Rainfall across the Melbourne region varied from average to very much below average, with below average rainfall across most of the region for the 2012–13 year (Figure C1). The total area-averaged rainfall over the Melbourne region during the 2012–13 year was 726 mm, which is below the long-term (1900–2013) area-averaged rainfall of 868 mm.
These conditions represent a decrease in rainfall compared to the 2011–12 year (see 2012 Account), when rainfall was above average. This contributed to decreased inflow volumes into the water storages during the 2012–13 year, resulting in decrease of approximately 12% in total storage volume (see line item 1.1 Storages).
Figure C1 Map of annual rainfall deciles for the Melbourne region during the 2012–13 year
Annual rainfall ranged from more than 1200 mm in small areas in the northeast of the region, to less than 500 mm in the southwest of the region including the western part of Metropolitan Melbourne (Figure C2)
Figure C2 Map of total annual rainfall for the Melbourne region during the 2012–13 year
Generally below-average rainfall was experienced across much of Australia during the 2012-13 year. There were no strong influences from large-scale climate drivers during the reporting year. Conditions in the Pacific Ocean were neutral and a negative Indian Ocean Dipole event developed developed at the end of the 2012–13 year.
The area-averaged monthly rainfall was below the long-term average for most months during the 2012–13 year, with the exception of four months (July and August 2012, February and June 2013; Figure C3). January 2013 was the fifth driest January on record for the Melbourne region, with an area-averaged value less than 15% of the long-term average. April 2013 also ranked as the seventh driest for that month.
Figure C3 Graph of total monthly rainfall for the Melbourne region during the 2012–13 year compared with the long-term average and percentiles for the region
Evapotranspiration across the Melbourne region was generally average to below average for the 2012–13 year (Figure C4). This was influenced by generally below average rainfall which limited water availability and above average temperature across the region.
Figure C4 Map of annual evapotranspiration deciles for the Melbourne region during the 2012–13 year
The total annual actual area-averaged evapotranspiration over the Melbourne region during the 2012–13 year was calculated to be 689 mm by the Australian Water Resource Assessment (AWRA version 3.0) model.
Evapotranspiration was highest in the eastern section of the region and decreased towards the central urbanised section of the region and then increased again towards the western section (Figure C5).
Figure C5 Map of total annual evapotranspiration for the Melbourne region during the 2012–13 year
The long term actual area-averaged evapotranspiration was calculated to be 697 mm using long-term data records from July 1911 to June 2012 using AWRA version 2.0 model with standard grids.
The entire Melbourne region experienced mean temperatures very much above the long-term average during the 2012–13 year (Figure C6).
Figure C6 Map of annual mean temperature deciles for the Melbourne region during the 2012–13 year
Mean temperatures across the Melbourne region ranged from more than 14 °C in northern parts of the region to less than 12 °C in isolated areas along the northwestern and northeastern borders (Figure C7).
Figure C7 Map of annual mean temperature for the Melbourne region during the 2012–13 year
Monthly mean temperatures for the Melbourne region were equal to or above the long-term average (1911–2013) for all months during the 2012–13 year (Figure C8). February and March 2013 both ranked above the 90th percentile, with the Melbourne region experiencing its eighth-warmest February and second-warmest March on record.
Figure C8 Graph of monthly mean temperature for the Melbourne region during the 2012–13 year compared with the long-term average and percentiles for the region