Basin drought: North drives record low rain­fall re­sult

The Western Star - - Rural Weekly -

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

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