WEATHER EXPLAINED: Why 2019 was warmest, driest on record
IN A special climate report from the Bureau of Meteorology, 2019 was revealed as the warmest and driest year on record for Australia as a whole.
Spring was also the driest on record nationally.
BOM said record low rainfall for the year occurred over large areas of inland Australia, which resulted in very low soil moisture levels over most of the continent leading into December.
"The very dry conditions continued through December. It was the driest December on record nationally, with rainfall below average nationwide.
"Record low December falls were experienced in scattered parts of northern and eastern Australia. Most areas of South Australia, New South Wales (apart from the northeast), and Victoria (apart from the eastern ranges and the southwest coast) had less than 10 millimetres for the month.
Why was it so dry?
One of the strongest positive Indian Ocean Dipoles on record was a substantial contributor to the dry conditions in the second half of the year, the BOM report reads.
"The Southern Annular Mode (SAM) was also in a persistent negative phase for much of the period from September to December (following a marked sudden stratospheric warming over the Antarctic in early spring), resulting in anomalous westerly flow over southern Australia.
"In spring and early summer, a negative phase of the SAM is typically associated with dry conditions in New South Wales and Queensland, and warm conditions over much of the continent apart from the southeast.
"The combination of these two climate drivers was highly favourable for dry conditions in the eastern States and above-average temperatures across the continent."
Extreme heat in December 2019 and January 2020
Summer 2019−20 was the second-warmest on record for Australia (after 2018−19).
A major feature of the heatwave for this period wasn't just the extremity of the heat, but the extent of it.
This saw in area-averaged records for the hottest day being exceeded for Australia, where "national area-averaged maximum temperatures were well beyond previous records".
Averaged over the country, Australia had its hottest day on record on December 18 2019; the average of 41.88C was far above the previous record of 40.3C set on January 7, 2013.
BOM said six other days in the month also exceeded the previous record.
"In total, 11 days during the month had a national area-averaged maximum of 40C or above, seven of them consecutively from 23 to 29 December.
"Prior to December 2019, there had been only 11 such days on record in Australia since 1910 (seven of which occurred in the 2018-19 summer)."
BOM said overall, December 2019 had the highest area-averaged maximum (4.15C above the 1961-90 average), minimum (+2.26C) and mean (+3.21C) temperatures on record for Australia.