Annual rainfall across the Murray–Darling Basin (MDB) region was generally above average for the 2011–12 year (Figure C1). Several areas in the northern part of the region recorded their wettest year on record in the 2011–12 year. The total area-averaged rainfall over the MDB region during the 2011–12 year was 643 mm, which is above the long-term area-averaged rainfall of 472 mm.
Figure C1 Map of annual rainfall deciles for the MDB region during the 2011–12 year
Annual rainfall ranged from more than 2100 mm in the Victorian Alpine area in the southeast of the region to less than 300 mm in the southwest of the region close to the New South Wales/Victoria/South Australia border (Figure C2).
Figure C2 Map of total annual rainfall for the MDB region during the 2011–12 year
The above average rainfall observed in the MDB region is consistent with the wet year experienced across much of 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 – March 2012.
The area-averaged monthly rainfall was generally close to or above the long-term average for the 2011–12 year except for July 2011, and April to June 2012 (Figure C3). The region experienced high rainfall in November 2011, as well as in February and March 2012, with rainfall for all three months exceeding the 90th percentile. With more than double the usual rainfall for the month, March 2012 was the third wettest March on record for the MDB region.
The 2011–12 year concluded with generally dry conditions between April and June, with the rainfall in each of the months below the long-term average.
Figure C3 Graph of total monthly rainfall for the MDB region during the 2011–12 year compared with the long-term average and percentiles for the region
Figure C4 shows that evapotranspiration was generally above average across the western half of the region, and below average in northeastern part of the Murray–Darling Basin (MDB) region, during the 2011–12 year.
Figure C4 Map of annual evapotranspiration deciles for the MDB region during the 2011–12 year
The total area-averaged evapotranspiration over the MDB region during the 2011–12 year was 559 mm. During the 2011–12 year, evapotranspiration across the MDB region was highest in areas close to northern, eastern and southeastern boundaries of the region and lowest in southwestern areas (Figure C5).
Figure C5 Map of total annual evapotranspiration for the MDB region during the 2011–12 year
The Murray–Darling Basin (MDB) region generally experienced mean temperatures close to the long-term average during the 2011–12 year (Figure C6). In particular, northern parts of the region recorded below average temperatures while areas in the south were warmer than normal.
Figure C6 Map of annual mean temperature deciles for the MDB region during the 2011–12 year
Mean temperatures across the region ranged from more than 18 °C in the northwest (close to the New South Wales/Queensland border) of the region to less than 8 °C in the Victorian Alpine area in the southeast of the region (Figure C7).
Figure C Map of annual mean temperature for the MDB 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 MDB region were generally below average between October and April (Figure C6), with the exception of November, which is broadly consistent with the typical effect of La Niña on temperatures.
Both December 2011 and March 2012 recorded area-averaged mean temperatures below the 10th percentile. In contrast, August 2011 was much warmer than average, ranking as the fourth warmest on record.
Figure C8 Graph of average monthly mean temperature for the MDB region during the 2011–12 year compared with the long-term average and percentiles for the region