Melbourne: Climate and water

  • Total annual rainfall was above average for the second consecutive year.
  • Streamflows were high reflecting the relatively wet conditions over the region.

Schematic representation of the Melbourne region. In 2020–21, rainfall was 867 mm, marginally above average. Streamflow in Yarra River in 2020–21 was 608 GL compared to the average value of 374 GL. Soil moisture was above average.

For further information on the region's climate and water conditions during the 2020–21 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 2020–21 year

 

  • Total area-averaged rainfall for the year was 867 mm, slightly more than the mean value of 861 mm.
  • Above-average rainfall in October 2020 and January 2021 was due to several cold frontal systems crossing the region during those months. In January 2021, rainfall was above average over the entire region.
  • Above-average rainfall in June 2021 was likely due to a negative Indian Ocean Dipole pattern that influenced Australia's climate during this period. Rainfall was well above average in the north over the upper catchment areas of the region's major river systems.

 

 

Figure C2 Total monthly rainfall for the Melbourne region during the 2020–21 year compared with the average and percentiles for the region

 

  • Rainfall was well above the 90th percentile in January 2021. It was the region's wettest January since 2011.
  • The rainfall during July 2020 was very low; it was the driest July in almost 20 years.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Melbourne region during the 2020–21 year

 

  • Total area-averaged actual evapotranspiration was average to above average across most of the region.
  • Evapotranspiration was well above average over large parts of the region during August 2020 and November 2020 due to higher water availability following above-average rainfall in August 2020 and October 2020 respectively.
  • Evapotranspiration was above average across almost the entire region in June 2021 reflecting the increased water availability during a wet start to the 2021 winter.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Melbourne region during the 2020–21 year

 

  • Soil moisture in the root zone (0–1 m depth) was average to above average across most of the region.
  • Soil moisture was average over most of the region in August 2020 following average winter rainfall.
  • In February 2021, soil moisture was above average over almost the entire region following high rainfall in January 2021.
  • By June 2021, soil moisture was average to above average over large parts of the region following a wet start to the 2021 winter.
  • 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 spills. The Bunyip River is less influenced by these factors.

 

 

Figure C6 Total monthly flow for major rivers in the Melbourne region during the 2020–21 year compared with the average and percentiles

 

  • In 2020–21, streamflows were above average for the second consecutive year. For example, total annual flow in the Yarra River at Banksia Street Heidelberg (Station 229135A) was 608 GL compared to the average value of 374 GL.
  • Streamflow was relatively high across the region during late winter–early spring, particularly in the Yarra River, the region's largest river, due to above-average rainfall in August and October 2020.
  • In June 2021, streamflows were well above average following very high rainfall during that month, particularly in the north over the upper catchment areas of the region's major river systems (see Rainfall).