Although rainfall conditions were above average, these conditions represent a decrease in rainfall compared to the 2010–11 year (see 2011 Account), when rainfall was very much above average.The persistence of above average rainfall conditions across Melbourne contributed to inflow volumes and an approximate increase of 3% in surface water storages during the 2011–12 year (see line item 1.1 Storages).
Figure C1 Map of annual rainfall deciles for the Melbourne region during the 2011–12 year
Annual rainfall ranged from more than 1600 mm in the northeast of the region to less than 600 mm in the southwest near Melton (Figure C2).
Figure C2 Map of total annual rainfall for the Melbourne region during the 2011–12 year
The wet year observed in the Melbourne region is consistent with the above average rainfall 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 area-averaged monthly rainfall was generally close to the long-term average for most months of the reporting period. August 2011 was a particularly dry month in the Melbourne region, with area-averaged rainfall below the 10th percentile. The region experienced very high rainfall in November 2011, ranking as the sixth wettest on record and almost doubling the rainfall usually received for the month.
The reporting period concluded with above average rainfall recorded across the Melbourne region in both May and June 2012.
Figure C3 Graph of total monthly rainfall for the Melbourne region during the 2011–12 year compared with the long-term average and percentiles for the region
Evapotranspiration across the Melbourne region was generally above average for the 2011–12 year (Figure C4).
Figure C4 Map of annual evapotranspiration deciles for the Melbourne region during the 2011–12 year
The total area-averaged evapotranspiration over the Melbourne region during the 2011–12 year was 788 mm. Evapotranspiration was highest in the east of the region around Emerald and Pakenham and lowest in the west around Melton and Bacchus Marsh (Figure C5).
Figure C5 Map of total annual evapotranspiration for the Melbourne region during the 2011–12 year
The entire Melbourne region experienced mean temperatures above the long-term average during the 2011–12 year (Figure C6).
Figure C6 Map of annual meant temperature deciles for the Melbourne region during the 2011–12 year
Mean temperatures across the region ranged from more than 12 °C in the southern coastal parts of the region to less than 10 °C in the northeast of the region (Figure C7).
Figure C7 Map of annual mean temperature for the Melbourne region during the 2011–12 year
Mean temperatures in the Melbourne region were equal to or above the long-term average for all months during the reporting period, with the exception of March 2012. Mean temperatures in both August and November 2011 were above the 90th percentile, with August 2011 ranking as the third warmest August on record for the region (Figure C8).
Figure C8 Graph of average monthly mean temperature for the Melbourne region during the 2011–12 year compared with the long-term average and percentiles for the region