Rainfall across the Ord region was generally above average for the 2011–12 year (Figure C1). Western and southern parts of the region recorded above or very much above average rainfall. The total area-averaged rainfall over the Ord region during the 2011–12 year was 771 mm, which is above the long-term area-averaged rainfall of 673 mm.
Figure C1 Map of annual rainfall deciles for the Ord region during the 2011–12 year
Rainfall across the region ranged from more than 1,000 mm along the northern coastal region to less than 600 mm in the south near Halls Creek (Figure C2).
Figure C2 Map of total annual rainfall for the Ord region during the 2011–12 year
The above average rainfall observed in the Ord 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 the reporting period. The region experienced very high rainfall in the early part of the wet season (October–November) and again in the final months of the wet season (March–April), with three months receiving rainfall above the 90th percentile (Figure C3). November 2011 was the sixth wettest November on record, with an area-averaged rainfall total approximately double that usually received for the month.
Figure C3 Graph of total monthly rainfall for the Ord region during the 2011–12 year compared with the long-term average and percentiles for the region
Evapotranspiration across the Ord region was generally above average for the 2011–12 year (Figure C4). The above average evapotranspiration reflects the above average rainfall experienced across the entire region, particularly during the early part of the wet season (October–November) (see Rainfall). As a result of this early rainfall, it is likely more water would have been available for evaporation, particularly during the hotter parts of the year (December–February).
Figure C4 Map of annual evapotranspiration deciles for the Ord region during the 2011–12 year
The total area-averaged evapotranspiration over the Ord region during the 2011–12 year was 717 mm. Evapotranspiration was highest in the north along the coast and lowest along the southern part of the region around Halls Creek (Figure C5).
Figure C5 Map of total annual evapotranspiration for the Ord region during the 2011–12 year
The Ord region experienced mean temperatures cooler than the long-term average during the 2011–12 year (Figure C6). Mean temperatures in the western and southern parts of the region were very much below the long-term average.
Figure C6 Map of annual mean temperature deciles for the Ord region during the 2011–12 year
Mean temperatures across the region ranged from more than 26 °C in the area surrounding Wyndham to less than 24 °C in the southern parts of the region (Figure C7).
Figure C7 Map of annual mean temperature for the Ord region during the 2011–12 year
La Niña events are typically associated with cooler than average temperatures in northern parts of Australia from October–April. Monthly mean temperatures for the Ord region were generally below average between October and April (Figure C8), with the exception of January and February, which were close to the long-term mean. This is broadly consistent with the typical effect of La Niña on temperatures. November 2011 was the fifth coolest November on record for the region.
The well below average temperatures recorded during the reporting period are consistent with the effect of increased cloud cover as a result of above average rainfall observed across the region. This was particularly evident in November 2011 when high rainfall totals led to very low mean temperatures.
Figure C8 Graph of average monthly maximum daily temperature for the Ord region during the 2011–12 year compared with the long-term average and percentiles for the region