Understanding the Magnitude of the Current Drought in NSW & QLD

In Australia, we’ve become so used to hearing the term “drought” that many people have become desensitised to it.  As such, it can be difficult to comprehend the magnitude of the current rainfall deficiencies currently being experienced by farmers across areas of the country – particularly across northern NSW and southern Queensland where years of failed wet and storm seasons has yielded some of the lowest rainfall totals on record.  More concerning is that many of these locations have very long rainfall records – some dating back over 140 years.

To demonstrate the extent of this drought we have gone through rainfall records in Stanthorpe, Moree, Armidale and St George – all of which are experiencing their driest first 8-months of the year on record, and some only receiving a fraction of their average rainfall so far.  Many other locations are in the same position – but these sites have long-standing rainfall records pushing well into the 1800s which helps illustrate how significant the lack of rainfall is compared to previous years.

One of the significant culprits to our unusual rainfall patterns has been the unusual sea surface temperature patterns experienced.  The positive IOD (Indian Ocean Dipole) due to relatively cooler water located in the eastern Indian Ocean has played a large role in recent rainfall deficiencies.  However the elephant in the room has been the Pacific Ocean where last year the atmosphere effectively decoupled from the oceanic sea surface temperature patterns.  This was amplified by the lack of a clear oceanic signal, with sea surface temperatures not fitting into the normally accepted El Nino, warm neutral, neutral, cool neutral or La Nina classifications.

A map produced by the Bureau of Meteorology shows the current 2-year rainfall deciles across the country.  Large portions of northern NSW and southern Queensland are sitting at their lowest rainfall on record – with well below average rainfall extending across much of NSW, eastern South Australia and the southern half of Queensland.

 

A look at the last 2 year rainfall as the percentage of the mean is just as concerning – with large portions of the region experiencing just over half their average rainfall.  This may not sound like a significant decrease, but considering many of these locations only receive 500-600mm a year, half of this brings the rainfall into the vicinity of 250-300mm.  To put this rainfall into perspective, most deserts receive up to 200mm a year which puts the rainfall for the last couple of years in our prime agricultural areas in the order of being desert-like!

 

Stanthorpe

The town of Stanthorpe in far southern Queensland has been one of the hardest hit regions and is expected to run out of water by the end of this year.  Successive dry years have culminated with the driest first 8-months of the year to generate a dire situation.  By the end of August, Stanthorpe typically averages 472mm of rainfall – this year they’ve had just a fraction over 136mm which is just a third of the average rainfall they should normally receive by now.   This is also well below the previous record of 180mm for the same period in 1902.

The annual average is 766mm and the previous driest year on record is 368mm back in 1957.  That means Stanthorpe needs to receive over 230mm for it NOT to be the driest year ever recorded – which may unfortunately prove to be all too achievable unless the spring storm season kicks in quickly.  Storms in spring are fairly common in the Stanthorpe region though the past couple of years has seen below average numbers combine with the lack of any summer rainbands to generate the dry conditions.  Last year a total of 568mm fell – which is still well below the 766mm of rainfall that normally occurs.

 

St George

Moving west to St George, rainfall has similarly been just as dire.  Just 86mm has fallen during the last 8 months – of which no rain fall at all during the height of summer in January and February.  86mm is less than a third of the average which should be 280mm for the year and is another unwanted record low rainfall statistic.  The previous driest for this period was 88mm in 1965, while other dry years included 99mm in 1902 and 106mm in 1915. 

Once again – this record dry periods comes off the back of not just one, but two dry years.  The annual average rainfall in St George is 478mm.  Last year, 2018 had 304mm while 2017 and 361mm – both substantially below average.  St George needs nearly 400mm in the next 3.5 months just to get average rainfall for the year!  The driest year on record was 125mm in 1915 – this year experienced most of its rainfall during winter when nearly half of the rainfall fell during July and August.  However thankfully was preceded by a year of average rainfall in 1914 with 470mm and above average rainfall in 1916 with 660mm.  Once again, the issue isn’t just record low rainfall for the last 8 months – the issue is that this comes off the back of two dry years prior.

 

Moree

The town with the greatest deficiency is Moree – where the lack of this year’s summer storm season was all too apparent with just 5mm occurring for the months of January and February.  The total rainfall between January and August was a paltry 83mm – the average in January alone is nearly that!  This means that Moree has had less than a quarter of its average rainfall for this period.  The only years to come close to this still managed more than 100mm with the second driest first eight months of the year recorded in 1902 (109mm)b and the third driest in 1965 with 118mm.  1902 was also the driest year ever recorded for Moree with 203mm recorded.  This means Moree needs more than 110mm for it NOT to be the driest year on record and nearly half a metre of rain in the next 3.5 months just to get up to the average of 577mm!

 

Armidale

The city of Armidale – while receiving more rainfall than other locations further inland such as Moree and St George is also within the grips of a record breaking drought.  Armidale has had 208mm for the year so far – that’s less than half the average of 438mm for the same time period.  It’s also the driest first eight months on record – beating the previous record set in 1965 when 221mm fell.  After that you need to go all the way back to 1888 when 253mm fell which is now the third driest for this period.  Armidale started off with some reasonable rainfall totals in January and March but since the end of March the city has had just 40mm occur over a five month period. 

Armidale is traditionally a wetter place than St George and Moree with its positioning on the ranges allowing it to generally receive rainfall all year round (with a late spring – summer bias thanks to orthographically induced storm activity).  The average is 763mm meaning Armidale needs over 550mm just to achieve its average rainfall for this period.  For perspective, in order to achieve this, Armidale would need to have its wettest October, November and December on record! 

The driest year ever recorded in Armidale was in 1874 when 421mm fell (the second driest year was 436mm in 1861).  More than 200mm of rain (ie double what’s already fallen so far this year) is needed for this NOT to be the driest year ever recorded.