Annual rainfall across the Murray–Darling Basin (MDB) region was generally well above average for the 2010–11 year (Figure C1). Some areas, both in the northern and southern basins, recorded their highest annual rainfall on record based on rainfall records from 1900 to 2011. The total area-averaged rainfall over the MDB region during 2010–11 year was 779 mm, well above the mean annual rainfall of 474 mm and the third highest on record.
Figure C1. Map of annual rainfall deciles for the MDB region during the 2010–11 year
Rainfall across the region ranged from more than 2,100 mm in the southeast of the region (Alpine area) to less than 400 mm in the western part of the region close to the Queensland/New South Wales border (Figure C2).
Figure C2. Map of total annual rainfall for the MDB region during the 2010–11 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 very strong La Niña event in the Pacific Ocean. La Niña conditions persisted from September 2010 through to March 2011.
Except for January, the area-averaged monthly rainfall was above the 90th percentile from August 2010 to February 2011 (Figure C3). November 2010 ranked as the third wettest November in 111 years of record and December 2010 was the second wettest December on record. Rainfall in these two months was more than double the long-term average for these months.
The La Niña event concluded in April 2011 and below average rainfall conditions prevailed across the MDB region between April and June 2011. Rainfall in June 2011 was below the 10th percentile and less than half that usually expected for the month.
Figure C3. Graph of total monthly rainfall for the MDB region during the 2010–11 year compared against the long-term average and percentiles for the region
Figure C4 shows that evapotranspiration (ET) was above average across most of the north-western and south-western parts and below average in north-eastern part of the Murray–Darling Basin (MDB) region during 2010–11 year.
Figure C4. Map of annual evapotranspiration deciles for the MDB region during the 2010–11 year
The total area-averaged ET over the MDB region during the 2010–11 year was 710 mm. During the 2010–11 year, ET across the MDB region was highest in areas close to northern, eastern and south-eastern boundaries of the region and lowest in mid-western areas around Bourke (Figure C5).
Figure C5. Map of total annual evapotranspiration for the MDB region during the 2010–11 year
The Murray–Darling Basin (MDB) region experienced its second-coolest mean annual daytime temperatures on record (based on temperature records from 1911 to 2011) during the 2010–11 year. Mean maximum temperatures across most of the region was very much below average (Figure C6).
Figure C6. Map of annual maximum daily temperature deciles for the MDB region during the 2010–11 year
Mean maximum daily temperatures ranged from more than 28 °C in the northwest (close to the New South Wales/Queensland border) to less than 12 °C in the southeast of the region (Alpine area) (Figure C7).
Figure C7. Map of annual mean maximum daily temperature for the MDB region during the 2010–11 year
La Niña events are typically associated with cooler than average temperatures, particularly in eastern parts of Australia from October to April. Monthly mean daytime temperatures for the MDB region were below the long-term average for all months in the 2010–11 year with the exception of July, January and June (Figure C8). This is consistent with the typical effect of the La Niña on daytime temperatures.
Monthly mean daytime temperatures in November and December were below the 10th percentile due to increased cloud cover associated with the near record rainfall observed during this period. December 2010 was the second coolest December on record for the MDB region.
Figure C8. Graph of average monthly maximum daily temperature for the MDB region during the 2010–11 year compared with the long-term average and percentiles for the region