Australia’s climate in 2015: cool to start with a hot finish

(The Conversation)

TodaytheAustralianBureauofMeteorologyhasreleaseditsyearlyclimateupdate.AstrongElNiñoeventwastheheadlinestoryunderlyingglobalclimatein2015,butitsimpactinAustraliawasmixed.

Insomepartsofthecountryitwasaverydryyear,butsomeotherpartswhicharenormallyhithardbyElNiño–especiallylargepartsofNewSouthWales–gotoffratherlightly.RecordhightemperaturesintheIndianOceanwerepartofthemix,providingasourceofmoistureattimesoverautumnandwinterwhichoffsetthedryinginfluenceofElNiño.

Afterafalsestartinlate2014,full-blownElNiñoconditionsdevelopedinthetropicalPacificOceanbyMay2015.TheeventintensifiedrapidlyandwentontobecomeoneofthestrongestElNiñoeventsofthelast50years,alongside1982-83and1997-98.

Inmanypartsoftheworld,ElNiño’simpactonclimatefollowedtheusualscript.Inparticular,therewasseriousdroughtinthesecondhalfoftheyearinIndonesia,PapuaNewGuineaandmanyofthewesternSouthPacificislands,alongwithnorthernSouthAmerica,CentralAmericaandtheCaribbean.InAustralia,thesituationwasmorecomplicated.

VerydryinpartsofAustralia

Nationally,rainfallin2015wasbelownormal,althoughnowherenearrecord-breakinglevels.Thenationalannualtotalwas5%belowthe1961-1990average.

Asubstantialproportionof2015’srainfellinJanuary,especiallyinnorthernandcentralAustralia.AliceSpringshadthree-quartersofitsannualaveragerainfallinthespaceofaweek(andthenhadonly10millimetresinthenextninemonths).IfJanuarywastakenoutofthepicturetheyearwasmuchdrier.TheFebruary-Novemberperiodwastheninth-driestonrecordnationally,andinthenorthernhalfofAustraliaitwasthedriestsince1951.HeavyrainreturnedinDecemberinthenortherntropics,particularlytheNorthernTerritory,whichhaditswettestDecemberonrecord.

Thestandoutdryregionsof2015werethesouthwestofWesternAustraliaandaregionofthesoutheastencompassingcentralandwesternVictoria,thesoutheastofSouthAustralia,andpartsofTasmania.

InthesouthwestofWesternAustraliaaveragerainfallfortheMay-Novembergrowingseasonwasthesecondlowestonrecordafter2010.Tasmaniarankedseventh-driestforthisperiod,andVictoriaeleventh.

SpringwasespeciallydryinTasmania,whereitwaseasilythedriestonrecord,andbothTasmaniaandVictoriahadtheirdriestyearssince2006.

InbothsouthwestWesternAustraliaandVictoria,thedryconditionsin2015wereanintensificationonlong-termrainfalldeficitslastingseveralyears,withVictorianrainfallsincemid-2012returningtolevelstypicalofthe1997to2009MillenniumDrought.

2015wasalsoarelativelydryyearformuchofinlandQueenslandandadjacentnorthernNewSouthWales.

Someofthehardest-hitdroughtareasdidabitbetterthantheyhadin2013or2014andnorthwestQueenslandhadusefulrainattheendof2015.Butrainfallwasstillgenerallybelownormalandnotenoughtomakeanyseriousinroadsintothemulti-yeardroughtafflictingtheregion.

ItwasalsoanotablydryyearinpartsofcoastalnorthQueensland,withTownsvilleamongthecentreshavingitsdriestyearonrecord.SomecoastalregionsfurthersouthhadheavyraininFebruaryfromCycloneMarcia,whichmadelandfallnorthofRockhampton,thesouthernmostknowncategory5cyclonelandfallontheQueenslandcoast.

Incontrasttothedrynessfurthernorthandsouth,NewSouthWaleshadnear-normalrainfallin2015.Theinlandreceivedreasonablyregularrainthroughtheyear,whilethecoasthadseveralmajordownpoursassociatedwitheastcoastlows.DestructivefloodingaffectedtheHunterregioninAprilandtheIllawarrainAugust.

TherainfallextendedtosoutheastQueensland.Brisbanehaditssecond-wettestyearofthe21stcentury,withparticularlyheavyraininearlyMayandnumerousseverethunderstormsduringthespring.

Coolstart,hotend

ForAustralianmeantemperaturesitwasayearoftwohalves.Autumntemperatureswereslightlybelownormal,butitwasanexceptionallywarmfinishtotheyear.Thelastquarter(October-December)oftheyearwaseasilythehottestonrecord.Overtheyearasawhole,temperatureswere0.83°Cabovethe1961-90average,makingitthefifthwarmestyearonrecord.

2013,2014and2015haveallrankedinthefivewarmestyearsonrecordforAustralia.ThelastthreeyearshavealsoseenAustralia’sthreewarmestsprings,with2015fallingjustshortof2014’srecordhigh.Australia’s2015temperatureswererelativelymodestbyglobalstandards,withtheworldsettohaveitshottestyearonrecordbymorethan0.1°Cabovetherprevioushottestyear(2014).Finalglobalnumbersfor2015willnotbeavailableuntillaterthismonth.

ThewarmthinAustraliawasespeciallyexceptionalinOctober.Nationally,temperatureswere2.89°Cabovethe1961-90average,whichintermsofdegreesaboveaveragemakesitthemostextrememontheverexperiencedforAustraliantemperatures.

MostofthesouthernhalfofmainlandAustraliahaditshottestOctoberonrecord,withaveragemaximumtemperaturesforthemonthmorethan7°CabovenormalinpartsofVictoria.Victoria’sOctobertemperatureswereaboutthoseofanormalDecember.

Melbournehaditsearliest-everspringdayabove35°C,andSydneyitssecond-earliest.Theheatduringspringwasassociatedwithanumberofmajorunseasonablefiresacrossthesouthernstateswithlossoflifeandproperty.TherewasfurtherextremeheatinDecember,withMildurarecordingVictoria’shighest-everovernightminimumtemperature(31.9°C),andVictoria,TasmaniaandSouthAustraliaallexperiencingtheirhottestDecembersonrecord.

2015’swarmthextendedovermostpartsofthecountry,withtemperaturesabovenormaleverywhereexceptpartsoftheinteriornorthwestandsouthernTasmania.ThewarmthwasmostpronouncedinWesternAustraliaandQueensland.Temperatureswere1.0to1.5°CaboveaverageovermostofWesternAustraliaoutsideoftheKimberley,aswellasovermostofsouthernandcentralQueensland,apartfromtheeastcoastfromMackaysouthwards.

ItwasthehottestyearonrecordinpartsofsouthernWesternAustraliaandwasthesecondhottestyearfortheStateasawhole,whilstrecordswerealsosetinQueenslandinaregioncentredonTownsvilleandinpartsofthecentralandsoutherninterior.

Oneexceptiontothewarmthcameinwinter,whenitwasrathercoldoverthesoutheastquarterofthecountry.Tasmaniahaditscoldestwintersince1966andVictoriaitscoldestsince1997,althoughVictoriantemperatureswerestillonly0.26°Cbelowaverage.Thecoldextendedfurthernorthinmid-July,bringingthemostsignificantsnowfallssince1984tohigherelevationsinQueenslandandnorthernNewSouthWales.

WinterinNewSouthWaleswas0.22°Caboveaverage.Thestatehasnowhadeighteenwintersinarowwithabove-normaltemperatures,anindicationofhowrarecoldwintershavebecomeinrecentyears.

ElNiñoisexpectedtodeclineoverthefirsthalfof2016,althoughitremainstobeseenwhetheritwilltransitiondirectlyintoaLaNiñaevent(ashappenedin1998)orreturntonear-normal(neutral)conditions.

Historically,adecliningElNiñotypicallyhaslimitedinfluenceonAustralianrainfallfromJanuaryonwards,butisstillassociatedwithhighertemperatures,especiallyinthefirsthalfoftheyear.