Cli­mate Mixed-up spring

Farms & Farm Machinery - - Contents -

In its of­fi­cial spring out­look the Bureau of Me­te­o­rol­ogy (BOM) says there are roughly equal chances of a wet­ter or drier spring (Septem­ber to Novem­ber) for most of the coun­try. Rain­fall is likely to be be­low av­er­age for south-west Aus­tralia, but parts of south-east Queens­land and far-east Gipp­s­land have a slightly in­creased chance of be­ing wet­ter than av­er­age.

On the tem­per­a­ture side, spring days and nights are ex­pected to be warmer than av­er­age for the north and south­east of the coun­try. How­ever, clear nights mean the risk of frost will con­tinue – par­tic­u­larly in ar­eas with drier soils.

Fol­low­ing an un­usu­ally dry win­ter, near-me­dian to low stream­flows are ex­pected for Au­gust to Oc­to­ber – par­tic­u­larly in the south-east of the main­land, se­nior cli­ma­tol­o­gist Robyn Duell says, adding: “Low flows are also fore­cast for the south-west and at some lo­ca­tions along the east­ern seaboard.”

More specif­i­cally, near-me­dian stream­flows are more likely at 71 lo­ca­tions across Aus­tralia, with 56 lo­ca­tions set for low stream­flows and 32 lo­ca­tions ex­pected to be high to the end of this month.

Fore­casts have not been is­sued for 22 lo­ca­tions due to very low model skill or miss­ing ob­served data.

This past win­ter was largely dom­i­nated by clear skies, par­tic­u­larly in­land across Aus­tralia, lead­ing to dry con­di­tions, cool nights and warm days, BOM cli­mate pre­dic­tion man­ager Dr An­drew Watkins says.

It was, in fact, the dri­est on record since the El Niño event of 2002-2003.

In terms of mean max­i­mum temperatures, win­ter 2017 was the warm­est on record, break­ing the old 2009 mark.

Large ar­eas of north­ern Aus­tralia ob­served record high mean max­i­mum temperatures. Queens­land, Western Aus­tralia, and the North­ern Ter­ri­tory recorded the warm­est max­i­mums on record while win­ter days were the sec­ond-warm­est on record for South Aus­tralia and third-warm­est for New South Wales.

“We’ve just ex­pe­ri­enced a very warm and dry win­ter. In fact, day­time temperatures were at record-high lev­els across much of the coun­try this win­ter,” Watkins says.

“These warm and dry con­di­tions have meant fire po­ten­tial in parts of east­ern Aus­tralia has been un­usu­ally high this win­ter.

“Bush­fires have al­ready oc­curred in north­ern NSW and south­ern Queens­land. In con­trast, win­ter nights have been cooler than av­er­age in ar­eas such as the Mur­ray–Dar­ling Basin.”

Look­ing ahead, Watkins says Aus­tralia’s main cli­mate driv­ers – the El Niño-South­ern Os­cil­la­tion (ENSO) and the In­dian Ocean Dipole – are both neu­tral at the mo­ment, so other cli­mate driv­ers are likely to in­flu­ence spring.

“Warm waters in the cen­tral In­dian Ocean may re­sult in higher pres­sures south of Aus­tralia, re­sult­ing in more east­erly winds, keep­ing the west drier than av­er­age,” he says.

In ad­di­tion, higher pres­sures to the south of the con­ti­nent will en­cour­age more east­erly flow across Aus­tralia.

In its lat­est ENSO wrap-up, the BOM says that in­ter­na­tional cli­mate mod­els sug­gest the trop­i­cal Pa­cific Ocean is likely to per­sist at ENSO-neu­tral lev­els un­til at least late 2017.

“Sea sur­face temperatures (SSTs) have cooled over much of the cen­tral trop­i­cal Pa­cific dur­ing the past sev­eral weeks, yet have re­mained within the neu­tral range,” it writes. “Other indi­ca­tors of ENSO, such as the South­ern Os­cil­la­tion In­dex

(SOI), cloudi­ness near the Date Line and trade winds are also at neu­tral lev­els.

“The In­dian Ocean Dipole (IOD) is neu­tral, though in­dex val­ues have gen­er­ally been above zero for the past sev­eral months.

“Most cli­mate mod­els sug­gest a neu­tral IOD is likely to con­tinue,” the Bureau says, adding: “How­ever, two of the six cli­mate mod­els sur­veyed sug­gest a pos­i­tive IOD may de­velop dur­ing spring.”

Pos­i­tive IOD events are typ­i­cally as­so­ci­ated with be­low-av­er­age win­ter-spring rain­fall and in­creased spring-sum­mer fire po­ten­tial over cen­tral and south­ern Aus­tralia. STREAMFLOW FORE­CASTS

The Bureau of Me­te­o­rol­ogy pro­vides seven-day streamflow fore­casts for more than 100 sites around Aus­tralia.

Com­bin­ing near real-time rain­fall and streamflow ob­ser­va­tions with rain­fall fore­casts, the BOM cal­cu­lates how much runoff is likely, and flow of this wa­ter down the stream net­work.

These 7-day streamflow fore­casts can be found at www.bom.gov.au/wa­ter/7daystream­flow

Spring will be bring­ing a wide va­ri­ety of cli­mate con­di­tions to Aus­tralia, ac­cord­ing to the Bureau of Me­te­o­rol­ogy Warm waters in the cen­tral In­dian Ocean may re­sult in higher pres­sures south of Aus­tralia, re­sult­ing in more east­erly winds, keep­ing the west drier than av­er­age

Rain­fall: To­tals that have a 75 per cent chance of oc­cur­ring for Septem­ber to Novem­ber. Source: BOM Tem­per­a­ture: The chance of above me­dian max­i­mum tem­per­a­ture for Septem­ber to Novem­ber. Source: BOM Photo: South­ern Lightscapes-Aus­tralia/Mo­ment/Getty Images

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