National Water Account 2018

Sydney: Climate and water

  • Total annual rainfall in the 2017–18 year was the second lowest on record since 1910.
  • Rainfall was close to average in February 2018; all other months had well below-average rainfall.
  • Poor rainfall led to very 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 Sydney region has a temperate climate with warm summers (December–February) and mild winters (June–August).
  • Rainfall occurs throughout the year with most rainfall occurring during the summer and autumn months. Higher streamflows typically occur during these months.

 

Climate conditions

Rainfall


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

 

  • Total annual rainfall was very much below average across most of the region, and lowest on record along the coastal and northern parts of the region.
  • The dominance of high pressure systems throughout most of the year resulted in a lack of low pressure systems and cold frontal activity over southern Australia, including the Sydney region. This led to drier conditions across the region compared to previous years.
  • Record low rainfall was observed at several locations across the region during July 2017, and across much of the northern and coastal part of the region during September 2017.

 

 

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

 

  • Total area-averaged rainfall for the year was 515 mm, much less than the mean value of 892 mm.
  • The total annual rainfall for the region was the second lowest in the 107 years of record.
  • Rainfall was close to average in February 2018 due to a series of weak cold fronts causing moderate falls towards the end of the month.

 

Actual evapotranspiration


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

 

  • Annual actual evapotranspiration was below average across most of the region.
  • Monthly actual evapotranspiration was mostly very much below average or below average during the year due to low rainfall.

 

Soil moisture


Figure C5 Annual and monthly soil moisture deciles for the Sydney region during the 2017–18 year

 

  • Soil moisture in the root zone (0–1 m depth) was very much below average across most the region, and lowest on record in some coastal and central parts of the region.
  • Rainfall and soil moisture are typically closely aligned. The very much below-average soil moisture for most months of the year reflects the poor rainfall conditions throughout the year.
  • More information on soil moisture distribution across the Sydney region is available in the Australian Landscape Water Balance.

 

Streamflow responses

Streamflow


Figure C6 Key flow gauging stations along the main rivers within the Sydney region
Figure C6 Key flow gauging stations along the main rivers within the Sydney region

 

  • The Hawkesbury–Nepean and Shoalhaven river systems are two primary river systems within the Sydney region.
  • Flow along these rivers upstream of the above gauging stations is unregulated and not influenced by diversions for consumptive use.

 

 

Figure C7 Total monthly flow for key rivers during the 2017–18 year compared with the average and percentiles

  

  • In both Coxs (part of the Hawkesbury–Nepean river system) and Shoalhaven rivers, streamflow was well below average throughout the entire year, which reflects the poor rainfall and soil moisture conditions across the region.
  • Annual flow in these rivers was less than 25% of the annual average.