Murray–Darling Basin
Climate overview
Rainfall
Rainfall across the Murray–Darling Basin (MDB) region was generally average to below average for the 2013–14 year (Figure C1). The total area-averaged rainfall over the MDB region during the 2013–14 year was 388 mm, which is below the long term area-averaged rainfall of 470 mm (based on the 1900–2014 period). However, MDB areas within Queensland and northern New South Wales (NSW) recorded very much below average rainfall during the 2013–14 year.
There is a very distinct difference in the rainfall pattern in the northern and Southern Basins of the MDB. Rainfall deciles are average to very much below average in Northern Basin areas and a few experienced their lowest rainfall on record. Most areas in the Southern Basin experienced generally average rainfall, with a few areas in South Australia experiencing above average rainfall, as shown in Figure C1. Western Victoria and parts of Riverina experienced drier than average conditions. These rainfall conditions are similar to the 2012–13 year (see 2013 Account), when rainfall was generally below average. The below average rainfall contributed to decreased inflow volumes into the water storages during the 2013–14 year.
Figure C1 Annual rainfall deciles for the Murray–Darling Basin region during the 2013–14 year
Annual rainfall ranged from more than 1,800 mm–1,200 mm across the southern areas of the region (along the Great Dividing Range in Victoria and New South Wales), to less than 300 mm in western parts of the region (Figure C2).
Figure C2 Total annual rainfall for the Murray–Darling Basin region during the 2013–14 year
Rainfall was well below average across much of eastern Australia during the 2013–14 year, while rainfall was well above average in parts of southern and northern central Australia. There were no strong influences from large-scale climate drivers during the year. Conditions in the Pacific Ocean were neutral, and a short-lived negative Indian Ocean Dipole event, which developed towards the end of last year, decayed at the start of the 2013–14 year. The El Niño-Southern Oscillation was also neutral for most of the year.
The area-averaged monthly rainfall was below the long term average for most months during the 2013–14 year, with the exception of February–April and June 2014 (Figure C3). Seven consecutive months (July 2013–January 2014) recorded rainfall values well below the long term area-average; October 2013 rainfall was below the 10th percentile.
Figure C3 Total monthly rainfall for the Murray–Darling Basin region during the 2013–14 year compared with the long-term average and percentiles for the region
Evapotranspiration
Figure C4 shows that potential evapotranspiration was generally above average to very much above average in the Northern Basin during the 2013–14 year. The Southern Basin had the southerly areas recording average to below average potential evapotranspiration.
Figure C4 Annual potential evapotranspiration deciles for the Murray–Darling Basin region during the 2013–14 year
The potential evaporation estimate was produced by the Australian Water Resources Assessment system landscape model (AWRA-L) version 3.0 (Van Dijk 2010). The AWRA-L model uses a modified version of the Penman–Monteith method to produce the potential evaporation. Daily AWRA-L potential evaporation grids were produced based on daily gridded climate data that were available on a 0.050 degree (approximately 5 km) national grid.
During the 2013–14 year in the Northern Basin potential evapotranspiration was highest in areas close to north western boundary and central areas decreasing towards the eastern boundary. In the Southern Basin it was higher in the western section and progressively decreased towards the southeastern section (Figure C5).
Figure C5 Total annual potential evapotranspiration for the Murray–Darling Basin region during the 2013–14 year
The total area-averaged potential evapotranspiration over the MDB region during the 2013–14 year was 1,216 mm compared to the long term area-averaged potential evapotranspiration of 1,174 mm (based on the 1970–2014 period).
Actual evapotranspiration for 2013-14 year was 369 mm, which is lower than potential evapotranspiration due to dry soil moisture conditions experienced during the year. Soil moisture deficiencies resulted from average to below average rainfall, which limited water availability, and above average temperature were recorded throughout the year. Information on soil moisture across the MDB region during the 2013–14 year is available in Soil moisture section.
Temperature
The Australian area-averaged mean temperatures were highest on record for the 12-month period ending June 2014. During the 2013–14 year, almost the entire MDB region experienced mean temperatures very much above the long term monthly averages based on the records from 1911–2014 period (Figure C6). The MDB region experienced mean temperatures which were highest on record in most of Queensland, northern and western NSW, and northern Victoria.
Figure C6 Annual mean temperature deciles for the Murray–Darling Basin region during the 2013–14 year
Mean temperatures across the MDB region ranged from more than 23°C in the northwest of the region to less than 10°C in isolated areas along the southeast border in Alpine areas of the Great Dividing Range Alpine (Figure C7).
Figure C7 Annual mean temperature for the Murray–Darling Basin region during the 2013–14 year
Monthly mean temperatures for the MDB region were above the long term average for all 12 months during the 2013–14 year (Figure C8). July and August of 2013 and January, April, and May of 2014 ranked above the 90th percentile, with the MDB region experiencing its warmest September in 2013 and fourth-warmest July 2013 and May 2014 on record.
Figure C8 Average monthly mean temperature for the Murray–Darling Basin region during the 2013–14 year compared with the long-term average and percentiles for the region