Melbourne: Climate and water

  • Total annual rainfall was above average, one of the few regions in Australia with high rainfall.
  • Streamflows were high reflecting the relatively wet conditions over the region.

 

Schematic representation of the Melbourne region. In 2019–20, rainfall was 952 mm, above average for the first time in three years. Streamflow in Yarra River in 2019–20 was 505 GL compared to the average value of 369 GL. Soil moisture was above average.

For further information on the region's climate and water conditions during the 2019–20 year scroll down this page or click on the links below:

 

About the region

  • The Melbourne region has a temperate climate and generally experiences mild winters and warm summers. Rainfall is relatively uniform throughout the year, but generally higher during the winter and spring months (June–November).
  • Typically, streamflow in the region's rivers reflects the distribution of rainfall throughout the year. Higher streamflows and storage inflows occur during June–November; less streamflow occurs during the summer months (December–February).

 

Climate conditions

Rainfall

Figure C1 Annual and monthly rainfall deciles for the Melbourne region during the 2019–20 year

 

  • Total area-averaged rainfall for the year was 952 mm, more than the mean value of 861 mm. Melbourne was one of the few regions in Australia with above-average annual rainfall in 2019–20.
  • The below-average rainfall during the spring and early summer months (September–December 2019) was due to a positive phase of the Indian Ocean Dipole, one of the strongest on record, that influenced Australia's climate during this period (see the Bureau's 2019–20 Climate Report for more information).
  • Rainfall was above average during the early part of 2020 as tropical moisture associated with warmer than average sea surface temperatures off the northwest coast of Australia moved across the continent and combined with southern cold fronts to produce high rainfall across the region.

 

 

Figure C2 Total monthly rainfall for the Melbourne region during the 2019–20 year compared with the average and percentiles for the region

 

  • Rainfall was well above the 90th percentile in April 2020. It was the region's wettest April since 1974.
  • The rainfall during December 2019 was very low and below the 10th percentile. It was the driest December in more than 20 years.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Melbourne region during the 2019–20 year

 

  • Total area-averaged actual evapotranspiration was average to above average across most of the region.
  • Evapotranspiration was below average during the latter part of 2019 due to low water availability following low rainfall in the spring and early summer months.
  • Evapotranspiration was above average over large parts of the region during February–June 2020 due to increased water availability following higher rainfall in the early part of 2020.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Melbourne region during the 2019–20 year

 

  • Soil moisture in the root zone (0–1 m depth) was above average across most of the region.
  • In July 2019, root-zone soil moisture was already average to above average following a wet winter in 2019. Dry conditions during the 2019 spring months meant that by December 2019, root-zone soil moisture was below average over most of the region.
  • Soil moisture was above average over large parts of the region during February–June 2020 following higher rainfall in the early part of 2020, particularly in April.
  • More information on soil moisture distribution across the Melbourne region is available in the Australian Landscape Water Balance.

 

Streamflow responses

Map of key gauging stations. Werribee River at Werribee Diversion Weir, station number 231204, is located in the southwest of the region. Maribyrnong River at Keilor, station number 230105A, and Yarra River at Banksia Street Heidelberg, station number 229135A, are near the centre of the region within 30 km of Melbourne. Bunyip River at Iona, station number 228213, is in the region's southeast.
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 spilling. The Bunyip River is less influenced by these factors.

 

 

Figure C6 Total monthly flow for major rivers in the Melbourne region during the 2019–20 year compared with the average and percentiles

 

  • Streamflows were above average in 2019–20, one of the few regions in southeastern Australia with higher flows.
  • Total annual flow in the Yarra River at Banksia Street Heidelberg (Station 229135A) was 505 GL compared to the average value of 369 GL. This was the first year of above-average annual flow in the river in seven years.
  • In July–September 2019, streamflow in the Werribee River was the highest on record for this 3-month period, reflecting the very wet conditions during the 2019 winter months over the upper reaches of this catchment area in the northwestern part of the region.
  • Streamflow was relatively low across the region during October–December 2019. In December 2019, there was no flow in the Werribee River.
  • During February–June 2020, streamflows in the major rivers were above average for almost the entire 5-month period following the higher rainfall across the region in the early part of 2020. Flows were above the 90th percentile during much of this period.