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Sydney: Climate and water

  • Total annual rainfall was above average for the first time in five years.
  • Heavy rainfall in March 2021 resulted in very high streamflows during that month.
  • In late March 2021 some areas experienced their worst floods in more than 30 years.

Schematic representation of the Sydney region. In 2020–21, rainfall was 1,236 mm, above average for the first time in five years. Streamflow in Shoalhaven River in 2020–21 was 747 GL compared to the average value of 231 GL. Soil moisture was above average.

For further information on the region's climate and water conditions during the 2020–21 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 2020–21 year

 

  • Total area-averaged rainfall for the year was 1,236 mm, well above the mean value of 888 mm and the region's highest in more than 30 years.
  • Rainfall during July–August 2020 was above average across most of the region, which contributed to the wettest winter since 2016.
  • Average to above-average rainfall throughout most of the spring–summer months was due to a weak La Niña that influenced Australia's climate during this period.
  • Heavy rainfall associated with a slow-moving low pressure system that impacted the region in late-March 2021 contributed to the well above-average rainfall for that month. For some areas, including the Sydney metropolitan area, the week ending 24 March 2021 was the wettest week on record (see the Bureau's 2020–21 Climate Report for more information).

 

Figure C2 Total monthly rainfall for the Sydney region during the 2020–21 year compared with the average and percentiles for the region

 

  • Rainfall in March 2021 was more than three times the monthly average and the region's second highest March rainfall on record.
  • Rainfall was also well above average in July and August 2020. In July 2020, rainfall was equivalent to the 90th percentile for that month.
  • Rainfall in April 2021 was the lowest in more than 20 years for that month.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Sydney region during the 2020–21 year

 

  • Total area-averaged actual evapotranspiration was average to above average across most of the region.
  • In November 2020, evapotranspiration was well above average across large parts of the region due to increased water availability following high rainfall in late-October and early-November 2020.
  • In the following month of December 2020, evapotranspiration was below average across almost the entire region due to very little rainfall occurring in the latter half of November and early-December 2020.
  • Evapotranspiration was above average over large parts of the region during April–May 2021 due to increased water availability following the very high rainfall in late-March 2021.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Sydney region during the 2020–21 year

 

  • Soil moisture in the root zone (0–1 m depth) was above average across almost the entire region.
  • Between August 2020–February 2021, root-zone soil moisture was generally above average over the region due to above-average rainfall throughout most of the spring–summer months.
  • Soil moisture was above average over most of the region during March–May 2021 following the very high rainfall in late-March 2021.
  • 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 2020–21 year compared with the average and percentiles

 

  • Streamflows were above average for most of 2020–21 reflecting the wet conditions experienced across the region. For example, total annual flow in the Shoalhaven River at Warri (Station 215002) was 747 GL compared to the average value of 231 GL.
  • This was the first year of high streamflow in the region's rivers since 2016.
  • Very high streamflow occurred in March 2021 due to heavy rainfall in the latter part of the month. The rainfall caused significant coastal and inland riverine flooding. Some parts of the region experienced their worst floods in more than 30 years (see the Bureau's Special Climate Statement for more information).
  • Streamflow was also high in the Shoalhaven River in August 2020 reflecting the higher rainfall during July–August over the river's catchment area in the southern part of the region (see Rainfall).