BOM drops latest data review

Whew… what a hot summer… isn`t it?

If you thought that the weather has been hotter than usual, it turns out you’re right. According to the Bureau of Meteorology’s (BoM) annual climate statement, the annual national mean temperature last year was 1.52°C above average, making 2019 Australia’s warmest year on record.

Part of Menindee Lakes on the Darling River, which is under pressure from low water flow as a result of the prolonged drought. Dean Lewins/AAP

But temperature is only part of the story. Annual total rainfall across Australia in 2019 was 277.6 mm, and 40% below the long term national average of 465.2 mm.  As a result much of Australia was affected by drought, during the driest year on record.

Impacts around Australia (fire and drought)

While bushfires are a regular feature of the Australian calendar, such blazes have not ever happened on such a huge scale. These bushfires have had devastating and catastrophic effects on our communities, unique wildlife and bushland.

New South Wales and southern Queensland were both affected by drought, experiencing their driest conditions on record. Drought, bushfires, and heatwaves are badly affecting important sectors such as farming. The agricultural impacts of the recent bushfires have not yet been thoroughly assessed, but initial estimates suggest that the fire at Cobraball in Queensland had the largest impact on agriculture in recent history, burning through 12,000 hectares including 230 hectares of high-value horticultural crops. The damage bill for farms in this region has been estimated at $20 million (ABC 2019). In total, the direct cost to fire-affected regions from lost tourism, agricultural, and retail income is estimated at between $1.1 billion to $1.9 billion.

BoM’s head of climate monitoring Dr Karl Braganza said the record hot and dry year has been one of the key factors influencing recent and current fire conditions across the country.

Declining cool season rainfall has had a significant impact on increasing bushfire risk. Bushfire risk in parts of northeast New South Wales and southeast Queensland was exacerbated by below-average rainfall leading to a prolonged, severe drought and very high dryness factors for fuels. Soils also became very dry. Low soil moisture means high stress in vegetation and fuels that might not normally burn, making them more prone to bushfires.

Why is it so hot?

The main influence on Australia’s rainfall and temperature are our ocean’s oscillations. (El Nino-Southern Oscillation-(ENSO) and Indian Ocean Dipole (IOD) )

When ENSO is neutral, the main climate driver for Australia is the strong positive Indian Ocean Dipole. These conditions occurred in the second half of 2019 and have continued to persist. Positive IOD is associated with drought and hot conditions in eastern Australia, and a delayed monsoon (which happened this summer) made these conditions more severe.  All these factors made our national landscape tinder for bushfires.

What’s happened locally?

2019 was the warmest and second-driest year on record for Western Australia. Annual rainfall was 49% below average, with the State mean temperature 1.67 °C above average and half a degree warmer than the previous record in 2013.

In Perth itself, rainfall recorded at Perth Airport was only 524.9 mm in 2019 (compared to 762.1 mm annual average), which was its fourth driest year on record.

So, while we still in the middle of summer here in Perth and expecting to experience more heat next month (February is usually the hottest month of the year), these statistics are a good reminder that in the city we really need to prioritise mitigating the urban island heat effect if we’re to stay comfortable and healthy in our cities – and protecting and planting more trees (the right kind of trees!) is one of the best ways to start!

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