Perth: Climate and water

  • Total annual rainfall for the 2021-22 year was below average for the fourth consecutive year, with November to March being exceptionally dry.
  • Streamflows were above average during late-winter and early-spring, however, a lack of rainfall resulted in below-average streamflows from November onwards.
  • Groundwater levels at 30 June 2022 were slightly lower than this time last year.

Schematic representation of the Perth region. In 2021–22, rainfall was 782 mm, less than average for the fourth consecutive year. Streamflow in Swan River in 2021–22 was 571 GL compared to the average value of 281 GL. Groundwater levels were slightly lower than last year.

For further information on the region's climate and water conditions during the 2021-22 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, with most of the streamflow and natural storage inflows occurring during the winter and early spring months (June–October).

 

Climate conditions

Rainfall

Figure C1 Annual and monthly rainfall deciles for the Perth region during the 2021–22 year

  • Total area-averaged rainfall for the 2021-22 year was 782 mm, slightly less than the mean value of 794 mm.
  • Heavy rain, associated with a cold front and cut-off low, impacted the region during July 2021, producing the seventh wettest July on record, and wettest July since 1996.
  • October 2021 was the ninth wettest October on record.
  • From November 2021 to April 2022, rainfall was very much below average, with the region only receiving 58% of the average for this period.
  • Rainfall was above average for both May and June, helping top up storages by the end of the 2021-22 year.

 

Figure C2 Total monthly rainfall for the Perth region during the 2021–22 year compared with the average and percentiles for the region

  • Rainfall was above the 90th percentile in July 2021 and October 2021, with the region recording its seventh wettest July and ninth wettest October on record.
  • From November 2021 to March 2022, the region only received 39% of the average rainfall for this period, with January 2022 being the seventh driest January on record.
  • All other months ranked between the 10th and 90th percentiles.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Perth region during the 2021–22 year

  • Total area-averaged actual evapotranspiration was average across the region during the 2021-22 year.
  • Evapotranspiration was below average across most of the region during January–March 2022 due to low water availability during a dry summer.
  • Evapotranspiration was predominantly above average from July–September 2021 due to increased water availability during a wet winter period.
  • Evapotransipiration was average to above to average in mid-spring and mid-autumn. The exception was in October, where evapotranspiration was average, despite the well above average rainfall.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Perth region during the 2021–22 year

  • Soil moisture in the root zone (0–1 m depth) was average to below average across most of the region during the 2021-22 year.
  • Soil moisture was well below average over most of the region during December 2021 and January–February 2022 during a dry summer.
  • During mid winter to spring, particularly in July–August 2021 and October–November 2021, soil moisture was avearge to above average over most of the region following rainfall in July 2021; however, in September 2021, soil moisture was average to below-average conditions.
  • More information on soil moisture distribution across the Perth region is available in the Australian Water Outlook.

 

Hydrological responses

Streamflow

Map of key gauging stations. Swan River at Walyunga, station number 616011, is in the northern part of the region about 40 km upstream of Perth. Murray River at Baden Powell Water Spout, station number 614006, is on the Darling Range in the region's south. Harvey River at Clifton Park, station number 613052, is in the southern part of the region on the coastal plain.
Figure C5 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.
  • The Swan and Murray rivers are unregulated whereas the Harvey River is regulated by Harvey Dam.

 

Figure C6 Total monthly flow for major rivers in the Perth region during the 2021–22 year compared with the average and percentiles

  • Though rainfall over summer and autumn was exceptionally low, annual streamflow in the region's major rivers were above average during the 2021-22 year, reflecting the wet conditions in late-winter and early-spring. 
  • From July to September 2021, streamflows were above average following the seventh wettest July on record, with all sites peaking above the 90th percentile in either July 2021 or August 2021.
  • Following a lack of significant rainfall, streamflows dropped below average in late-spring and remained low through to June 2022. The Swan River at Walyunga (Station 616011) ceased to flow throughout February and March.

 

Groundwater levels

  • The Perth region includes a number of important aquifers. The shallow Superficial Aquifer is an important source of public and self-supply and also supports numerous groundwater-dependent ecosystems in the Gnangara and Jandakot mounds. The deeper confined aquifers (e.g. Leederville and Yarragadee) are major sources of urban water supply.

 

Figure C7 Groundwater levels for key bores within the Perth region from 2010–2022

  • Groundwater levels in Perth's aquifers during the 2021-22 year were slightly higher compared to the historical average, with the improved rainfall conditions during the previous two years leading to an increase in water levels since 2016 in both the Gnangara and Jandakot mounds.
  • Groundwater levels in Perth's aquifers were slightly higher compared to the historical average, the improved rainfall conditions during the previous two years have led to an increase in water levels since 2016 in both the Gnangara and Jandakot mounds.
  • Average winter rainfall in 2021–22 resulted in recharge to the surficial aquifers of the Gnangara Mound which was an improvement from the previous two years of low winter rainfall which resulted in low groundwater recharge and low groundwater levels.
  • The rising trend has been influenced by efforts to reduce and redistribute groundwater extraction.
  • Groundwater levels in the confined aquifers that are separated from the surface by aquitards (low permeability shale and clay layers) remain low compared to the average. Fluctuations in these aquifers are related more to usage than climate.