Drought
Rainfall deficiencies and water availability

Driest September on record for Australia

September rainfall was 70.8% below the 1961–1990 average for Australia, the driest September on record (since 1900). The month was dominated by high pressure systems which brought settled weather conditions and cloudless sky for most of the country.

September rainfall was below or very much below average for most of Australia. It was in the lowest 10% of historical observations for September (compared with all Septembers since 1900) for most of Victoria and New South Wales and large parts of north-eastern Tasmania, south-eastern Queensland and south-eastern, south-central and north-western South Australia extending to the adjacent parts of Western Australia. September rainfall was the lowest on record for coastal parts of Victoria's Central district and the South West Slopes district in New South Wales.

For Victoria, it was the driest September on record since observations began, with state-wide rainfall 67.1% below average. For New South Wales as a whole, September was the second-driest on record, 82.6% below average, while for South Australia it was the seventh-driest September on record.

Only small areas of Australia received above average rainfall for the month – parts of eastern Cape York Peninsula (Queensland) and the far north-east corner of the Top End (Northern Territory).

Most areas of Australia that were already experiencing rainfall deficiencies received below average September rainfall, so areas of deficiency have generally expanded and become more severe, and new areas have emerged, including along the West Coast district in South Australia, in the Central district in Victoria, part of the central east coast of Tasmania, and areas in the Top End in the Northern Territory.

For the 5-months since May 2023, areas of rainfall deficiency have developed in all states and territories, with large areas in south-west Western Australia and along much of the south-east of Australia, including smaller areas of lowest on record (since 1900) rainfall.

For the 10-month period since December 2022, there are areas or rainfall deficiency in south-west Western Australia, the south-eastern corner of Queensland and north-eastern New South Wales, and smaller areas of rainfall deficiency fringe parts of the New South Wales and Victorian coast.

The long-range forecast released on 5 October 2023 indicates for November 2023 to January 2024, that below median rainfall is likely to very likely (60% to greater than 80% chance) for much of Australia, while small areas of New South Wales, including the Upper Western, North West Slopes and Plains, and Riverina districts, and southern Queensland are more likely (60 to 80% chance) to have above median rainfall.

Significant rainfall in eastern Victoria and parts of south-east New South Wales in the first week of October is likely to ease localised rainfall and soil moisture deficiencies and will be documented in the October Drought Statement.

State of the Climate 2022 reported a shift towards drier conditions across the south-west and south-east of Australia, particularly during the cool season months of April to October. This is due to a combination of natural variability on decadal timescales and changes in large-scale circulation caused by an increase in greenhouse gas emissions. Since the 1990s, in the absence of strong 'wet' drivers, cool season (April to October) rainfall in southern Australia has generally been lower than average.

Deficiencies for the 5 months since May 2023

For the 5-months since May 2023, areas of serious (totals in the lowest 10% of periods since 1900) to severe (totals in the lowest 5% of periods since 1900) rainfall deficiency extend across a large area inland from the southern-west coast and in the Eucla district of Western Australia, along the West Coast district in South Australia, in part of the central-east coast of Tasmania, parts of south-central and eastern Victoria, along eastern New South Wales and extending inland across the northern quarter of the state, and areas in south-eastern Queensland, particularly in Wide Bay and Burnett and parts of adjoining districts, and Maranoa and Warrego districts. Much of the Northern Territory's Top End has had a drier than usual dry season (May to September), and a band of deficiencies runs from the Tiwi Islands to Groote Eylandt.

Areas of lowest on record May to September rainfall have developed in Gascoyne and Eucla districts in Western Australia, and along parts of the east coast of Victoria and New South Wales.

Since August, rainfall deficiencies have generally intensified or expanded and new deficiency areas have emerged in South Australia, south-central Victoria and part of the east coast of Tasmania.

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Deficiencies for the 10 months since December 2022

For the 10-month period since December 2022, country experiencing serious (totals in the lowest 10% of periods since 1900) or severe rainfall deficiencies (totals in the lowest 5% of periods since 1900) includes areas along the coast of Western Australia between Carnarvon and Busselton, the Eucla district, and also some inland areas in the south-west. In eastern Australia, large areas of deficiency are concentrated in the south-eastern corner of Queensland and north-eastern New South Wales. Small areas of deficiency fringe coastal New South Wales and the Victorian central and east coast, and isolated pockets occur in South Australia and south-east Tasmania.

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Soil moisture

September root-zone soil moisture (soil moisture in the top 100 cm) was below to very much below average (driest 30% of years since 1911) across most of the western and southern parts of Western Australia, much of South Australia, north and eastern Tasmania, most of Victoria and New South Wales, much of Queensland and areas in central Australia and the Top End of the Northern Territory.

Since August, soil moisture decreased across south-west Western Australia, much of South Australia, the Northern Territory, northern Tasmania, Victoria, inland New South Wales, and further inland and north in Queensland.

Evaporative stress

Evaporative stress for the 4 weeks ending 1 October 2023 is elevated (index is negative) across most of Australia away from the north, and some inland areas. Southern exceptions include parts of the south-west coast, the south-east corner of South Australia and isolated areas along The Great Divide.

Compared to last month, the evaporative stress index has increased in intensity across much of the south-east of Australia with very elevated areas south and west of the Divide, and part of the central east of Tasmania.

See the journal publication for further details on calculation and use of evaporative stress index in drought monitoring.

• For Australia as a whole, September rainfall was 70.8% below the 1961–1990 average, the driest September on record (since 1900).
• Rainfall in September was below average for most of the southern two thirds of the country.
• For the 5-months since May 2023, areas of rainfall deficiency have developed in all states and territories, with large areas in south-west Western Australia, and along much of the south-east of Australia.
• September soil moisture was below average (in the lowest 30% of all years since 1911) for much of Australia, away from the north and central inland areas.
• Low streamflows were observed mostly at sites in the south and south-eastern New South Wales, south-eastern Queensland, scattered sites in south-west of Western Australia, and most sites in Victoria and Tasmania.
• Storage levels remain low in some parts of southern and central Queensland, south-eastern parts of New South Wales, central Tasmania, and urban areas of Perth.
• For November 2023 to January 2024, below median rainfall is likely to very likely (60% to greater than 80% chance) for much of western, northern and southern Australia, with small areas of northern New South Wales having a slightly increased chance of above median rainfall.

Streamflows high in parts of the northern Australia; low in south eastern Australia and in the west of Western Australia

September streamflow conditions mostly followed rainfall patterns. Areas of average to below average rainfall and soil moisture, and subsequent low streamflow conditions, were largely concentrated in southern and south-eastern Australia, and in the south-west of Western Australia. Streamflow was average at 49% of the 575 sites across the country (based on records since 1975). Below to very much below average streamflow was observed at 40% of the 575 sites, mostly associated with below average rainfall and drier catchment conditions, particularly in the south and south-eastern New South Wales, south-eastern Queensland, scattered sites in south-west Western Australia, and most sites in Victoria and Tasmania.

In September, above to very much above average streamflow was observed at 11% of sites, mainly in northern Australia, including the Kimberley (Western Australia), Northern Territory and the north-east of Queensland's wet tropics.

Overall high storage levels across the country, but low storage levels at several locations

September had below to very much below average rainfall and soil moisture, particularly for most of Victoria and New South Wales and large parts of north-eastern Tasmania, south-eastern Queensland, South Australia and the south-west of Western Australia, resulting in a slight decrease in some storage levels from August. By the end of September, the total water storage level in Australia (across Australia's 306 public storages) was at 78.0% of capacity, slightly lower than the previous month, and higher than at the same time last year. Despite most of Australia's major storages being high, storage volumes remain low in several locations, particularly in south and central Queensland, south-eastern parts of New South Wales, central Tasmania, and urban areas of Perth.

Despite very much below average rainfall and dry catchment conditions, combined storages in the Murray–Darling Basin were 91.8% full at the end of September, a slight decrease, by 1.2%, from August, and also a decrease of 5.5% from the same time last year.

Despite average to below average rainfall and dry catchment conditions in September for most of south-west Western Australia, there was a slight increase in some storage levels. Perth's surface water storages remained low (53.2% full) at the end of September, a 1.6% increase from August, and a 7.7% decrease from the same time last year (60.9%). Long-term declines in surface water inflows to Perth's storages means the city's water supply is generally more reliant on desalination and groundwater sources.

Serious rainfall deficiencies since May, and dry catchment conditions across large parts of south-eastern Australia, including most of south-eastern Queensland, resulted in decreased volumes for many storages from last month. Water levels in the Nogoa Mackenzie system in central Queensland remain low, below half capacity (35.0% full) at the end of September but up from 22.2% at the same time last year. Water storage in Wivenhoe was slightly decreased to 67.5% full by the end of September, a decrease from same time last year (89.8%). In central Queensland, water storage in Fairbairn was below half capacity at the end of September, at 34.5%, a 2.9% decrease from August, although it was an increase from same time last year (21.2%).