Drought
Rainfall deficiencies and water availability

Long-term rainfall deficiencies persist; some soil moisture recovery in the southeast

After relatively good rainfall in the January to April period, May 2020 was a dry month for much of Australia. Rainfall for the month was below average for much of the southern half of the mainland, extending into large parts of the southern half of Queensland, and much of the eastern half of Tasmania. Northern Australia, which is now in its traditional dry season, experienced above average falls, though total amounts were light away from the Kimberly and northwest interior of Western Australia and Queensland's east coast.

The size of the rainfall deficit accumulated over annual and longer timescales prior to 2020 remains very large over much of Australia. Despite above average January to May rainfall for much of southeastern Australia and parts of the northwest and Northern Territory, serious or severe longer-term rainfall deficiencies persist over very large areas.

Additional widespread above average rainfall is needed to lift areas out of deficiency at annual and longer timescales and provide relief from the impacts of this long period of low rainfall (such as renewing water storages).

The Bureau of Meteorology also monitors rainfall deficiencies and impacts on water resources on longer timescales such as the current severe multi-year drought affecting large parts of eastern Australia. This is discussed further below, and we have Special Climate Statements on this long dry period.

Autumn (March–May) rainfall was very much below average over large areas in the southwestern third of Western Australia and in southeastern Queensland. Although no shorter period is currently included in the Drought Statement monitoring, rainfall deficiency maps are available for standard periods.

The role of climate change in rainfall reduction over southern Australia and along the Great Dividing Range is discussed in State of the Climate 2018 which shows that parts of southwest, southeast and eastern Australia, including parts of southeast Queensland and southern and eastern New South Wales, have seen substantial declines in cool season rainfall in recent decades.

The Climate Outlook for June to August, issued 4 June, indicates an increased chance of wetter than average conditions in parts of South Australia, northern and western New South Wales, and southern Queensland. Winter rainfall is likely to be below average for coastal southeast South Australia, southwest Victoria, and most of Tasmania.

The current set-up of large-scale climate drivers heading into winter is quite different than at the same point in 2018 or 2019. The Bureau will continue to closely monitor the observed conditions and outlooks over the coming months, and report on the implications for rainfall deficiencies, soil moisture, and water storage.

26-month rainfall deficiencies

Rainfall deficiencies at the 26-month timescale, from April 2018 to May 2020, have been removed from much of the Kimberley and north of the Interior District in Western Australia following very much above average May rainfall over much of the north of Western Australia. However, deficiencies persist in the northern tip of the Kimberley.

Rainfall deficiencies have generally increased over the remainder of the affected areas of Australia at this timescale, compared to those for the 25 months ending April 2020. The depth of rainfall anomalies over this period is very great, in excess of 400 mm below average for the period over large areas of the east and north. It will take several further significant rainfall events to turn around those long-term deficiencies.

Serious to severe rainfall deficiencies are in place for the 26-month period across much of the South West Land Division and along the south coast of Western Australia, parts of the western Pilbara and northern tip of the Kimberley, the east of the Interior District, and pockets throughout the inland areas of the State; large areas of the Northern Territory away from the east; much of South Australia; the southeastern quarter of Queensland; much of New South Wales except areas of the northeast coast and central coast, and a broad band through the central west from around Griffith to the Queensland border north of Bourke; and across eastern Victoria and the northwest and parts of the northeast of that State.

The area of lowest on record rainfall for the 26-month period has increased month-on-month. These include along the border of New South Wales and South Australia, along the New South Wales–Queensland border and in parts of southeast Queensland, and a large area on the southern coast of Western Australia.

Extended dry conditions over eastern Australia

Rainfall deficiencies have affected most of the New South Wales, Queensland and South Australian parts of the Murray–Darling Basin since early 2017, as detailed in the last update on the long-running dry and for 2019 in the Annual Climate Statement. These longer-term deficiencies also extended to parts of the New South Wales coast, particularly in the Hunter and Illawarra to southeastern districts, and to much of the eastern half of South Australia from Adelaide northwards. The deficiencies were most extreme in the northern Murray–Darling Basin, especially in the northern half of New South Wales and adjacent southern Queensland, where areas of lowest on record rainfall are extensive. Some of the largest rainfall deficiencies occurred in the upper catchments of some of the major tributaries of the Darling, including the Macquarie, the Namoi–Peel, and the Border Rivers.

A wetter than average first five months of 2020 has eased the severity of short-term deficiencies over much of eastern Australia and has provided a better start to the winter cropping season in many regions. The impact of below average rainfall over the longer term is still evident in water resources, especially in northern parts of the Murray–Darling Basin.

Significant deficiencies remain at long-term timescales across many parts of the country. Averaged over the Murray–Darling Basin, the 36 months from June 2017 to May 2020 has been the driest such period on record. For New South Wales it has been the second-driest such period on record, behind June 1900 to May 1903, spanning the Federation Drought. Other areas affected by longer-term rainfall deficiencies include eastern Victoria, eastern and northern Tasmania, eastern South Australia except for the southeast, and some parts of southwest Western Australia.

The dry conditions of the last three years were particularly acute during the cool season, which is important in many regions for generating runoff. April−October rainfall totalled across the three years was the lowest on record across large parts of western and eastern New South Wales. All three years had seasonal rainfall below 200 mm for New South Wales, with 2018 and 2019 both below 150 mm; there is no previous instance of two consecutive years below 150 mm, or three consecutive years below 200 mm.

Rainfall in the first five months of 2020 has improved flows in parts of the Basin but total storages are still low, especially in the north (see Water section of this Statement). This year has seen the first April–May period with close to average rainfall for New South Wales and the Murray–Darling Basin since 2016.

Water storages start to fill in the southern Murray–Darling Basin but levels remain low in the north.

Water storage levels increased slightly in most of the major storages in the Murray–Darling Basin, taking the total storage to 40%, an increase of 5% since last month and 7% since the same time last year.

Major storage levels remain low in the northern Murray–Darling Basin. Current total water storage in the northern Basin remains at only 18% of capacity, an increase of 0.7% since last month. Most of the northern storage levels had little change in May with Burrendong storage in the Macquarie Valley seeing the largest increase of 4%. Many of the northern basin catchments have experienced prolonged dry conditions and significant follow up rainfall is still needed to replenish these water storages. However, the soils in the catchments of many of these storages are still wet enough, that any follow-up rain, will be likely to produce runoff and inflows to the storages.

The water that made its way down the Darling River has continued to fill the Menindee Lakes system with the total storage reaching 28% (47 000 ML), an increase of 9% since last month. The water has moved through the system from Lake Wetherell to Lake Pamamaroo but has not yet started filling Lake Cawndilla or Menindee Lakes.

The total storage in the southern Basin increased during May with the start of the winter filling season. Total storage increased by 6% to 45% of capacity, which is 7% higher than May 2019. All three of the very large storages in the southern Basin (Hume, Dartmouth, and Eildon) increased this month, with Hume increasing by 13% (376 353 ML) to 26% full. Lake Victoria, on the Murray upstream of the South Australian border, also increased by 20% in May. The past three filling seasons have seen insufficient inflows to replenish the seasonal drawdown.

Rivers levels drop during May in the northern Murray–Darling Basin

The monthly average river flows in the northern Basin were near average for May. However, many of these rivers decreased from higher flows at the beginning of the month to almost no flow by the end of May. In the northeastern tributaries of the Murray–Darling Basin, where major flows were seen in early 2020, the monthly average flows have now dropped to very much below average.

Upstream sections of far northern rivers, such as the Condamine and Balonne, did not flow at all during May while other major rivers, such as the Namoi, ceased to flow in sections by the end of May. Many of these rivers are highly regulated and are unlikely to return to sustained flow without significant increases in the major water storage levels in the headwaters of the catchments.

Minor flows are being maintained down most of the Darling River but the peak flows seen in March and April are now making their way into the Menindee Lakes system. Some minor flows are still being released to the Lower Darling, maintaining the connectivity with the Murray River.

The majority of the southern Basin rivers are running at near-average flows for May. The exceptions are the Murray River and the upper tributaries of the Lachlan and Murrumbidgee rivers which are all at very much above average flow. The high flows in the Murrumbidgee and Lachlan rivers are above the major storages of Wyangala and Burrinjuck respectively and will provide valuable inflows into these storages in the coming months.

The rain since February has led to significant flows in the upper Murray River with record highs for May occurring at Jingellic, upstream of Hume Dam. These high flows were reflected in the increases observed in the Hume water storage level at the end of May. Very much above average flows were also observed down through the Yarrawonga weir and Barmah Forest. These higher than average flows were due primarily to natural inflows as the major storages made minimal releases during May.

Soil moisture

After a drier than average May across much of the southern half of Australia, root-zone soil moisture (in the top 100 cm) has decreased through May across the southern half of Western Australia, Central Australia, the Top End, and southern Queensland, compared to April.

Soils were drier than average for the month across the southwestern half of Western Australia; a large area of the southern Northern Territory and adjacent far northern South Australia; much of the Top End; areas of inland Queensland, coastal southeast Queensland, and parts of northern Cape York Peninsula; far eastern Victoria and far southwestern New South Wales.

For large areas of the southwestern half of Western Australia root-zone soil moisture for May was very much below average (in the lowest 10% of historical observations).

Soil moisture has increased across parts of northern Australia, and southeastern South Australia. Soil moisture remains above average for much of southeastern Australia.

Soil moisture for May was above average over most of New South Wales and Victoria except along the east coast and in northwestern New South Wales; for southeastern South Australia and the Eyre Peninsula; most of Tasmania; the western Kimberley; and scattered pockets through the inland regions of tropical northern Australia.

Despite rainfall for January to May 2020 being above average for large areas of southeastern and northwestern Australia, the influence of very low rainfall over longer timescales is still evident in the 12-month soil moisture for June 2019–May 2020, which was very much below average over very large areas of Australia.

Soil moisture remains above average across the Murray–Darling Basin

The root-zone soil moisture in the Murray–Darling Basin was average to very much above average across most of the Basin. Despite decreases in root-zone soil moisture levels during May, the monthly average remained above to very much above average across most of the central and southern Basin. The soil moisture levels in catchments such as the Lachlan and Macquarie Rivers in central New South Wales were very high at the start of May, following significant rain at the end of April. By the end of May, these catchments had decreased by 10–20% soil available water, but remain above average for this time of year.

The soil moisture in the Victorian Alpine regions, where the catchments of the very large storages in the southern Basin lie, remain very much above average, priming them for runoff during the southern winter filling season.

• Rainfall deficiencies around the 9-month period have been removed from most of Australia, and the period starting August 2019 is no longer being formally monitored within the Drought Statement
• Rainfall was below average for much of the southern half of Australia during May; and was above average for much of northern Australia, particularly in the Kimberley and central northern Queensland
• Short-term rainfall deficits exist in parts of Australia—particularly widespread in the southwestern third of Western Australia and southeastern Queensland where recent rainfall has been below average
• Average to above average January–May rainfall has led to soil moisture recovery in much of southeastern Australia over timescales out to 5-months duration
• Compared to April, monthly soil moisture has decreased across the southern half of Western Australia, Central Australia, the Top End, and southern Queensland; root-zone soil moisture for May was very much below average for much of the southwestern third of Western Australia
• Monthly soil moisture has increased across parts of northern Australia, southeastern South Australia, and remains above average for much of the southeast and Murray–Darling Basin
• At the 26-month timescale (i.e. since April 2018) rainfall deficiencies have decreased across much of the Kimberley, but have increased across much of southern Australia
• Accumulated rainfall deficit at longer timescales—such for the 26-month period since April 2018—are significant in many parts of Australia, and may persist for some time
• Water storage levels in the northern Murray–Darling Basin remain low despite recent rainfall; river flows in the northern Murray–Darling Basin dropped during May, and dried out in the far north
• Across Australia the effect of low rainfall over 2018 and 2019 continues to be felt in many large water storages
• The Murray River received valuable inflows from local and headwater catchments, increasing storage levels and river volumes
• Recent above average rainfall contrasts sharply with the situation at the same time of year in 2018 or 2019; the Bureau will continue to closely monitor short-term or potential emerging deficiencies as the southern wet season continues