Rainfall across the entire Sydney region was above average for the 2011–12 year (Figure C1). Western and central parts of the region recorded very much above average rainfall. The total area-averaged rainfall over the Sydney region during the 2011–12 year was 1,184 mm, which is above the long-term area-averaged rainfall of 898 mm. Following from the 2010–11 year, when rainfall conditions were average to above average (see the 2011 Account rainfall), most storages in the region were at or close to capacity (see 1.1 Storages). Storage volumes increased by a total of 526,989 ML during the 2010–11 year, and by 537,432 ML in the 2011–12 year.
Figure C1 Map of annual rainfall deciles for the Sydney region during the 2011–12 year
Annual rainfall across the region ranged from more than 1,600 mm along the coast, including Sydney and Wollongong, to less than 1,000 mm in the area surrounding Goulburn (Figure C2).
Figure C2 Total annual rainfall for the Sydney region during the 2011–12 year
The above average rainfall observed in the Sydney region is consistent with the wet conditions experienced across much of northern and eastern Australia. These wet conditions were a result of a La Niña event in the Pacific Ocean and warmer than average sea surface temperatures in the Australian region. La Niña conditions persisted from October 2011 through to March 2012.
The monthly rainfall across the Sydney region was generally close to the long-term average for the reporting period. The region experienced very high rainfall in both February and March 2012, recording over 200 mm in both these months. With more than double the usual rainfall for the month, March 2012 was the fifth wettest March on record (Figure C3).
The reporting period concluded with generally close to average conditions. However, May 2012 was a dry month in the Sydney region, with an area-averaged rainfall total of just 22 mm, approximately one-third of that usually received.
Figure C3 Graph of total monthly rainfall for the Sydney region during the 2011–12 year compared with the long-term average and percentiles for the region
Evapotranspiration across the Sydney region was generally above average for the 2011–12 year (Figure C4).
Figure C4 Map of annual evapotranspiration deciles for the Sydney region during the 2011–12 year
The total area-averaged evapotranspiration over the Sydney region during the 2011–12 year was 858mm. Evapotranspiration was higher along the coastal areas of the Sydney region near Sydney, Wollongong and Kiama (Figure C5).
Figure C5 Map of annual evapotranspiration for the Sydney region during the 2011–12 year
The Sydney region experienced mean temperatures generally close to the long-term average during the 2011–12 year (Figure C6). Mean temperatures in northern parts of the region were below the long-term average.
Figure C6 Map of annual mean temperature deciles for the Sydney region during the 2011–12 year
Mean temperatures across the region ranged from more than 14 °C in the eastern parts of the region to less than 8 °C in the very south of the region (Figure C7).
Figure C7 Map of annual mean temperature for the Sydney region during the 2011–12 year
La Niña events are typically associated with cooler than average daytime temperatures in eastern parts of Australia from October to April. Monthly mean temperatures for the Sydney region were generally below average between October and April (Figure C8), with the exception of November, which is broadly consistent with the typical effect of La Niña on temperatures.
December 2011 was the coolest December on record, with an area-averaged mean temperature more than 2 °C below normal. February 2012 was also below the 10th percentile. In contrast, August and November were much warmer than average, with area-averaged mean temperatures above the 90th percentile.
The well below average temperatures recorded in February and March, in particular, are consistent with the effect of increased cloud cover as a result of above average rainfall observed across the region.
Figure C8 Graph of average monthly mean temperature for the Sydney region during the 2011–12 year compared with the long-term average and percentiles for the region