Basin drought: North drives record low rainfall result
SEVERE rainfall deficiencies have driven the northern Murray Darling Basin into its worst drought on record, say Bureau of Meteorology climatologists.
BOM climate monitoring and prediction manager David Jones said rainfall records over the past 30 months showed the Northern Basin drought was below all previous records, which stretch back 120 years.
But he said while conditions in the southern Basin over the same 30 months were dry, they were not the worst on record.
“It’s really severe in the north, whereas it’s a one-in-10-year event in the south,” Mr Jones said.
“The drought (rainfall) is not the lowest on record in the southern Basin, but the average across the entire Basin is.”
While the northern Basin extremes are driving average Basin rainfall across the entire Basin to a record low, it’s the southern Basin’s rivers that are supplying the bulk of the food bowl’s irrigation water.
The Murray Darling Basin Authority’s own records show the southern catchments that drain the Great Dividing Range make the largest contributions to total run-off, despite their smaller size.
The upper Murray, Murrumbidgee and Goulburn-Broken River catchments account for about 45 per cent of the Basin’s total annual run-off from just 11 per cent of its area.
By contrast, the group of rivers flowing into the Darling River contribute 32 per cent of the Basin’s annual run-off from 60 per cent of the area.
The Darling River catchment itself accounts for 11 per cent of the Basin’s area, but less than 0.5 per cent of annual run-off.
Overall, about 86 per cent of the Basin contributes virtually no run-off to the river system, except in times of flood, including much of the northern Basin.
While southern catchments have been wet-up by recent rain, the big question for irrigators is whether follow-up falls over August to November, will deliver the rainfall run-off they need to fill dams.
At this stage the outlook does not look good, with the world’s top climate models predicting a dry late winter and spring on the back of a strong Indian Ocean dipole, which has cooled water temperatures and evaporation off the West Australian coast.
“Most models suggest positive IOD index values are likely to return and persist until the end of spring,” the Bureau of Meteorology stated in its summary of its global climate model.
Japanese climate scientists have been predicting a positive IOD since February.
It’s really severe in the north, whereas it’s a one-in-10-year event in the south.
— BOM climate monitoring and prediction manager David Jones