National Water Account 2016

Murray–Darling Basin: Climate and water

Annual rainfall in the region was close to average conditions; however, most of the annual rainfall occurred in only a few months of the year, particularly January 2016 and May–June 2016. Heavy rainfall in these months resulted in high streamflows across some parts of the region. Yet rainfall and streamflow for most of the year were well below average.

 

 

Climate conditions

Rainfall

Throughout most of the 12-month period, rainfall was well below average across much of eastern Australia. Until late March 2016, Australia's climate was largely influenced by one of the stronger El Niño events since 1950. El Niño is usually associated with below-average rainfall for eastern Australia. During September–November, Australia's climate was also influenced by a positive phase of the Indian Ocean Dipole (IOD), which also contributed to the relatively dry conditions throughout southeastern Australia. Following the breakdown of the El Niño, a strong negative phase of the IOD developed contributing to the two very wet months of May and June 2016.

The total area-averaged rainfall over the Murray–Darling Basin region during the 2015–16 year was 463 mm, which is close to the long-term area-averaged rainfall of 469 mm (based on the 1900–2016 period). Annual rainfall ranged from more than 1,200 mm in the southeast to less than 200 mm in some areas across the southwestern part of the region (Figure C1).

 

Figure C1 Total annual rainfall for the Murray–Darling Basin region during the 2015–16 year
Figure C1 Total annual rainfall for the Murray–Darling Basin region during the 2015–16 year

 

Rainfall across most of the region was generally average for the 2015–16 year; rainfall was above average over the central part of the region and below average to very much below average in the southern part of the region (Figure C2).

 

Figure C2 Annual and monthly rainfall deciles for the Murray–Darling Basin region during the 2015–16 year

 

For most of the 2015–16 year, the region experienced below-average rainfall (figures C2–C3). The total annual rainfall, however, was close to average, which is largely attributed to the above-average rainfall that occurred during January 2016 and May–June 2016.

The above-average rainfall in January 2016 was primarily attributed to heavy rainfall that occurred during 4–6 January 2016 and mainly affected the southeastern part of the region (Figure C2). In May 2016, an extensive cloud band extending across the region resulted in high rainfall, particularly in central parts of the region (Figure C2). The well above-average rainfall in June 2016 was primarily attributed to two heavy rainfall events—one in early June and one in late June. Several locations, particularly in central New South Wales, recorded their wettest June on record. During the event on 4–6 June 2016, some locations in the region observed record 24-hour rainfall totals. 

 

Figure C3  Graph of total monthly rainfall for the Murray–Darling Basin region during the 2015–16 year compared with the long-term average and percentiles for the region
Figure C3 Total monthly rainfall for the Murray–Darling Basin region during the 2015–16 year compared with the long-term average and percentiles for the region

 

Evapotranspiration

The total area-averaged potential evapotranspiration over the Murray–Darling Basin region during the 2015–16 year was 1,964 mm, which was above the long-term area-averaged potential evapotranspiration of 1,922 mm (based on the 1911–2016 period). Potential evapotranspiration was higher in the northwestern part of the region and lowest along the southeastern boundary (Figure C4).

 

Figure C4 Total annual potential evapotranspiration for the Murray–Darling Basin region during the 2015–16 year
Figure C4 Total annual potential evapotranspiration for the Murray–Darling Basin region during the 2015–16 year

 

Potential evapotranspiration was above average across most of the region during the 2015–16 year (Figure C5), which may be attributed to the decreased rainfall (and hence cloud cover) that occurred over most of the year.

 

Figure C5 Annual potential evapotranspiration deciles for the Murray–Darling Basin region during the 2015–16 year
Figure C5 Annual potential evapotranspiration deciles for the Murray–Darling Basin region during the 2015–16 year

 

Soil moisture

Soil moisture in the root zone (0–1 m depth) for the 2015–16 year was average across most of the region, compared with the 1911–2016 period (Figure C6). In central areas of the region, soil moisture was above average and in the southern and northern parts of the region soil moisture was below average.

 

Figure C6 Annual and monthly soil moisture deciles in the root zone (0–1 m depth) for the Murray–Darling Basin region during the 2015–16 year

 

Rainfall and soil moisture deciles are typically closely aligned. For example, above-average soil moisture during May–June 2016 (Figure C6) reflects the above-average rainfall that occurred across the region during this period (Figure C2).

More information on soil moisture distribution across the Murray–Darling Basin region is available from the Australian Landscape Water Balance website.

 

Streamflow responses

Streamflow

The Darling River is one of the main rivers within the Murray–Darling Basin region. The location of the key gauging station at Bourke (Station 425003) along the river is provided in Figure R8 in 'Geographical information'.

Total annual flow in the Darling River during the 2015–16 year was well below average (Figure C7). Heavy rainfall during May–June 2016 (see Rainfall) did not result in above-average streamflow in the river during these months. This is likely due to high travel time for runoff to reach the gauging station and soil water stores and groundwater levels in the upstream catchment area of Darling River being relatively low following a sustained dry period.

 

Figure C7  Graph of total monthly flow for the Darling River at Bourke during the 2015–16 year compared with the long-term average and percentiles for the river
Figure C7 Total monthly flow for the Darling River at Bourke during the 2015–16 year compared with the long-term average and percentiles for the river

 

The River Murray at Doctors Point, Albury (Station 409017—see Figure R8 in 'Geographical information' for location), represents a regulated river reach downstream of major storages in the southern part of the basin. Monthly streamflows in the River Murray at Doctors Point were below average for most the 2015–16 year (Figure C8); however, the influence of rainfall on streamflow was limited due to dam operations and diversions upstream of the station.

 

Figure C8  Graph of total monthly flow for the Murray River at Doctors Point (Albury) during the 2015–16 year compared with the long-term average and percentiles for the river
Figure C8 Total monthly flow for the
River Murray at Doctors Point (Albury) during the 2015–16 year compared with the long-term average and percentiles for the river

 

The Ovens River at Peechelba (Station 403241—see Figure R8 in 'Geographical information' for location) represents a predominantly unregulated river in the basin. Total annual streamflow in the Ovens River was well below average. Monthly flows were only above average during May–June 2016 (Figure C8), reflecting the high rainfall that occurred during these months over the region (Figure C2). Total flow during January 2016 was less than expected given the above-average rainfall in the upper catchment area of Ovens River during this month (Figure C2). This is likely due to low soil moisture conditions in the catchment area following a dry winter–spring period (Figure C6).

 

Figure C9  Graph of total monthly flow for the Ovens River at Peechelba during the 2015–16 year compared with the long-term average and percentiles for the river
Figure C9 Total monthly flow for the Ovens River at Peechelba during the 2015–16 year compared with the long-term average and percentiles for the river

 

Major water reforms

New South Wales

The New South Wales Department of Primary Industries was formed on 3 July 2015. The department is responsible for water planning and policy in urban and rural areas, and ensures that the State’s interests are progressed at the national level. It also oversees government-funded water infrastructure programmes and the development of water information for the community.

On 16 June 2016, the New South Wales Government announced that it would build a new 270-km pipeline from the River Murray near Wentworth to secure Broken Hill and surrounding communities’ long-term water supply. It is estimated that the construction of the pipeline will cost $500 million, which represents New South Wales' largest investment into regional water security on record. The pipeline will address Broken Hill's concerns on insecure water supply prevailing since the city was founded in 1883.

Australian Capital Territory

The Australian Capital Territory Government’s draft plan for the management of the surface water and groundwater resources under the Murray–Darling Basin Plan was released in June 2016 for community comments (ACT Government 2016).