Sydney: Climate and water

  • Total annual rainfall was below average for the fourth consecutive year.
  • Heavy rainfall in February 2020 resulted in very high streamflows during that month.
  • Streamflows over the rest of the year were well below average.

Schematic representation of the Sydney region. In 2019–20, rainfall was 797 mm, less than average for the fourth consecutive year. Streamflow in Shoalhaven River in 2019–20 was 81 GL compared to the average value of 228 GL. Soil moisture was below average.

For further information on the region's climate and water conditions during the 2019–20 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 2019–20 year

 

  • Total area-averaged rainfall for the year was 797 mm, less than the mean value of 885 mm.
  • Rainfall was very low during the latter half of 2019. The below-average rainfall throughout July–December 2019 was due to a positive phase of the Indian Ocean Dipole, one of the strongest on record, that influenced Australia's climate during this period (see the Bureau's 2019–20 Climate Report for more information).
  • There was some rainfall relief during the early part of 2020 as tropical moisture associated with warmer than average sea surface temperatures off the northwest coast of Australia moved across the continent and combined with southern cold fronts to produce high rainfall across the region.
  • Heavy rainfall associated with a coastal trough that crossed the region in early February 2020 contributed to the well above-average rainfall for that month. Some areas recorded more than 400 mm (almost half the annual average) in one week during the event.

 

Figure C2 Total monthly rainfall for the Sydney region during the 2019–20 year compared with the average and percentiles for the region

 

  • Rainfall in February 2020 was the region's highest monthly total in more than 60 years.
  • Rainfall was also above average in September 2019 and March 2020. All other months had below-average rainfall.
  • Rainfall in December 2019 was the lowest on record for that month.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Sydney region during the 2019–20 year

 

  • Total area-averaged actual evapotranspiration was well below average across almost the entire region and lowest on record over inland areas of the region.
  • Evapotranspiration was below average during July 2019–January 2020 due to low water availability across the region following a dry year in 2018–19 (see the 2019 Account) combined with very low rainfall during the latter half of 2019.
  • Evapotranspiration was average over large parts of the region during February–June 2020 due to increased water availability following the high rainfall in February 2020.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Sydney region during the 2019–20 year

 

  • Soil moisture in the root zone (0–1 m depth) was below average across most of the region.
  • In July 2019, root-zone soil moisture was already below average over most of the region following a very dry 2018–19 year. Continued dry conditions during the latter half of 2019 meant that by December 2019, root-zone soil moisture was well below average and lowest on record over almost the entire region.
  • Soil moisture was above average over large parts of the region during February–April 2020 following the high rainfall in February 2020.
  • More information on soil moisture distribution across the Sydney region is available in the Australian Landscape Water Balance.

 

Streamflow responses

Map of key gauging stations. Coxs River at Island Hill, station number 212045, is in the northwestern part of the region south of Lithgow. Shoalhaven River at Warri, station number 215002, is in the southern part of the region.
Figure C5 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.
  • Streamflow along these rivers upstream of the above gauging stations is unregulated and not influenced by diversions for consumptive use.

 

Figure C6 Total monthly flow for major rivers in the Sydney region during the 2019–20 year compared with the average and percentiles

 

  • Streamflows were below average for most of 2019–20 reflecting the dry conditions experienced across the region. For example, total annual flow in the Shoalhaven River at Warri (Station 215002) was 81 GL compared to the average value of 228 GL.
  • This was the fourth consecutive year of low streamflow in the region's rivers throughout most of the year.
  • Streamflow was particularly low during the latter half of 2019. In December 2019, there was no flow in these rivers and flow in the Shoalhaven River between July–December 2019 was the lowest on record for this 6-month period.
  • Most of the annual flow in the region occurred during February–March 2020 following the above-average rainfall in February 2020. Streamflow in the Coxs River was well above the 90th percentile during February 2020 and the second highest on record for that month.