Perth: Climate and water
For the water account period 01 July 2022 - 30 June 2023
- Total annual rainfall for the 2022-23 year was below average for the fifth-consecutive year, with the region experiencing is twelfth-driest summer on record.
- Soil moisture in the root zone (0-1 m depth) was close to average for most of the region, with a few areas of below-average soil moisture, reflecting the region's rainfall.
- Total annual flows in the Harvey River and Murray River were below average, while streamflows in the Swan River were above average.
- By 30 June 2023, groundwater levels in the region's Superficial Aquifers were slightly higher than the start of the 2022-23 year, while the Leederville Aquifer increased by over two metres.
For further information on the region's climate and water conditions during the 2022-23 year scroll down this page or click on the links below:
About the region
- The Perth region has a hot-summer Mediterranean climate, characterised by warm to hot dry dummer, and cool to mild wet winters.
- Around 80% of the region's rainfall occurs from late-autumn to mid-spring (May to October), mainly due to cold front and low-pressure troughs that sweep across the region during this time of year. Rainfall from late-spring to mid-autumn (November to April) is typically low, with the occasional month going without any rainfall.
- Streamflows in the region's rivers generally reflects the distribution of rainfall throughout the year, with most of the streamflows and storage inflows occurring during the winter and early-spring months (June to October). Throughout summer and into autumn (December to April), streamflows can cease to flow.
Climate conditions
Rainfall
Figure C1 Annual and monthly rainfall deciles for the Perth region during the 2022–23 year
- Total area-averaged rainfall for the 2022-23 year was 722mm, 9% below the mean value of 794mm. This was the region's fifth-consecutive year of below-average rainfall, reflecting the drying trend due to underlying background changes to the region's climate.
- Rainfall throughout winter, the region's wettest period, was 8% below average despite above-average rainfall occurring during August 2022.
- A cold front interacting with a moisture-laden cloud band brought heavy rain to the region during August 2022, resulting in the region's twentieth-wettest August on record. Some sites to the north registered their highest August daily total on record.
- Throughout spring, a lack of cold fronts resulted in below-average spring rainfall, although, rainfall during November 2022 was close to average.
- Even though summer is the driest period for the region, rainfall during the 2022-23 summer was particularly low, with the region experiencing its twelfth-driest summer on record. This included the region's fourth-driest February on record, where little rainfall occurred.
- During the first two months of autumn (March 2023 and April 2023), rainfall was almost double the monthly averages due to low-pressure systems bringing high rainfall to the region, with March 2023 being the region's fifteenth-wettest March and April 2023 being the region's twelfth-wettest April on record.
- Typically, the frequency of rainfall in the region increases during May, however, rainfall during May 2023 was very much below average, with the region having its fifth-driest May on record.
- In June 2023, the passage of several cold fronts resulted in rainfall being slightly below average, but brought much-needed rain to the region leading into winter.
- More information on Australia's climate and water over the 2022-23 year can be found at: Financial year climate and water statement 2022-23.
Figure C2 Total monthly rainfall for the Perth region during the 2022–23 year compared with the average and percentiles for the region
- April 2023 was the only month to record rainfall above the 90th percentile, however, rainfall during August 2022 and March 2023 was just under the 90th percentile.
- Rainfall from September 2022 to February 2023 was either average or below average, with little rainfall occurring in February 2023, resulting in it ranking below the 10th percentile.
- May 2023 ranked below the 10th percentile, following the region's fifth-driest May on record, with about a quarter of the long-term average falling across the region.
Actual evapotranspiration
Figure C3 Annual and monthly actual evapotranspiration deciles for the Perth region during the 2022–23 year
- Total area-averaged actual evapotranspiration for the 2022-23 year was average to below average across the region, following the region's fifth-consecutive year of below-average rainfall, reducing the amount of water available in the region.
- During July 2022, evapotranspiration was predominantly average across the region, despite below-average rainfall during the previous few months (May to July 2022). Evapotranspiration along parts of the western coastline were below average, while areas of above-average evapotranspiration were more prominent in the northeast and southeast.
- Despite August 2022 being the region's twentieth-wettest August on record, evapotranspiration was predominantly average, with pockets of below-average and above-average evapotranspiration scattered throughout the region, following months of below-average rainfall, reducing the amount of surface water available.
- In the last two months of spring, evapotranspiration was average to below average, and remained average to below average through to March 2023, following the region's twelfth-driest summer on record, further reducing the amount of water available in the region.
- Following the region's fifteenth-wettest March and twelfth-wettest April, evapotranspiration bounced back to being predominantly above average across the region during April 2023.
- The effect of the increase in this water availability carried over into May 2023, where evapotranspiration was predominantly average to above average despite the region suffering its fifth-driest May on record.
- By June 2023, following the lack of rainfall in the previous month, evapotranspiration was average to below average across most of the region.
Soil moisture
Figure C4 Annual and monthly soil moisture deciles for the Perth region during the 2022–23 year
- Soil moisture in the root zone (0–1 m depth) for the 2022-23 year was close to average for most of the region, with a few areas of below-average soil moisture, reflecting the region's rainfall, which was slightly below average.
- Despite winter being the wettest time of the year for the region, the soil moisture during July 2022 was predominantly below average following below-average rainfall during the previous few months.
- Following the region's twentieth-wettest August on record, the soil moisture rebounded to being predominantly above average across the region during August 2022, with parts of the north having their highest August soil moisture on record.
- Throughout spring, the soil moisture returned to near-average levels, except for October 2022, where the soil moisture was below average across most of the region.
- The soil moisture diminished rapidly during January and February, following the region's twelfth-driest summer on record, with soil moisture being very much below average across most of the region at the end of summer.
- Although, rainfall during the first two months of autumn (March 2023 and April 2023) was almost double the monthly averages, the lack of rainfall throughout summer resulted in the soil moisture taking until April 2023 to reflect the recent rainfall.
- However, this increase in soil moisture was short lived following the region's fifth-driest May on record, resulting in the soil moisture being average to below average, except for southern parts of the region, where the soil moisture remained above average.
- By June 2023, the soil moisture was near average for most of the region, despite below-average rainfall over the last two months of the 2022-23 year.
- More information on soil moisture distribution across the Perth region is available in the Australian Water Outlook.
Hydrological responses
Streamflow
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 2022–23 year compared with the average and percentiles
- Total annual flows in the region's major rivers for the 2022-23 year was below average in the Harvey River and Murray River, but above average in the Swan River, reflecting the fifth-consecutive year of below-average rainfall. For the Swan River at Walyunga (Station 616011), the total annual flows were 467 GL compared to the average annual flow volume of 285 GL.
- Streamflows typically peak in flows during late winter, and following the region's twentieth-wettest year on record, all streamflows reached their highest flow volumes in August 2022. However, only the Swan River at Walyunga peaked above the 90th percentile and remained above the 90th percentile in September 2022.
- Following a decline in rainfall over spring, streamflows also decreased in flow volumes, which is typical for this time of year, with streamflows in the Harvey River at Forrest Highway (Station 613036) in particular, falling to flow volumes near or below the 10th percentile.
- Throughout summer, streamflows at all sites remained low, with streamflows in the Swan River at Walyunga ceasing to flow during February 2023.
- There was a slight rise in streamflows during the first two months of autumn, with the Swan River at Walyunga and the Murray River at Baden Powell (Station 614006) peaking above the 90th percentile in April 2023, after the experienced its fifteenth-wettest March and twelfth-wettest April on record.
- In May 2023, all streamflows decreased in flow volumes, following the region's fifth-driest May on record, with streamflows in the Harvey River at Forrest Highway dropping below the 10th percentile. Following near-average rainfall in June 2023, streamflows begun increasing in flows again, leading into winter, where streamflows are at their highest.
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 2010–2023
- Groundwater levels in Perth's aquifers at the end of the 2022-23 year were lower than the historical average, but higher compared to the same point last year, with the improved groundwater levels a combination of rainfall being closer to average over the last few years, as well as continued efforts to reduce and redistribute groundwater extractions.
- Groundwater levels in the confined aquifers (Leederville and Yarragadee) 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 urban water usage than climate.
- Following the region's twentieth-wettest August on record, all groundwater aquifers increased throughout August and into spring, due to increased recharge, peaking in October 2022.
- The region's twelfth-driest summer on record, which included the fourth-driest February, resulted in groundwater levels decreased in both superficial aquifers throughout summer, with the Jandakot Superficial Aquifer reaching its lowest levels by the end of summer.
- However, following the region's fifteenth-wettest March on record, the Jandakot Superficial Aquifer rebounded by 1.5m during March 2023.
- Despite the above-average rainfall during the first two months of autumn, the Gnangara Mound Superficial Aquifer continued to slowly decrease throughout autumn, while the Jandakot Superficial Aquifer also decreased during the back half of autumn.
- By 30 June 2023, the superficial aquifers finished up to 30cm higher than the start of the 2022-23 year, while the Leederville Aquifer finished 2.78m higher compared to its groundwater levels at the beginning of the 2022-23 year.
- More information on Perth's groundwater resources can be found in the Region description.
Note: Groundwater data for the Leederville Aquifer was only available up to November 2022.