of the lake since 2010-11 in the midst of all the rainfall deficiencies around that location.”

Australian maximums up 2C

Dr Braganza said daytime temperatures across the country in 2019 were above their average maximums by a whopping 2.09C for the first time in recorded history.

“We also saw the six hottest days on record, peaking at 41.9C [on average across the country],” he said.

“We saw 11 such days where the national daily temperature [on average] went over 40C this summer, and that is really quite stark.



Photo:

A map revealing above average temperatures Australia-wide during 2019. (Supplied: Bureau of Meteorology)

“There were two such days in 1972-73, two in 2013, seven last summer and 11 this summer. So that’s really indicative of how widespread that heat is.”

Dr Braganza said there were multiple factors behind the hot and dry weather including a strong Indian Ocean Dipole (IOD) event, or sustained change in the difference between sea surface temperatures in the western and eastern Indian Ocean.

There was also a rare and sudden stratospheric warming event above the South Pole which pushed Australian weather systems northward and “compounded the warmer and drier than average conditions over southern Queensland and New South Wales during spring, amplifying the fire weather”.


Video: This is how sudden stratospheric warming occurs

(ABC News)

Global warm a ‘key factor’

Dr Braganza added that global warming had been a “key factor” because Australia had warmed by more than one degree since 1910 — mostly since the mid-20th century.

“You can consider that most of the weather is occurring in a climate system that is about one degree warmer,” he said.

“So that will tend to push things towards record territory.

“We’ve got very well-defined and clear trends underlying the changes we’ve seen over the past couple of decades.”

External Link:

The weather bureau's outlook for January to March

Dr Braganza said a delayed monsoon season, which typically helped to cool the country’s interior, had also contributed to hot weather over summer.

“There’s nothing really indicating that things will cool down too much over the next few months, although we are starting to see some signs that the monsoon season is starting to get active,” he said.

BOM’s climate outlook overview, released last week, found that SA and Western Australia could receive average to wetter-than-average conditions in January, despite eastern Australia remaining drier than average.

That potential for wetter conditions was expected to weaken through February and there was no strong tendency towards wetter or drier-than-average conditions up to April.

BOM said days and nights were likely to remain warmer than average through to April.

Source: https://www.abc.net.au/news


2019 was Australia’s hottest and driest year on record


Adelaide 5000

The data is in and 2019 has topped the Bureau of Meteorology’s (BOM) charts for average and maximum temperatures as well as the lowest annual rainfall across the country.

Key points:

  • Australia’s annual mean and maximum temperatures both broke records set in 2013
  • The national area average rainfall was the lowest on record going all the way back to 1900
  • The hot and dry conditions are the result of a strong Indian Ocean Dipole and background warming

It will come as no surprise to those suffering through this horror fire and heatwave season that the conditions leading up to it were the worst on record.

The new figures arrived as large parts of the country brace for more dangerous fire conditions over the next few days.

BOM will comment when its official report comes out next week, but the numbers speak for themselves.

Australia’s annual mean temperature was 1.52 degrees Celsius above the 1961-90 average of 21.8C — well above the previous hottest year (2013) at 1.33C.

External Link:

The difference in annual mean temperatures from the 1961-90 average

Also, the daytime temperature record was smashed, with the average maximum temperature of 30.69C coming in 2.09C above the 1961-90 average.

The previous record, set in 2013, was 30.19C.

External Link:

The difference in annual maximum temperatures from the 1961-90 average

Overnight temperatures didn’t surpass the record, but they were still the sixth hottest on record and well above average at 0.95C over the 15.1C 1961-90 average.

Meanwhile the drought has dragged on.

The national average rainfall total for the year was 277.63 millimetres, well below the previous record of 314.46mm in 1902 during the federation drought.

External Link:

Australia's annual rainfall from 1900 to 2019

The 1961-90 period is an internationally used standard as a period of good weather records used for data comparisons.

These values are calculated based upon gridded data from across Australia.

The country is broken up into a 0.05-degree grid by longitude and latitude, which is roughly 5km by 5km, with each grid assigned a maximum temperature based on the weather stations around it.

The average of all of the grids for every day of the year is then output.

Using the same gridded dataset, Australia broke the record for its hottest day on record two days in a row last month, with the nation’s average maximum temperature smashing the previous record (40.3C) to reach 40.7C and then 41.9C a day later.

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Why so hot?

The record-breaking year was especially noteworthy because it occurred without an El Nino event, the climate driver most commonly associated with hot dry conditions in Australia.

While the Pacific Ocean remained neutral, the main climate driver was the incredibly strong positive Indian Ocean Dipole (IOD).

The IOD has been working to generate rising air and rain over eastern Africa but hot descending air over Australia.

It is associated with drought and hot conditions over eastern Australia as well as with a delayed monsoon, all of which have been the case this summer.

Late last year, an unusual sudden stratospheric warming (SSW) event also added to the hot dry conditions by shifting the westerly winds, which usually lurk over the Southern Ocean, up onto the continent.


Video: This is how sudden stratospheric warming occurs

(ABC News)

This event was also associated with a strong positive phase of the Southern Annular Mode (SAM), again encouraging hot dry conditions.

And this is all on top of the anthropogenic global warming trend; BOM records show Australia has warmed by just over a degree since 1910, with most of the warming occurring since 1950.

What now?

Thankfully the positive IOD and negative SAM have decayed and the BOM’s outlook for the next three months is decidedly more neutral for rainfall, although temperatures are likely to remain above average for most of the country.

It is finally beginning to look like more tropical weather is returning to our north, with the chance of a cyclone developing early next week and tropical rainfall expected to move into inland Western Australia over the next few days.

But for those in the south, while a return to neutral conditions is better than drier than average, average conditions over summer are still hot and dry.

Until there is widespread rainfall, fire and heatwave conditions will continue.

External Link:

The weather bureau's outlook for January to March

Source: https://www.abc.net.au/news