Sydney is having its wettest March on record and its wettest calendar month in more than 30 years, with March now overtaking June as Sydney's wettest month of the year.

The combination of La Niña, an abnormally warm Tasman Sea, and a predominantly positive Southern Annular Mode (SAM) caused prolific rain in Sydney this month.

As of 9am on Wednesday, March 30, the city’s Observatory Hill rain gauge had received 537 mm of rain so far this month. This is the highest monthly total on record for March, beating 521.4 mm from 1942. It is also only the second time in 164 years of records that Sydney has seen half a metre of rain in March.

March 2022 has also become Sydney’s sixth wettest calendar month on record, and the city’s wettest month since February 1990.

Records have also been broken in other parts of the Sydney basin this month.

The running monthly total at Richmond RAAF had reached 589mm by 9am on Wednesday, March 30. This was a new monthly record for the RAAF base at any time of year, with records available back to the 1920s.

Image: Flooding in Camden during heavy rain in the opening week of March. Source: @lillyraemedia / Instagram

March has traditionally been Sydney’s second wettest calendar month based on long-term averages, behind June. However, exceptionally high March rainfall totals in the past two years have rewritten the city’s climatology.

Up to 2020, the long term rainfall averages for March and June were 131.6 mm and 133.1 mm. However, including rainfall observations from 2021 and 2022 to date, the long term average for March is now 135.8 mm and June is 132.7 mm.

This shift in long-term rainfall averages aligns with a broader trend of reducing cool-season rainfall in southeastern Australia in response to climate change.