Melbourne: Climate and water
For the water account period 01 July 2022 - 30 June 2023
- Total annual rainfall during the 2022-23 year was above average for the fourth consecutive year and the highest since 2010-11.
- With the influence of a negative Indian Ocean Dipole and La Niña, spring rainfall was very much above average.
- Soil moisture in the root zone (0–1 m depth) was predominantly average to above average across the region.
- Total annual flows in the region's major rivers were the highest on record at all sites except for the Bunyip River at Iona, which had its fourth highest streamflow on record.
For further information on the region's climate and water conditions during the 2022-23 year scroll down this page or click on the links below:
About the region
- The Melbourne region has a temperate oceanic climate, characterised by four dinstinctive seasons, with cold to mild winters, and warm to hot summers.
- Rainfall is generally uniform throughout the year, but higher totals are more common during the winter and spring months (June to November).
- Streamflows in the region's rivers typically reflect the distribution of rainfall throughout the year. Higher streamflows and storage inflows occur during winter (June to November), while less streamflow occurs during the summer months (December to February).
Climate conditions
Rainfall
Figure C1 Annual and monthly rainfall deciles for the Melbourne region during the 2022-23 year
- Total area-averaged rainfall for the 2022-23 year was 1,057mm, 23% more than the mean value of 861mm. It was the region's ninth wettest year since records began in 1900.
- A negative Indian Ocean Dipole event was active between August and December 2022 (Climate Driver Update) and in September 2022 a third consecutive La Niña event was declared active in the tropical Pacific Ocean (Climate Driver Update) and remained active through to March 2023. Both a negative Indian Ocean Dipole and La Niña generally increase the chance of above average rainfall in the region in winter to spring and spring to summer respectively.
- Rainfall was very much above average across most areas during August, October and November, with the region experiencing its third wettest spring on record.
- In October 2022, a series of low pressure systems and surface troughs drew tropical air from the warm ocean waters, delivering thunderstorms and heavy rain to the region and resulted in the region's wettest October on record. Rainfall totals were more than doubled the monthly average, with widespread flooding occured around the region. More information on this event can be found in the Bureau's Special Climate Statement 77.
- In contrast to the wet spring, summer rainfall was average to below average across the region, with January 2023 and February 2023 being particularly dry.
- Autumn saw the return to average to above average rainfall through to the end of the 2022-23 year.
- More information on Australia's climate and water over the 2022-23 year can be found at: Financial year climate and water statement 2022-23.
Figure C2 Total monthly rainfall for the Melbourne region during the 2022-23 year compared with the average and percentiles for the region
- Rainfall was above the 90th percentile for August 2022, October 2022, and November 2022, following high rainfall events across these months.
- January 2023 and February 2023 were particularly dry, but remained above the 10th percentile.
- No month ranked below the 10th percentile.
Actual evapotranspiration
Figure C3 Annual and monthly actual evapotranspiration deciles for the Melbourne region during the 2022-23 year
- Total area-averaged actual evapotranspiration for the 2022-23 year was predominantly above average across the region, with some smaller areas experiencing very much above average evapotranspiration.
- Due to significant rainfall leading to higher water availablility, evapotranspiration was above average for the first half of 2022-23, with the exception of eastern half of the region in July and September.
- Drier conditions over summer saw evapotranspiration drop to average or below average in February and March 2023, while a return to higher rainfall from autumn onward resulted in above average evapotranspiration over this period, particularly around Melbourne area.
Soil moisture
Figure C4 Annual and monthly soil moisture deciles for the Melbourne region during the 2022-23 year
- Soil moisture in the root zone (0–1 m depth) for the 2022-23 year was predominantly average to above average across the region following another year of above average rainfall.
- While soil moisture at the start of the 2022-23 year was mostly drier than average, heavy spring rainfall increased soil moisture to very much above average conditions by November and through into December 2022.
- Below average rainfall throughout January 2023 and February 2023 resulted in a decrease in soil moisture, with some areas in the northeast experiencing very much below average soil moisture.
- From April to June 2023, the soil moisture was average to above average across the region, reflecting the average to above average rainfall during those months.
- More information on soil moisture distribution across the Melbourne region is available in the Australian Water Outlook.
Streamflow responses
Figure C5 Key flow gauging stations along the
main rivers within the Melbourne region
- There are four primary river catchments within the Melbourne region: Bunyip, Yarra, Maribyrnong and Werribee.
- Streamflows in the Maribyrnong, Werribee, and Yarra rivers are influenced by diversions for consumptive use, dam operations, and dam spills. The Bunyip River is less influenced by these factors.
Figure C6 Total monthly flow for major rivers in the Melbourne region during the 2022-23 year compared with the average and percentiles
- With the exception of the Bunyip River at Iona (Station 228213A), total annual flows in the region's major rivers were the highest on record at all sites during the 2022-23 year, following the region's fourth consecutive year of above-average rainfall. The Bunyip River at Iona experienced its fourth highest total annual flow on record.
- Following high August rainfall, the Bunyip River at Iona and the Werribee River at Wyndham Vale (Station 231204A) peaked above the 90th percentile.
- All sites recorded their highest October flows on record including some periods of flash flooding after the region experienced its wettest October on record. With continued high rainfall, streamflows remained at or near record flows during November 2022.
- Despite streamflow volumes decreasing from mid summer into autumn, which is typical for the Melbourne region, they remained near average or above average due to above average rainfall from March to June 2023. The Yarra River at Banksia Street, Heidelberg (Station 229135A) trended close to or above the 90th percentile throughout the last six months of the 2022-23 year.