March 2021 could be remembered as ‘the big wet’ in future annals.
After multiple days of persistent, heavy rainfall between March 17 and 26, much of the state was experiencing record flooding.
By Wednesday 24th March in fact, the Hunter region, like much of coastal NSW and Sydney, experienced its wettest week since national daily rainfall records began in 1900.
During that week of soaking, flooding occurred in most coastal catchments in New South Wales, reaching record heights on the Hastings and Manning Rivers and the Hawkesbury–Nepean catchment in Sydney – its most significant flooding for more than 30 years.
New South Wales had its second-wettest day, third-wettest week and second-wettest March on record since 1900.
Bureau of Meteorology senior climatologist Blair Trewin says March’s week-long rain pattern was “an exceptional event”.
“What made it stand-out was that it was wet everywhere,” he said.
“Usually it’s localised rain and flooding, like the pattern in 2015, but this time around the whole NSW coast was affected.”
Mr Trewin, who has more than 23 years experience in the industry, said Newcastle Airport collected record rainfall between 17th and 26th March.
“Williamtown recorded 331 millimetres over the five days,” he said.
“Although it had no one day over 100mm, it had five consecutive days with more than 40mm, making it the highest total on record for that site.”
Prior to peak rainfall on March 18, Hunter residents were being urged by NSW Premier Gladys Berejiklian to stay at home as emergency services battled to keep up with the number of calls for assistance.
NSW State Emergency Services and NSW Police also followed suit, issuing several warnings about flood waters via the media.
The 2020–21 La Niña weather event also meant pre-existing soil moisture, runoff and water storage levels were higher in March 2021 than for a similar multi-day coastal rainfall event in February 2020.
La Niña, Mr Trewin advises, is now at its tail end.
“The outlook for winter is fairly ordinary,” he said. “Rainfall will see no significant shift and there is a 70 to 80% chance of above average temperatures.”