National Water Account 2018

Canberra: Climate and water

  • Annual rainfall was below-average across the region for the second consecutive year.
  • Despite above-average summer rainfall, below-average rainfall throughout the rest of the year combined with poor soil moisture conditions, resulted in relatively low streamflows across the region.

 

 

For further information on the region's climate and water conditions during the 2017–18 year scroll down this page or click on the links below:

 

About the region

  • The Canberra region has a relatively dry, continental climate with warm to hot summers and cool to cold winters. Rainfall in the region is relatively uniform 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, which all contribute to the Murrumbidgee River. Higher streamflows typically occur during winter and spring, following higher runoff from partially saturated catchments in autumn and winter. Streamflows in the Murrumbidgee River can also be influenced by water diversions from the Snowy Mountain Scheme.

 

Climate conditions

Rainfall


Figure C1 Annual and monthly rainfall deciles for the Canberra region during the 2017–18 year

 

  • Total area-averaged rainfall for the year was 632 mm, below the mean value of 787 mm.
  • Above-average rainfall occurred during November–December 2017, largely due to thunderstorms bringing isolated heavy falls. Higher rainfalls occurred again in late February 2018, when a cold front brought heavy rain and flash flooding.
  • Canberra experienced its driest autumn (March–May 2018) since 2004. 

 

 


Figure C2 Total monthly rainfall for the Canberra region during the 2017–18 year compared with the average and percentiles for the region

 

  • Total rainfall was above average during the 4-month period November–February. Most other months of the year had well below-average rainfall.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration for the Canberra region during the 2017–18 year

 

  • Total area-averaged actual evapotranspiration was generally average across the region.
  • Above-average evapotranspiration during December 2017 was likely due to increased water availability following high rainfall in November–December 2017.
  • The well below-average evapotranspiration that occurred during September–October 2017 and May–June 2018 is likely due to to low water availability, following periods of very low rainfall. 

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Canberra region during the 2017–18 year

 

  • Soil moisture in the root zone (0–1 m depth) was below average to very much below average across most of the region.
  • Rainfall and soil moisture are typically closely aligned. For example, above-average soil moisture during December 2017 reflects the higher rainfall that occurred during November–December 2017. The below-average soil moisture during July–October 2017 and April–June 2018 can be attributed to the well below-average rainfall recorded for the majority of these months.
  • Above-average rainfall in February did not translate to increased soil moisture for the month because, prior to heavy rainfall in late February, Canberra was on track to have its driest February since 1986.
  • More information on soil moisture distribution across the Canberra region is available in the Australian Landscape Water Balance.

 

Flow responses

Significant water events

  • A cold front and thunderstorms brought heavy rain to the Canberra region on the 25th February, particularly the north-east of the region (see Rainfall). More than a month's worth of rain (> 60 mm) was recorded in less than 5 hours on this day at Canberra Airport, with total February rainfall 150% of the average.
  • The heavy rain on the 25th February caused severe flash flooding in the Canberra CBD, with Sullivan's Creek near Lake Burley Griffin also flooding.

 

Streamflow responses

 

Key flow gauging stations along the main rivers within the Canberra region
Figure C5 Key flow gauging stations along the main rivers within the Canberra region 

 

  • The Cotter and Queanbeyan rivers contribute most of the inflows to the storages in the Canberra region.
  • Molonglo River, one of the major tributaries of Murrumbidgee River, runs through the Canberra city centre where it is dammed to form Lake Burley Griffin.

 

 


Figure C6 Total monthly flow for major rivers in the Canberra region during the 2017–18 year compared with average and percentiles

 

  • Streamflow was very low in all three rivers for the majority of the year. 
  • In the Cotter River, streamflow spiked above average during the month of December 2017, reflecting the above-average rainfall during November-December 2017.
  • Autumn streamflow in all rivers was very much below average, reflecting the driest autumn since 2004.