National Water Account 2016

Adelaide: Climate and water

The combination of generally below average rainfall and dry soil moisture conditions over the reporting year has seen very much below average flows in most major rivers in the region. However, higher rainfall experienced regionally in the Western Mount Lofty ranges replenished soil moisture stores and contributed to higher flows within the Onkaparinga catchment. 

 


 

 

Introduction

The Adelaide region lies within southern Australia and generally experiences mild winters and warm, dry summers. Most of the rainfall in the region falls from May–September. Rainfall can be unreliable and infrequent during summer (December–February), although some years can experience decent summer rainfall. Typically streamflow in the region's rivers reflects the distribution of rainfall throughout the year. Most storage inflows and streamflow occur during the winter months (July–August), and very little streamflow is observed during the dry summer months (December–February).

 

Climate conditions

Rainfall

Throughout the 12-month period, rainfall was very much below average across much of southeast South Australia. Until late March 2016, Australia's climate was largely influenced by one of the stronger El Niño events since 1950, as well as strong fluctuations in the Indian Ocean Dipole (IOD). The period saw record high national area-averaged temperatures, as well as reduced rainfall; with particularly dry spells during September and October. Between August and November a positive phase of the IOD became established, generally reinforcing the drying pattern observed during the El Niño and particularly across southeast Australia. Following the breakdown of the El Niño, a strong negative phase of the IOD developed, resulting in two very wet months (May and June).

The combination of these climatic conditions resulted in the total area-averaged rainfall over the Adelaide region during the 2015–16 year being 546 mm (Figure C1) , which is below the long-term area-averaged rainfall of 633 mm (based on the 1900–2016 period).

 

Figure C1  Total annual rainfall for the Adelaide region for the 2015–16 year
Figure C1 Total annual rainfall for the Adelaide region for the 2015–16 year
 

 

This was the second successive year of below average rainfall (Figure C2), where total area-averaged rainfall across the Adelaide region in 2014–15 was 445mm (see 2015 Account).

 


Figure C2 Annual and monthly rainfall deciles for the Adelaide region during the 2015–16 year  

 

During the 2015–16 year, below average rainfall was observed for the year leading into December (see Figure C2), with rainfall conditions improving through January-March, exceeding the long-term average (Figure C3). The Adelaide region experienced above average rainfall during May and June similar to that experienced throughout much of Australia.

Figure C3 Total monthly rainfall for the Adelaide region during the 2015–16 year compared with the long-term average and percentiles for the region
Figure C3 Total monthly rainfall for the Adelaide 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 Adelaide region during the 2015–16 year was 1,724 mm, which is slightly above the long-term area-averaged potential evapotranspiration of 1,659 mm (based on the 1911–2016 period). Potential evapotranspiration was highest in the north western part of the region and lowest in the south. (Figure C4).

 

Figure C4  Total annual potential evapotranspiration for the Adelaide region during the 2015–16 year
Figure C4 Total annual potential evapotranspiration for the Adelaide region during the 2015–16 year
 

 

Potential evapotranspiration was average to very much above average across most of the region and average in the southern parts of the region (Figure C5). The higher rainfall totals experienced in the east of the region meant that there was more water available for evapotranspiration than in the south or south-west.

 

Figure C5  Annual evapotranspiration deciles for the Adelaide region for the 2015–16 year
Figure C5 Annual evapotranspiration deciles for the Adelaide region for the 2015–16 year
 

 

Soil moisture

Figure C6 shows that soil moisture, in the root zone (0–1m depth) during the 2015–16 year was below average across most of the Adelaide region and average in the north (compared with the 1911–2016 period).

 


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

 

Soil moisture correlates well with rainfall experienced across the region. Soil moisture conditions remained below average for the first part of the reporting year with a lack of rain causing soil moisture levels to decrease to very much below average from October–January across most of the Adelaide region. Above average rainfall from January–March slightly improved soil moisture, but a very dry April saw conditions decline again. The breakdown in El Niño and the subsequent rainfall events in May and June meant that soil conditions improved to average levels in most of the region and above average to the north.

More information on soil moisture distribution across the Adelaide region is available in the Australian Landscape Water Balance.

 

Streamflow responses

Streamflow

Onkaparinga River mouth, SA (iStock © Sharon Wills)

There are three primary river systems within the Adelaide region:

  • Myponga
  • North Para
  • Onkaparinga.

The locations of the key gauging stations at Myponga (Station A5020502), North Para (Station A5050502) and Onkaparinga (Station A5030504) are provided in Figure R4 in 'Geographic information'.

Following well below average rainfall in 2014–15 all major rivers in the region were exhibiting below average streamflow from July–September (figures C7-C9).

Data are missing from January–June for the Myponga River (Figure C7), however streamflow patterns in the North Para show the result of continued dry conditions for the first half of 2016. The rainfall experienced from January–March contributed mainly to replenishing the diminshed soil moisture and contributed little to runoff for this catchment. The North Para River responded slightly to the rainfall in May–June but had started to decline by the end of the reporting year ended (Figure C8).

Several low pressure systems that passed through the region in early September delivered rainfall mainly in the Onkaparinga catchment (Figure C9), leading to above average flows recorded from October until June. Further rainfall in January saw river levels exceeding 90th percentile flows for both January and February. The wet conditions observed in May meant that flow in the Onkaparinga River continued to be above the long-term average for the rest of the year.

 

Figure C7 Monthly flow along the Myponga River during the 2015–16 year compared with the long-term average and percentiles for the river

Figure C7 Monthly flow along the Myponga River during the 2015–16 year compared with the long-term average and percentiles for the river

 


Figure C8  Monthly flow along the North Para River during the 2015–16 year compared with the long-term average and percentiles for the river

Figure C8 Monthly flow along the North Para River during the 2015–16 year compared with the long-term average and percentiles for the river

 

 

Figure C9  Monthly flow along the Onkaparinga River during the 2015–16 year compared with the long-term average and percentiles for the river

Figure C9 Monthly flow along the Onkaparinga River during the 2015–16 year compared with the long-term average and percentiles for the river 

 

Major water reforms

Ongoing major water reforms in the Adelaide region include the unbundling of water rights and development of the Adelaide Plains water allocation plan, described in detail below. SA Water also has several projects ongoing, that are ultimately aimed at achieving efficiencies in water treatment and reuse. Refer to the SA Water current projects website for further information.

Adelaide Plains water allocation plan

Ongoing development of a combined water allocation plan for Central Adelaide Prescribed Wells Area and Northern Adelaide Plains Prescribed Wells Area has been carried out by the Adelaide and Mount Lofty Ranges Natural Resources Manangement Board and South Australian Department of Environment, Water and Natural Resources.

Northern Adelaide Irrigation Scheme

The Northern Adelaide Irrigation Scheme (NAIS) presents an opportunity to expand the use of recycled water in the Northern Adelaide Plains. The scheme will make available up to 20,000 ML of water from the Bolivar Wastewater Treatment Plant to be used to expand horticultural irrigation in the region. Further information on the proposal is available at SA Water current projects website.

Unbundling water rights

Progressive separation of water rights pursuant to Action 61 of the Water for Good plan has been carried out, so they can be managed as four separate items (refer to the Department of Environment, Water and Natural Resources website for further information).