Canberra: Climate and water overview
Climate conditions
Rainfall
The total area-averaged rainfall over the Canberra region during the 2014–15 year was 824 mm, which is above the long-term area-averaged rainfall of 795 mm (period 1900–2015). Annual rainfall was more than 900 mm near the eastern and western region boundaries, and between 600-900 mm elsewhere. Rainfall peaked at more than 1,200 mm in a small pocket in the southeast (Figure C14).
Figure C14 Total annual rainfall for the Canberra region during the 2014–15 year
Rainfall was average to above average across most of the Canberra region for the 2014–15 year (Figure C15). These conditions represent a marginal increase in rainfall compared to the 2013–14 year (see the 2014 Account), when rainfall was average over the region. This contributed to an increase in the volume of water held in storages during the 2014–15 year.
Figure C15 Annual and monthly rainfall deciles for the Canberra region during the 2014–15 year
Climate across Australia was largely influenced by persistent near El Niño conditions in the Pacific Ocean from late-2014, and the Bureau of Meteorology declared an El Niño event in May 2015.
Below average rainfall conditions were experienced across much of Australia's southeastern region during 2014–15 year. In contrast, the Canberra region experienced average or above average monthly rainfall for six months of the 2014–15 year. Rainfall exceeded the 90th percentile for the months of December, January, and April but was only around the 10th percentile mark in July and March. The high rainfall months contributed to well above average streamflows in the Queanbeyan River. The area-averaged monthly rainfall pattern does not follow the rainfall that occurred in the upper reaches of the Cotter and Molonglo rivers where streamflow was below average (see Streamflow).
Figure C16 Total monthly rainfall for the Canberra region during the 2014–15 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 2014–15 year was 1,402 mm, which is similar to the long-term area-averaged potential evapotranspiration of 1,394 mm (based on the 1911–2015 period). Potential evapotranspiration was higher in the north and lower in south of the region (Figure C17).
Figure C17 Total annual potential evapotranspiration for the Canberra region during the 2014–15 year
Figure C18 shows that potential evapotranspiration was average across the Canberra region during the 2014–15 year.
Figure C18 Annual potential evapotranspiration deciles for the Canberra region during the 2014–15 year
Soil moisture
Figure C19 shows that soil moisture, in the root zone (0 to 1m depth) for the 2014–15 year was average to above average in the Canberra region (compared with the 1911–2015 period).
Figure C19 Annual and monthly soil moisture deciles in the root zone (0 to 1m depth) for the Canberra region during the 2014–15 year
Figure C19 also shows monthly soil moisture deciles in the root zone (0 to 1m depth) during the 2014–15 year. Comparison of monthly rainfall and soil moisture deciles show the response of soil moisture to changes in rainfall and align closely for the majority of months in the 2014–15 year.
The above average rainfall and soil moisture conditions in southeast part of the region during the 2014–15 year have contributed to above average streamflow in the Queanbeyan River (See Streamflow). Despite generally average rainfall and soil moisture conditions across the remaining part of the region, streamflow in the Molonglo and Cotter rivers was below average.
More information on soil moisture distribution across the Canberra region is available in the Australian Landscape Water Balance.
Streamflow responses
Significant water events
There were no significant water events or floods in the region during 2014–15. Above average flows in the Queanbeyan River contributed to the spilling at Googong Dam.
Streamflow
There are five major rivers within the Canberra region:
- Cotter
- Gudgenby
- Molonglo
- Murrumbidgee
- Queanbeyan.
The Murrumbidgee is the largest river system that flows through the Canberra region, with all rivers and creeks in the region draining into the Murrumbidgee River. These rivers, and the associated key gauging stations of Molonglo River at Burbong (410705), Cotter River at Gingera (410730), and Queanbeyan River upstream of Googong Dam (410781), are shown in Figure C7 in the 'Contextual information'. The river flow at gauging stations located upstream of the reservoirs is dependent on runoff from local rainfall experienced in the respective catchment.
The total annual flows in the Cotter and Molonglo rivers were approximately 45–55% of the mean annual flow for these rivers. Figures C20 and C21 show that flows in the Molonglo and Cotter rivers were below average for almost the entire year. The reduced streamflow in these rivers was primarily attributed to lower rainfall and prevailed soil moisture conditions over the catchment area upstream of the relevant gauging stations (see Figure C15 Monthly rainfall decile maps and Figure C19 Monthly soil moisture decile maps).
Conversely, total annual flow in the Queanbeyan River was approximately 150% of the mean annual flow. Flow in the Queanbeyan River was above average throughout most of the year, and close to or above the 90th percentile for mean monthly flows for six months of the year (see Figure C22). This is primarily attributed to higher rainfall over the catchment area upstream of the relevant gauging station. In addition, the upper reaches of the Queanbeyan River received more rainfall than the Molonglo River catchment.
Figure C20 Total monthly flow along the Molonglo River during 2014–15 compared with the long-term average and percentiles for the river
There are three key water storages located on the Cotter River: the Corin, Bendora, and Cotter reservoirs that supply urban water for the Canberra region. Figure C21 shows the streamflow recorded in the Cotter River upstream of Corin Reservoir. These flows enter Corin Reservoir where the water is released or spilled and flows downstream to Bendora Reservoir and eventually to Cotter Reservoir.
Figure C21 Total monthly flow along the Cotter River during 2014–15 compared with the long-term average and percentiles for the river
Googong Reservoir, southeast of Queanbeyan, is located on the Queanbeyan River, a tributary of the Murrumbidgee River. The total annual flow in Queanbeyan River was well above the long-term average annual flow. High inflows into the Googong catchment saw increased streamflows and runoff into the storage in the 2014–15 year.
Figure C22 Total monthly flow along the Queanbeyan River during 2014–15 compared with the long-term average and percentiles for the river
Major water reforms
- There were no significant enhancements to water supply or waste capacity during 2014–15.
- Icon Water sold all of its General Security entitlements held in the regulated Murrumbidgee River (12,523 ML). Icon Water still holds 9,549 ML of High Security entitlements.