Drought
Rainfall deficiencies and water availability

A wet April in the southeast helps ease rainfall deficiencies in some areas

Rainfall during April 2020 has been above average across much of the southeast, and for Victoria it was the third-wettest April on record. However, the size of the rainfall deficit accumulated over annual and longer timescales prior to 2020 is very large over much of Australia. This means recent above average rainfall has not yet made up for this shortfall, and serious or severe rainfall deficiencies persists over very large areas at these longer timescales.

Additional widespread, above average rainfall is still 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.

The role of climate change in rainfall reduction over southern Australia is discussed in State of the Climate 2018 which shows that parts of southwest Australia, and large parts of 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 May to July, issued 30 April, indicates an increased chance of wetter than average conditions for most of Australia. The north and east coast have roughly equal chances of wetter or drier conditions.

9-month rainfall deficiencies

Rainfall deficiencies at the 9-month timescale, from August 2019 to April 2020, have decreased across most affected areas of Australia following above average rainfall across large areas during March and April. The progress of ex-tropical cyclone Esther in early March contributed to above average rainfall in an arc from the inland Kimberley in the northwest to the southeast of Australia in March, whilst above average rainfall from vigorous cold fronts across the southeast in April further eased deficiencies in parts of the region. If deficiencies ease further in May this period will be no longer be formally monitored within the Drought Statement although rainfall decile and deficiency maps will continue to be produced for standard periods.

Serious to severe rainfall deficiencies still persist in several parts of the country: in small areas along the border of South Australia and New South Wales, in northwest South Australia and the southwest of the Northern Territory; a small region spanning far eastern Victoria into southeastern New South Wales; parts of the south coast, southwest and west coast of Western Australia; an area in the central to northeastern Top End in the Northern Territory and parts of the far northern Kimberley; and areas of eastern Queensland, including the inland southeast.

25-month rainfall deficiencies

Rainfall deficiencies for the period from April 2018 to April 2020 have eased slightly in severity and extent across most of Australia, especially across southeastern parts of New South Wales, compared to those for the 24 months ending March 2020. However, the depth of the 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 25-month period across much of the South West Land Division in Western Australia, parts of the Kimberley and the northeastern Interior District, and parts of the western Pilbara; large areas of the Northern Territory away from the east; much of South Australia; the southeastern quarter of Queensland; most of far western and northeastern New South Wales and much of the southeast of that State; across northwest Victoria and the far-east of that State.

While the area of lowest on record rainfall for the period has again reduced month-on-month, areas of record low rainfall for the 25-month period persist along the border of New South Wales and South Australia, in areas along the New South Wales–Queensland border, in parts of the southern coast of the South West Land Division and South Coastal District in Western Australia, and scattered pockets elsewhere.

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 extended across large areas. 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 start to 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. However, the rainfall deficiencies were severe over an extended period so recovery will be a slow process. The impact on water resources is still evident, especially in northern parts of the Murray–Darling Basin. Significant deficiencies remaining at long-term timescales across many parts of the country. Averaged over the Murray–Darling Basin and New South Wales, the 36 months from May 2017 to April 2020 has been the second-driest such period on record, behind May 1900 to April 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. The very much below average November and December rainfall in 2019 over most of the main water catchments of New South Wales and the Murray–Darling Basin as a whole has further exacerbated the effect of low inflows to date. Rainfall in the first four months of 2020 rainfall has improved flows in parts of the Basin but total storages are still low, especially in the northern Basin (see Water section of this Statement).

Water storage levels remain low in the Murray–Darling Basin

Water storage levels increased slightly in most of the major storages in the Murray–Darling Basin, taking the total storage to 35%, an increase of 3% since last month and 1.5% since the same time last year.

The total storage in the northern Basin increased by 3.4% in April and is now 5.8% higher than the same time last year. Increases in April were primarily driven by inflows to Burrendong and Windamere storages in the Macquarie Valley. Current levels in the Northern Basin remain at only 17% of capacity, less than 2% higher than the storage levels in 2009, at the height of the Millennium drought in the north. Many of the northern basin catchments have experienced prolonged dry conditions on multi-year timescales and significant follow-up rainfall is still needed to replenish water storages.

The total storage in the southern Basin increased by 3.4% to 40.5% of capacity. Some of the smaller storages in the southern catchments including Lake William–Hovell increased by up to 30% but the minor increases in the larger storages such as Lake Victoria, Eppalock, Blowering, and the Menindee Lakes drove the total storage increase in April.

Bulk downriver releases ceased in April and inflows increased with higher than average rain in the upper catchments of the Murray River. This resulted in the levels in the very large storages of Hume, Dartmouth, and Eildon showing slight increases.

Water in the Lower Darling River reaches the Murray River

The river flows generated in February and March in the northern Murray–Darling Basin rivers have continued to make their way down the Darling River system during April.

The flow in the Darling River at Bourke is above average for April, compared to the past 40 years, and is still flowing into the Menindee Lakes. The water released from the Menindee Lakes into the Lower Darling River in late March joined the Murray River water near Wentworth on the 12th of April. This is the first significant flow in the Lower Darling River since January 2018 and an important event for local communities.

Following the limited April rain and the drying of the soil, the catchments in the far northern Basin have started to dry out and the ephemeral rivers that flow from them have started to recede. The upper reaches of the Condamine and Warrego rivers have stopped flowing. In contrast the Macquarie River is still delivering significant volumes of water into the Darling River system.

Despite recent rain in the southern Basin, flow in most of the rivers remain average to lowest on record since 1980. A significant proportion of the rain went to the increases seen in soil moisture in the catchments. Bulk water releases ceased in April and, while allocations were low this season, the delivery of water contributed to the flow recorded in the Murray River. The Murray River above Hume Dam did record very much above average flow for April, but the majority of this water will likely be retained in Lake Hume for future needs.

Urban water storages

Monsoon provides valuable recharge to groundwater around Darwin

The Darwin surface water storage levels increased slightly during April to 69.5% of capacity, which is still 6% lower than this time last year. This represents a 17% increase this wet season compared to only 5% in the 2018/19 wet season. With 1 May signalling the end of the northern Australia wet season, storages are unlikely to receive significant surface water inflows until next wet season. However, the groundwater systems have seen good recovery this season and will provide valuable baseflow to surface water systems and a supply of water for agriculture in the Darwin area.

The two major groundwater resources in the Darwin Rural Area, Howard East and Berry Springs, rely heavily on wet season rainfall to replenish each year. This wet season, the groundwater level at Berry Springs increased by 9 m to be within 13 m or less of the surface. The bores in Howard East and Berry Springs are not expected to increase further this year. The levels will decrease during the dry season from environmental flows and agricultural extraction.

Soil moisture

Root-zone soil moisture (in the top 100 cm) increased through April over much of southeastern Australia, compared to March. After a drier than average April in the southwest, soil moisture has decreased there.

Soil moisture for April was above average over most of New South Wales; much of Victoria except the southwest and far east; the southern third of Queensland, extending north along the Capricornia Coast, and extending across the Channel Country; across parts of the Northern Territory and the inland Kimberley; and across most of Tasmania.

Soils were drier than average for the month in Western Australia across much of the South west Land Division and areas of the interior of that State, extending north to parts of the southern Kimberley and eastern Gascoyne; for areas of inland Queensland and for scattered smaller areas of far eastern Victoria, western Victoria and southeastern South Australia which have been affected by long-term rainfall deficiencies.

Despite the first four months of 2020 being wet over large areas of eastern and western Australia, and some areas of the eastern mainland having above average rainfall for the January to April period, the influence of very low rainfall over longer timescales is still evident in the 12-month soil moisture for May 2019–April 2020, which was very much below average over very large areas of Australia.

Valuable increases in soil moisture in New South Wales

The root-zone soil moisture in April was above average to very much above average across most of the Murray–Darling Basin.

There were valuable increases in soil moisture across central and southern areas of the Murray–Darling Basin. Notably some of the Riverina agricultural area, in southwest NSW increases of more 15% of available water content in April. The Murrumbidgee and Lachlan River catchments received significant rain this month increasing soil moisture in areas that have been dry since the start of 2017.

Importantly, there were also increases in soil moisture in the major water yielding catchments of the northern and, particularly, the southern Basin. The catchments of Hume, Dartmouth, and Eildon dams, the biggest water storages in the Murray-Darling Basin, had significant increases in soil moisture this month. This is a very positive foundation going into late autumn and the beginning of the southern water storage filling season. The wetter soils mean that any rain that does now fall is more likely to result in runoff into rivers and storages.

Soil moisture decreased through the far north of the Basin, but it remains above average following major increases in February and March.

• April rainfall above average across much of the southeast
• However, April rainfall below average for much of eastern Queensland, an area extending from the western Kimberley and southern and western parts of Western Australia
• At the shorter timescale—over the nine months since August 2019—rainfall deficiencies have decreased across most affected areas in the southern half of Australia
• Rainfall deficiencies have also decreased at longer timescales—such as the 25 months since April 2018—although the accumulated rainfall deficit is significant, and deficiencies over the longer period persist in many parts of Australia
• Soil moisture has increased across much of eastern and southwest Australia, and remains above average for large areas
• Water storage levels in the northern Murray–Darling Basin remain low despite some recent inflows
• Water in the Lower Darling River reaches the Murray River