National Water Account 2017

Perth: Climate and water

A wetter start than the previous year, and unusually high rainfall in January–February, led to the highest annual rainfall in three years. Streamflow increased from the previous year and high flows in the Swan and Murray rivers followed the unseasonal summer rain.

For further information on the region's climate and water conditions during the 2016–17 year scroll down this page or click on the links below:


 About the region

The Perth region lies within southwestern Australia, which generally experiences dry, hot summers and wet, mild winters. Most of the rainfall in the region occurs during a 5-month period from May–September. The seasonal flow characteristics of the region's rivers reflect the distribution of rainfall over the year. Most of the streamflow and storage inflows occur during the winter and early spring months (June–October), and usually very little streamflow and storage inflow occurs during summer and autumn (December–May).


Climate conditions


Figure C1 Annual and monthly rainfall deciles for the Perth region during the 2016–17 year


  • Total area-averaged rainfall across the region was 696 mm compared to the long-term average of 788 mm.
  • In the first five months of the year, the climate was influenced by a negative Indian Ocean Dipole phase which is associated with higher winter–spring rainfall and cooler temperatures in the region. Rainfall in this period was about 30% higher than the previous year. 
  • In late January and early February, atmospheric moisture from tropical lows in the north of Western Australia brought unusually high rainfall to the region, resulting in the wettest summer on record at a number of stations (see Special Climate Statement 60 for more detail).
  • In autumn, warmer tropical Pacific Ocean temperatures and a cooler eastern Indian Ocean led to fewer cold fronts and low pressure systems crossing the region. This resulted in much below average rainfall, especially in April when the rainfall was 1 mm.

Figure C2 Total monthly rainfall for the Perth region during the 2016–17 year compared with the long-term average and percentiles for the region


  • February rainfall was nine times the average for that month and total summer rainfall (December–February) was four times the average for that 3-month period. 
  • Most of the summer rain fell during two 3–4 day periods: late January in which the rain occurred over much of the northern half of the region; and early February in which rain was extensive across the region.
  • Rainfall for the 3-month period from April–June was the second lowest on record and many stations in the region recorded zero rainfall for April. The Perth Metro station recorded its fourth rain-free April since 1876.



Figure C3 Annual and monthly actual evapotranspiration for the Perth region during the 2016–17 year


  • Total area-averaged actual evapotranspiration was 642 mm for 2016–17, slightly lower than the average value of 676 mm.
  • Evapotranspiration was below average across most of the region in the first half of the year, reflecting near-average rainfall combined with below average temperatures related to the negative Indian Ocean Dipole phase.
  • The high rainfall In late January–early February increased water availability and evapotranspiration rose to the extent that it was the highest on record in the north of the region. It remained high in March and declined in subsequent months as soil moisture declined during the dry autumn.


Figure C4 Total monthly actual evapotranspiration for the Perth region during the 2016–17 year compared with the long-term average and percentiles for the region


  • Evapotranspiration was below average in all months except for February and March when higher water availability contributed to very much above average evapotranspiration.


Soil moisture

Figure C5 Annual and monthly soil moisture deciles in the root zone (0–1 m depth) for the Perth region during the 2016–17 year


  • The seasonal distribution of soil moisture in the root zone (0–1 m depth) reflected the rainfall pattern, with close to average soil moisture for the first half of the year followed by above average soil moisture in summer, related to the high summer rainfall.  
  • Very much below-average rainfall in the latter part of the year led to drying and below-average soil moisture during this period.
  • More information on soil moisture distribution across the Perth region is available in the Australian Landscape Water Balance.


Streamflow responses

 Figure C6 Key flow gauging stations along the main rivers within the Perth region

Figure C6 Key flow gauging stations along the main rivers within the Perth region


  • The Swan, Murray and Harvey rivers are the largest rivers in the region. The Swan River's catchment extends to the east of the Perth region where the river is known as the Avon River, while the Murray and Harvey river catchments lie completely within the Perth region.

Figure C7 Total monthly flow for key Perth region rivers compared to long-term average and percentiles


  • In the first half of the year, streamflow in the region was below average but almost four times higher than the previous year reflecting the improved rainfall conditions.
  • Following the unusually high rainfall in the region in late January–early February, both the Swan and Murray rivers experienced their highest February monthly flows on record. The Swan River also had its highest flow in any month since July 1995.  
  • Despite the significant response in the Swan and Murray rivers, the January–February rainfall generated little flow in the rivers feeding into storages, including the Harvey River, reflecting differences in catchment characteristics and the spatial distribution of the rainfall.
  • River flow in the latter part of the year from April to June was below average and mostly lower than the previous year due to the very dry autumn.


Major water reforms

Groundwater Replenishment Scheme


Advanced Water Recycling Plant, part of the Groundwater Replenishment Scheme at Beenyup

  • To secure the region's water supply in the face of large declines in inflows to Perth urban water storages since the 1970s, the state government has pursued intiatives including desalination and managed aquifer recharge.
  • In 2013, following a successful three year trial, the government initiated the development of Stage 1 of Perth's Groundwater Replenishment Scheme. The scheme includes injection of treated wastewater to Perth's confined aquifers at Beenyup in Perth's north.
  • Stage 1 is designed to inject 14 GL/year to a borefield in the Yarragadee and Leederville aquifers near the Beenyup wastewater plant and started operation in late 2017.
  • Stage 2, providing another 14 GL/year of injection, was announced in July 2016, received Environmental Protection Authority approval in May 2017 and is due to be commissioned in December 2018. 
  • For more information refer to the Water Corporation webpage.


Harvey Water irrigation expansion


Figure C8 Proposed expansion of the Harvey Water irrigation area

Figure C8 Proposed expansion of the Harvey Water irrigation area


  • Harvey Water is participating with Collie Water in the development of the Myalup-Wellington project.
  • Amongst its aims is arresting and reversing the increased salinity in Wellington Reservoir. Wellington Resevoir is the second largest surface water storage in Western Australia and salinity levels are currently recorded at about 1,200 mg/L.
  • As part of the project, the open channels in the Collie River Irrigation District will be replaced with gravity pressure pipes.
  • The water saved by piping the Collie River district will be used to expand production at the Myalup precinct.
  • The project received a commitment of partial funding from the state government in January 2017 and was designated a Priority Project by Infrastructure Australia in November 2017.
  • For further information refer to the Western Australian Government’s Water for Food website.