Rainfall across the entire Melbourne region was very much above average during the 2010–11 year (Figure C1). A large area in the western half of the region, including parts of metropolitan Melbourne, recorded its highest annual rainfall on record. The total area-averaged rainfall over the Melbourne region during the 2010–11 year was 1,210 mm, well above the long-term average of 867 mm.
Figure C1. Map of annual rainfall deciles for the Melbourne region during the 2010–11 year
Annual rainfall totals ranged from more than 1,900 mm in mountain areas in the far northeast of the region to around 900 mm in the southwest of the region near Melton (Figure C2).
Figure C2. Map of total annual rainfall for the Melbourne region during the 2010–11 year
The above average rainfall observed in the Melbourne region is consistent with the wet year experienced across much of eastern Australia. These wet conditions were a result of a very strong La Niña event in the Pacific Ocean. La Niña conditions persisted from September 2010 through to March 2011. The spring-time rainfall (September to November) was also influenced 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 above the long-term average throughout most of the reporting period (Figure C3). The period from October to February was especially wet, with all months (except December) above the 90th percentile. Total rainfall for this 5-month period was double the long-term average. February was the wettest month of the reporting period and was three times the long-term average for the month. In early February 2011, one of the most intense rainfall events observed in the Melbourne metropolitan area delivered over 150 mm to numerous stations in just 24 hours.
Figure C3. Graph of total monthly rainfall for the Melbourne region during the 2010–11 year compared with the long-term average and percentiles for the region
The La Niña event concluded in April 2011. Close to average rainfall conditions prevailed across the Melbourne region for the final months of the 2010–11 year (March to June 2011).
Evapotranspiration across the Melbourne region was close to average for the 2010–11 year (Figure C4).
Figure C4. Map of annual evapotranspiration deciles for the Melbourne region during the 2010–11 year
The total area-averaged evapotranspiration over the Melbourne region during the 2010–11 year was 899 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 2010–11 year
The Melbourne region generally experienced mean daytime temperatures below the long-term average during the 2010-11 year (Figure C6).
Figure C6. Map of annual maximum daily temperature deciles for the Melbourne region during the 2010–11 year
Mean maximum daily temperatures across the region ranged from more than 18 °C around and to the west of the city of Melbourne to less than 14 °C at high elevations in the northeast of the region (Figure C7).
Figure C7. Map of annual mean maximum daily temperature deciles for the Melbourne region during the 2010–11 year
Monthly mean daytime temperatures for the Melbourne region were near or below the long-term average for most of the 2010–11 year (Figure C6). Whilst La Niña events have some influence on temperatures in the Melbourne region, their cooling influence is not as strong as it is further north in eastern Australia. Daily temperatures were below the 10th percentile during August and September (Figure C8), then were near normal from October to January before being generally below normal from February to May.
Figure C8. Graph of average monthly maximum daily temperatures for the Melbourne region during the 2010–11 year compared with the long-term average and percentiles for the region