After a year of heavy rain and widespread flooding, updated data has confirmed several locations across New South Wales experienced their wettest 12 months on record.
Annual records fell from the state's Riverina in the west, to the Northern Rivers and Illawarra on the coast.
Lake Cargelligo, in the Central West, was among the sites that easily topped their yearly rainfall total.
A weather station at the airport recorded 925.5 millimetres, the highest in almost 140 years of record keeping.
Judging a record
Bureau of Meteorology senior climatologist Hugh McDowell said records set at older weather stations were of most interest.
"The most rainfall in the last 20 or 30 years at these sites is still fairly significant," he said.
"The long-term records though, they do really give you a sense of how extraordinary the rainfall may have been this year."
Australian National University climatologist Janette Lindesay said climatologists used 30 years of records as the benchmark for determining if a record had been set.
"If you take shorter periods you can have your averages skewed towards drier conditions or wetter conditions," she said.
Other areas with a long history of records that have broken records include:
- Kiama: 2,803.8mm [109 years of records]
- Jervis Bay: 2,621.8mm [105 years of records]
- Temora: 991.0 [76 years of data]
- Condobolin: 962.4mm [68 years of records]
- Tabulam: 1,925.8mm [52 years of records]
- Lostock Dam: 1393.1mm [53 years of records]
This year was also officially Sydney's wettest, with the record being broken at Observatory Hill.
Records set but gaps in data
Ms Lindesay said in the past, people recorded data which meant there could be gaps or errors, leading to inaccurate records.
"There are quite a lot of missing months of data which means you don't end up with an annual total for that particular place for that year," she said.
Locations that broken records but have a short history or gaps in data include:
- Griffith Airport: 841.4mm [60 years of records but there are significant periods of missing data]
- Nowra: 2,480.0mm [47 years of records]
- Cessnock: 1,219.0mm [33 years of records]
- Ulladulla: 2,481.0mm [28 years of records]
- Evans Head: 2,094.8mm [25 years of records]
- Dorrigo: 2,845.8mm [25 years of records]
Year of heavy rain
Significant rainfall in NSW this year has been linked to a combination of La Niña, a negative Indian Ocean Dipole and a positive Southern Annular Mode.
There have been several devastating flood events, such as in Lismore, Eugowra, Forbes and the Murray River region.
Ms Lindesay said there were many factors at play when it came to linking rainfall and flooding.
She said coastal catchments were more prone to flooding from immediate rainfall, while inland catchments were more likely to flood as water made its way down river systems.
"There are direct relationships between rainfall and flooding in some areas and other relationships that are less immediate and direct," she said.
Ms Lindesay said flooding depended on there having been "pre-wetting" of the environment.
"If the environment is very dry and it rains you get surface runoff, but it may not make its way all through the river system," she said.
"You need to have some wetting of the soil so the water doesn't have anywhere to soak in."
Impacts of climate change 'complex'
Mr McDowell said climate change was contributing to warmer temperatures and warm air had the capacity to contain more moisture, so there was a chance it was contributing to more rainfall.
But he said the link between climate change and setting rainfall records was complicated.
"Climate change is also affecting the drivers and how that rainfall is distributed across Australia," he said.
"Under future scenarios we're looking at a reduction in winter rainfall across NSW.
"So it's not just a cut and dry decision between warmer air, more moisture, more rainfall, it's kind of more complex than that."
