Melbourne: Climate and water
- Rainfall was below-average during most of the year, which contributed to relatively low soil moisture and streamflow conditions across the region.
- Heavy rainfall associated with thunderstorm activity in December 2017 resulted in above-average streamflow in the Yarra River during that month.
For further information on the region's climate and water conditions during the 2017–18 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 streamflow 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 2017–18 year
- Total area-averaged rainfall for the year was 772 mm, below the mean value of 857 mm.
- Widespread thunderstorm activity across southeastern Australia in December 2017 contributed to well above-average rainfall across most of the region during that month.
- Rainfall in February and April 2018 was very low across the entire region. In some parts of the region, it was the driest February and April in more than 20 years.
Figure C2 Total monthly rainfall for the Melbourne region during the 2017–18 year compared with the average and percentiles for the region
- Rainfall in December 2017 was above the 90th percentile. In contrast, February and April 2018 rainfall was well below the 10th percentile.
- Most of the other months of the year experienced average to below-average rainfall conditions.
Actual evapotranspiration
Figure C3 Annual and monthly actual evapotranspiration deciles for the Melbourne region during the 2017–18 year
- Total area-averaged actual evapotranspiration was average to below average across most of the region.
- The above-average evapotranspiration during December–January is likely due to a combination of well above-average temperatures experienced across the region and increased water availability following high rainfall in December 2017.
- Below-average evapotranspiration during most of the latter half of the year (February–June 2018) may be due to the decreased water availability across the region following the very low rainfall in February and April 2018.
Soil moisture
Figure C4 Annual and monthly soil moisture deciles for the Melbourne region during the 2017–18 year
- Soil moisture in the root zone (0–1 m depth) was below average across the region.
- Rainfall and soil moisture are typically closely aligned. For example, average to above-average soil moisture conditions during the summer months (December–February) are due to the above-average rainfall that occurred during December 2017 and January 2018. Below-average soil moisture throughout the rest of the year can be attributed to the relatively poor rainfall that occurred during winter–spring 2017 and autumn 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 2017–18 year compared with average and percentiles
- Total annual streamflow in the Bunyip River was below average, reflecting the below-average rainfall conditions experienced over the catchment for most of the year.
- Streamflow in the Maribyrnong and Werribee rivers was lower than average due to a combination of upstream flow regulation and relatively poor rainfall during the year.
- Heavy rainfall associated with thunderstorm activity in December 2017, particularly over the eastern part of the region, resulted in above-average streamflow in the Yarra and Bunyip rivers during that month.