Annual rainfall across the Sydney region was generally average to above average for the 2010–11 year (Figure C1). The western half of the region received above average rainfall, along with the coastal region near Nowra and Kiama. The total area-averaged rainfall over the Sydney region during the 2010–11 year was 992 mm, which is above the mean annual rainfall of 890 mm. The higher rainfall provided a great deal of inflow to the storages of the Sydney region, increasing the total storage volume over the reporting period by 526,989 ML after releases and diversions.
Figure C1. Map of annual rainfall deciles for the Sydney region during the 2010–11 year
Rainfall across the region ranged from more than 1,600 mm around Kiama to less than 700 mm in areas to the north of Camden and a large area to the south of Goulburn (Figure C2).
Figure C2. Total annual rainfall for the Sydney region during the 2010–11 year
The main driver of rainfall across eastern Australia between September 2010 and March 2011 was a very strong La Niña event in the Pacific Ocean. As a result, wet conditions were experienced across much of New South Wales, including the Sydney region (although the Sydney region was less affected than most other areas of the state). The spring-time rainfall (September to November) was driven by warm ocean temperatures around the Australian continent, which brought above average rainfall to much of southern Australia, particularly the southeast.
The area-averaged monthly rainfall was close to the long-term average for most months of the reporting period and very close to the 90th percentile in November and December (Figure C3). A very wet 4-day period in late March 2011 delivered more than 300 mm across the coastal and inland area south of Wollongong and contributed to area-averaged rainfall well above the long-term average for the month.
The La Niña event concluded in April 2011 and close to average rainfall conditions prevailed across the Sydney region for the final months of the reporting period (April to June 2011).
Figure C3. Graph of total monthly rainfall for the Sydney region during 2010–11 year compared with the long-term average and percentiles for the region, based on data collected 1961–90
Evapotranspiration across the Sydney region was generally average to below average for the 2010–11 year (Figure C4).
Figure C4. Map of annual evapotranspiration deciles for the Sydney region during the 2010–11 year
The total area-averaged evapotranspiration over the Sydney region during the 2010–11 year was 816 mm. Evapotranspiration was highest around Kiama and Nowra and lowest to the south of the region between Goulburn and Braidwood and stretching as far north as Camden (Figure C5).
Figure C5. Map of annual evapotranspiration for the Sydney region the 2010–11 year
The Sydney region experienced mean annual maximum temperatures close to the long-term average during the 2010–11 reporting period (Figure C6).
Figure C6. Map of annual maximum daily temperature deciles for the Sydney region during the 2010–11 year
Mean maximum daily temperatures across the region ranged from more than 22 °C in metropolitan Sydney to less than 16 °C at the highest points along the western border of the region (Figure C7).
Figure C7. Map of annual mean maximum daily temperature for the Sydney region during the 2010–11 year
Except for January and February, monthly mean daytime temperatures for the Sydney region were near or below the long-term average throughout the year (Figure C8), although no individual month ranked below the 10th percentile. A prolonged heatwave in late January and early February resulted in Sydney's longest recorded run of consecutive days over 30 °C.
Figure C8. Graph of average monthly maximum daily temperatures for the Sydney region during 2010–11 compared with the long-term average and percentiles for the region