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Sta$s$calAnalysesofClimateEvents
PascalYiouLSCE
Gif-sur-Yve;e,France
ExtremeEventA;ribu$on
• Anextremeclimateeventoccurs:– Whatisitsprobability(orreturn$me)?– Hasthisprobabilitychanged(orwillit)with$me?– Howcanthischangebedescribed?– Isitrelatedtoclimatechange?
P.Yiou,WorkshopWPS,Paris2018 2
SeveralApproaches
• Largeensemblesofclimatesimula$ons(~100000)– Weather@Homeexperiments(e.g.EUCLEIAproject)
• Sta$s$calanddynamicalmodellinganddependencetoCC– Mul$-physics&Euro-CORDEXensembles
• Es$ma$ngthelinkwithlargescale– Condi$onala;ribu$ontoatmosphericcircula$on
P.Yiou,WorkshopWPS,Paris2018 3
Didanthropogenicforcingaffecttheriskofthecircula$on,heavyprecipita$onandfloodstooccurinSouthernEngland?
TheOxfordMail
www.metoffice.co.uk
P.Yiou,WorkshopWPS,Paris2018 4
Winter2013/2014
• Pressureindex:SLPat20°W,60°N
P.Yiou,WorkshopWPS,Paris2018 5
Schalleretal.,NatureClimateChange,2016
Results
Results�• Jointdistribu$on
P.Yiou,WorkshopWPS,Paris2018 6
Schalleretal.,NatureClimateChange,2016
Results�
• Increaseinriskofheavyprecipita$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
P.Yiou,WorkshopWPS,Paris2018 7
Schalleretal.,NatureClimateChange,2016
FAR =1− p0p1
OngoingResearchQues$ons
• Foragivenatmosphericpa;ern,hastheprobabilitydistribu$onoftemperature/precipita$onchanged?– Thermodynamicresponse
• Aretheretrendsintheatmosphericcircula$on?– Dynamicalresponse
P.Yiou,WorkshopWPS,Paris2018 8
AnaloguesandRecurrences
P.Yiou,SeminarLMD 9
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$onduringaperiodoutsideofthereference
10P.Yiou,WorkshopWPS,Paris2018
Circula$onanalogues(2)
• Wewanttoinferthevalueofclimatevariables(e.g.T,Prec.,Windspeed)inthedatasetT,frominforma$oninthedatabaseR.
• ForeachdayinT,findbestanaloguesofpressureinR.– Minimizedistance(Euclidean,Mahalanobis…)– Maximizespa$alcorrela$on(rank)
• Sta&s&calproper&esofanalogueT,Prec…?– “Copies”ofT,Prec.
11P.Yiou,WorkshopWPS,Paris2018
Circulation analogues (3)
• Use of daily sea-level pressure (SLP) from NCEP reanalyses
• For all days between Jan. 1st 1948 and Nov. 20th 2017, pick the 20 days within 30 calendar days but different year with the closest SLP:
– largest correlation (rank or linear) – Smallest Euclidean distance
• Determine temperature, precipitation of analogue days
12P.Yiou,WorkshopWPS,Paris2018
Day d, Year y
d,y
d±30,y’≠y
Climate observable (Temperature)
Corresponding circulation (Z500 detrended)
N best analogues
12
N
N
21
Similar to
?
Procedure
P.Yiou,WorkshopWPS,Paris2018 13(CourtesyofA.Jézéquel)
StormDirk(22Dec.2013)
14P.Yiou,WorkshopWPS,Paris2018
Uchronicprobabili$es
Probabilitydistribu$onoftemperature/precipita$onforthesamecircula$on,butwithouthumanac$vi$es.• Simula$ngmonthly(orseasonal)temperaturefromanaloguesofcircula$on– Randomsamplingofanaloguesfromtwodifferentperiods
– Es$ma$ngthedistribu$onofpossibletemperaturesforatmosphericsequencesthatareclosetotheobservedones.
P.Yiou,WorkshopWPS,Paris2018 15
Rainywinter2013/2014
P.Yiou,WorkshopWPS,Paris2018 16
Motivation Data Method Questions Results Summary
Season average precipitation fromanalogue datesNorth Atlantic domain
14 / 17
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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
• 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
P.Yiou,WorkshopWPS,Paris2018 17
Augmenta$ondelaprobabilitédeforteprécipita$ones$valeentre1930-1971et1971-2012,pourunecircula$oncyclonique
(Wilcoxetal.,Clim.Dyn.,2017)
Today’sExercise
• Circula$oninJanuary2018– StormsCarmen,Eleanor,Frederieke
• Isitexcep$onal?• UseofSLPanaloguesfromNCEP
P.Yiou,WorkshopWPS,Paris2018 18
Atoolforfastanalyses
P.Yiou,WorkshopWPS,Paris2018 19
AnalogueviewerOpensourceWPS:blackswan
Diagnos$cssta$s$quessurdesbasesdedonnéesmul$ples(CMIP,CORDEX,réanalyses)