National Water Account 2019

Melbourne: Climate and water

  • Total annual rainfall was below average across the region for the second consecutive year.
  • Streamflows were low reflecting the below-average rainfall and poor soil moisture conditions.

 


For further information on the region's climate and water conditions during the 2018–19 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 2018–19 year

 

  • Total area-averaged rainfall for the year was 691 mm, less than the mean value of 852 mm and the region's lowest rainfall in 10 years.
  • Rainfall in September 2018, typically one of the wetter months of the year, was very low across the entire region. Eastern and central parts of the region experienced their lowest rainfall on record for that month.
  • The below-average rainfall throughout the spring 2018 months was likely due to a positive phase of the Indian Ocean Dipole that influenced Australia's climate during this period (see the Bureau's 2018–19 Climate Report for more information).
  • Above-average rainfall during November–December 2018, as well as May–June 2019, was associated with low pressure systems and cold fronts that crossed the region during these periods.

 

 

Figure C2 Total monthly rainfall for the Melbourne region during the 2018–19 year compared with the average and percentiles for the region

 

  • Rainfall was above average during November–December 2018 and May–June 2019. All other months had below-average rainfall.
  • The rainfall during September 2018, January 2019 and April 2019 was very low and below the 10th percentile. It was the driest September since 1981 and the third lowest rainfall in April on record.

 

Actual evapotranspiration


Figure C3 Annual and monthly actual evapotranspiration deciles for the Melbourne region during the 2018–19 year

 

  • Total area-averaged actual evapotranspiration was below average across most of the region, reflecting the dry conditions and low water availability throughout most of the year.
  • Above-average evapotranspiration only occurred across most of the region during December 2018 due to the increased water availability following high rainfall in November–December 2018.

 

Soil moisture


Figure C4 Annual and monthly soil moisture deciles for the Melbourne region during the 2018–19 year

 

  • Soil moisture in the root zone (0–1 m depth) was well below average across most of the region; an area in the northwest experienced its poorest soil moisture conditions on record.
  • Rainfall and soil moisture are typically closely aligned. For example, below-average soil moisture conditions across the entire region during the 5-month period from January–May 2019 is due to very low rainfall that occurred during a 4-month period between January–April 2019.
  • Soil moisture conditions during the year were only average to above average in December 2018 following high rainfall in November–December 2018.
  • More information on soil moisture distribution across the Melbourne region is available in the Australian Landscape Water Balance.

 

Streamflow responses


Figure C5 Key flow gauging stations along the Bunyip, Yarra, Maribyrnong, and Werribee 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 key rivers during the 2018–19 year compared with average and percentiles

 

  • Streamflows were well below average for most of the year, which was influenced by the relatively low rainfall and very poor soil moisture conditions experienced across the region.
  • Total annual flow in the Yarra River at Banksia Street Heidelberg (Station 229135A) was 224 GL compared to the average value of 406 GL. This was the sixth successive year of below-average annual flow in the river.
  • The high rainfall during November–December 2018 had a relatively minor effect on streamflow in these rivers. The very dry soil moisture conditions across the region during the preceding winter–spring months meant much of the rainfall that occurred was soaked up by the soil.
  • In June 2019, streamflow in the Werribee River was well above average due to higher rainfall during May–June 2019 over the upper reaches of the catchment area compared to the rest of the region.