National Water Account 2016

Canberra: Climate and water

Annual rainfall in the region was above average, which is largely attributed to heavy rainfall associated with an east coast low event that occurred during 5–6 June 2016. The event resulted in very high streamflows across the region throughout June 2016. Yet rainfall and streamflow during the majority of the year were below average.

 

 

Introduction

The Canberra region has a relatively dry, continental climate with warm to hot summers and cool to cold winters. Rainfall in the region is almost equally distributed throughout the year with a long-term monthly average of 50–75 mm.

The main rivers in the region are the Molonglo, Cotter and Queanbeyan rivers, which all contribute to the Murrumbidgee River. The majority of flow typically occurs during autumn and winter when evapotranspiration is relatively low. Streamflows in the Murrumbidgee can also be influenced by water diversions from the Snowy Mountain Scheme (see Water resources in 'Region description' for more information).

 

Climate conditions

Rainfall

Throughout most of the 12 month period, rainfall was very much below average across much of southeastern Australia. For most of this period, up until late March 2016, Australia's climate was largely influenced by one of the strongest El Niño events since 1950. El Niño is usually associated with below average rainfall for southeastern Australia. Following the breakdown of the El Niño, a strong negative phase of the Indian Ocean Dipole developed, contributing to two very wet months (May and June) at the end of the year.

Total area-averaged rainfall over the Canberra region during the 2015–16 year was 847 mm, which is above the long-term area-averaged rainfall of 795 mm (based on the 1900–2016 period). Annual rainfall was more than 900 mm near the eastern and western region boundaries and between 600–900 mm elsewhere (Figure C1).

 

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

 

Rainfall across most of the region was average for the 2015–16 year; rainfall in the southeast of the region was above average (see Figure C2).

 


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

 

The above-average rainfall across the Canberra region during the 2015–16 year is largely attributed to an east coast low event that occurred over 5–6 June 2016. This event also contributed to the second highest monthly rainfall total for June on record (Figure C3). The higher rainfall totals during this event occurred in the southeastern part of the region. At some locations in the area, more than 250 mm of rainfall was observed in the 48-hour period, equivalent to a greater than 1-in-50-year rainfall event.

Prior to the east coast low event, rainfall for the majority of the 2015–16 year was below average. Including June 2016, only four months recorded above average monthly rainfall (Figure C3).

 

Figure C3 Total monthly rainfall for the Canberra region during the 2015–16 year compared with the long-term average and percentiles for the region

 
Figure C3 Total monthly rainfall for the Canberra 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 Canberra region during the 2015–16 year was 1,458 mm, which is above the long-term area-averaged potential evapotranspiration of 1,413 mm (based on the 1911–2016 period). Potential evapotranspiration was relatively uniform across the region but marginally higher in the southern parts (Figure C4).

 

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

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

 

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

 

Figure C5 Annual potential evapotranspiration deciles for the Canberra region during the 2015–16 year

 Figure C5 Annual potential evapotranspiration deciles for the Canberra 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 Canberra region, compared with the 1911–2016 period (Figure C6).

 

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

 

Similar to rainfall, soil moisture was below average for the majority of the year (Figure C6). Soil moisture was only above average across most the region for two months of the year—February 2016 and June 2016—which can be attributed to the high rainfall that occurred during January 2016 and June 2016, respectively (Figure C3).

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

 

Streamflow responses

Streamflow

The Cotter and Queanbeyan rivers contribute most of the inflows to the storages in the Canberra region. The locations of key gauging stations of Molonglo River at Burbong (410705), Cotter River at Gingera (410730), and Queanbeyan River upstream of Googong Reservoir (410781) are shown in Figure R7 in the 'Geographic information'.

In both the Molonglo and Cotter rivers, monthly flows were well below average for most of the 2015–16 year (figures C7–C8). The exception was June 2016, where monthly flows were well above average. These very high flows were primarily attributed to an east coast low event that occurred 5–6 June 2016 (see Climate conditions).

Above average rainfall experienced in November 2015 and January 2016 did not result in above average streamflows in these rivers during these periods as soil moisture conditions were relatively low in the upper catchment areas following a dry spring and early-summer period (Figure C6).

 

Figure C7 Total monthly flow along the Molonglo River during 2015–16 compared with the long-term average and percentiles for the river

Figure C7 Total monthly flow along the Molonglo River during 2015–16 compared with the long-term average and percentiles for the river

 

 Figure C8 Total monthly flow along the Cotter River during 2015–16 compared with the long-term average and percentiles for the river

Figure C8 Total monthly flow along the Cotter River during 2015–16 compared with the long-term average and percentiles for the river

 

In the Queanbeyan River, monthly flows were also below average for most of the 2015–16 year and generally reflected the rainfall conditions experienced in the region (Figure C9). Similar to the Molonglo and Cotter rivers, monthly flow in June 2016 was well above average due to the east coast low event that occurred 5–6 June 2016. The higher rainfall totals during this event occurred in the upper catchment area of the Queanbeyan River (see Climate conditions). Consequently, flows in this river were relatively much higher than flows experienced in the Molonglo and Cotter rivers.

 

Figure C9 Total monthly flow along the Queanbeyan River during 2015–16 compared with the long-term average and percentiles for the river
Figure C9 Total monthly flow along the Queanbeyan River during 2015–16 compared with the long-term average and percentiles for the river

 

Major water reforms

Organisational change

In May 2016 the Queanbeyan City Council and Palerang Council were merged to form the Queanbeyan–Palerang Regional Council. For the 2016 Account, the Queanbeyan–Palerang Regional Council reported the volumes applicable to the former Queanbeyan City Council area, similar to previous years reported by the Queanbeyan City Council.

Infrastructure development

In February 2016 the Queanbeyan City Council commenced operations of a newly-built sewerage water treatment and recycling plant at Googong township.