Drought continues or worsens after dry September
Tue 8 Oct 2019
Last month was the tenth driest September in the past 120 years of reliable rainfall records across Australia. The 2¾ years from January 2017 to September 2019 are the driest in the record book in the last 120 years in the Murray-Darling Basin as well as for NSW overall.
| September saw less than 20% of average rain across most of the country. BoM.
September again saw widespread failure of rain thanks to the most strongly positive Indian Ocean Dipole (IOD) in almost 20 years. In late September, the IOD weekly value hit an average of +1.76°, the highest since at least 2001. The IOD measures the difference in ocean temperature between the west and east tropical Indian Ocean. A strongly positive IOD shows waters to Australia's northwest are cool and produce less moisture to be carried across the continent as northwest rainbands.
September saw less than 20% of average rain across most of the country, the small exceptions being pockets of coastal SA, VIC and NSW. The TAS East Coast received a much-needed dowsing on 6-7 September. What appears to be a phenomenal rainfall streak from the Kimberley to around Alice Springs is something of an illusion - average rain there in September is minimal, so the 5 to 25mm received provided some stupendous if rather meaningless percentages. WA fared worst with the 5th driest September on record while rain in the Murray-Darling Basin was the 9th lowest. TAS did best, but was still 27% below average while VIC came second-best on 36% below.
The dry September made the nine months from January to September the 4th lowest January to September average for all Australia in the 120-year record. Added to this were above average temperatures in September which made January to September the second warmest in the 110-year record. The resulting higher than normal evaporation means that root-zone continued below average into August, the last figures available, for most of Australia.
|Rainfall deciles for the three years from 1 October 2016 to 30 September 2019. Almost all the Murray-Darling Basin lies in the bottom 10% of 3-yearly totals in the past 120 years while large areas of the basin in northern NSW and southern QLD are at record low levels. BoM.
The Monthly Drought Statement issued on Tuesday 8th shows the Murray-Darling Basin as a whole has had record low rainfall in the 2¾ years from January 2017 to September 2019 with the worst impacts being in the northern MDB. Compared to the Bureau's standard 1961 to 1990 period, MDB overall has been 37% below average, the northern MDB 40% below average and the whole state of NSW not much better at 34% below average.
The Statement says "The deficiencies have been most extreme in the northern Murray–Darling Basin, especially in the northern half of New South Wales and adjacent southern Queensland, where areas of lowest on record rainfall extend from the Great Dividing Range west as far as Dubbo and Walgett. Some of the largest rainfall deficiencies have occurred in the upper catchments of some of the major tributaries of the Darling, including the Macquarie, the Namoi–Peel, the Gwydir, and the Border Rivers."
Because of the length of the drought, most dams on the tributaries that feed the Darling River are between 1 and 8% full, and flow in the rivers at most gauges, including the Darling, is down to a trickle or has ceased. The current percentages of full capacity in the largest dams are:
- Burrendong, Macquarie River (NSW): 4.4%
- Split Rock, Manilla > Namoi Rivers (NSW): 1.6%
- Keepit, Namoi River (NSW): 0.9%
- Copeton, Gwydir River (NSW): 8.5%
- Pindari, Severn River (NSW): 4.9%
- Beardmore, Balonne River (QLD): 4.7%
- Glenlyon, Pyke Creek > Dumaresq River (QLD): 3.6%
The Menindee Lakes are effectively empty with 0% in Lakes Menindee, Pamamaroo and Cawndilla and 5% in Lake Wetherell.
This is what most of the Darling River looks like now. The sentiments are food for thought and action. And in case you're wondering, Useless Loop on Heiresson Prong does exist.
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