Stas$cal Analyses of Climate Events · • For all days between Jan. 1st 1948 and Nov. 20th 2017,...

Sta$s$calAnalysesofClimateEvents

PascalYiouLSCE

Gif-sur-Yve;e,France

ExtremeEventA;ribu$on

•  Anextremeclimateeventoccurs:– Whatisitsprobability(orreturn$me)?– Hasthisprobabilitychanged(orwillit)with$me?– Howcanthischangebedescribed?–  Isitrelatedtoclimatechange?

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SeveralApproaches

•  Largeensemblesofclimatesimula$ons(~100000)– Weather@Homeexperiments(e.g.EUCLEIAproject)

•  Sta$s$calanddynamicalmodellinganddependencetoCC– Mul$-physics&Euro-CORDEXensembles

•  Es$ma$ngthelinkwithlargescale– Condi$onala;ribu$ontoatmosphericcircula$on

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Didanthropogenicforcingaffecttheriskofthecircula$on,heavyprecipita$onandfloodstooccurinSouthernEngland?

TheOxfordMail

www.metoffice.co.uk

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Winter2013/2014

•  Pressureindex:SLPat20°W,60°N

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Schalleretal.,NatureClimateChange,2016

Results

Results�•  Jointdistribu$on

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Schalleretal.,NatureClimateChange,2016

Results�

•  Increaseinriskofheavyprecipita$on(FAR):! 40%[0%:160%]

20 50 100 200 500

3.8

4

4.2

4.4

4.6

4.8

5

5.2

5.4

Return period [years]

Janu

ary

mea

n pr

ecip

itatio

n [m

m/d

ay]

Actual Conditionspooled Naturalindividual Natural

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Schalleretal.,NatureClimateChange,2016

FAR =1− p0p1

OngoingResearchQues$ons

•  Foragivenatmosphericpa;ern,hastheprobabilitydistribu$onoftemperature/precipita$onchanged?– Thermodynamicresponse

•  Aretheretrendsintheatmosphericcircula$on?– Dynamicalresponse

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AnaloguesandRecurrences

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Twoanaloguemapscorrespondtoclosepointsinphasespace

(CourtesyofD.Faranda)

Circula$onanalogues(1)

•  ReferencedatabaseR,containingconsistentpressure(SLPand/orgeopoten$alheights),temperature,precipita$onetc.dataduringareferenceperiodofobserva$ons–  E.g.Reanalysisdataforafixedperiod,climatemodelcontrolsimula$on

•  TargetdatasetT,withonlypressuredata(SLPorgeopoten$alheight)–  E.g.Observa$onduringaperiodoutsideofthereference

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Circula$onanalogues(2)

•  Wewanttoinferthevalueofclimatevariables(e.g.T,Prec.,Windspeed)inthedatasetT,frominforma$oninthedatabaseR.

•  ForeachdayinT,findbestanaloguesofpressureinR.– Minimizedistance(Euclidean,Mahalanobis…)– Maximizespa$alcorrela$on(rank)

•  Sta&s&calproper&esofanalogueT,Prec…?– “Copies”ofT,Prec.

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Circulation analogues (3)

•  Use of daily sea-level pressure (SLP) from NCEP reanalyses

•  For all days between Jan. 1st 1948 and Nov. 20th 2017, pick the 20 days within 30 calendar days but different year with the closest SLP:

–  largest correlation (rank or linear) –  Smallest Euclidean distance

•  Determine temperature, precipitation of analogue days

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Day d, Year y

d,y

d±30,y’≠y

Climate observable (Temperature)

Corresponding circulation (Z500 detrended)

N best analogues

12

N

N

21

Similar to

?

Procedure

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StormDirk(22Dec.2013)

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Uchronicprobabili$es

Probabilitydistribu$onoftemperature/precipita$onforthesamecircula$on,butwithouthumanac$vi$es.•  Simula$ngmonthly(orseasonal)temperaturefromanaloguesofcircula$on–  Randomsamplingofanaloguesfromtwodifferentperiods

–  Es$ma$ngthedistribu$onofpossibletemperaturesforatmosphericsequencesthatareclosetotheobservedones.

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Rainywinter2013/2014

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Motivation Data Method Questions Results Summary

Season average precipitation fromanalogue datesNorth Atlantic domain

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Slovenia Southern England Northern Franceregion

win

ter a

vera

ge p

reci

pita

tion

[mm

/day

]

● 1950−20122013

climatology 1960−2012analogue 1950−1979 NAanalogue 1984−2013 NA

Analogue precipitationfrom 1950-1979 is lowerthan the 53y climatology

Analogue precipitationfrom the 1984-2013period is clearly higher inall regions but exceedsthe climatology only forSouthern England

No analogue precipitationgets close to theclimatology in Slovenia

•  Donnéesdecircula$onNCEP•  Observa$onsdetempératureUKMOetMétéo-France

! Augmenta&ondelaprécipita&onmoyenne,àcircula&onfixée

Motivation Data Method Questions Results Summary

Season average precipitation fromanalogue datesNorth Atlantic domain

14 / 17

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0

2

4

6

Slovenia Southern England Northern Franceregion

win

ter a

vera

ge p

reci

pita

tion

[mm

/day

]

● 1950−20122013

climatology 1960−2012analogue 1950−1979 NAanalogue 1984−2013 NA

Analogue precipitationfrom 1950-1979 is lowerthan the 53y climatology

Analogue precipitationfrom the 1984-2013period is clearly higher inall regions but exceedsthe climatology only forSouthern England

No analogue precipitationgets close to theclimatology in Slovenia

Rainy2012summerinUK

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SEEP SWEP CEP NWEP NEEP SSP NSP ESP NIP

0.5

1.0

2.0

rho=p1/p0

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Augmenta$ondelaprobabilitédeforteprécipita$ones$valeentre1930-1971et1971-2012,pourunecircula$oncyclonique

(Wilcoxetal.,Clim.Dyn.,2017)

Today’sExercise

•  Circula$oninJanuary2018– StormsCarmen,Eleanor,Frederieke

•  Isitexcep$onal?•  UseofSLPanaloguesfromNCEP

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Atoolforfastanalyses

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AnalogueviewerOpensourceWPS:blackswan

Diagnos$cssta$s$quessurdesbasesdedonnéesmul$ples(CMIP,CORDEX,réanalyses)