Analysis of extremes in a changing climate in support of informed decisions for adaptation

EURANDOM & KNMI, May 2009

Analysis of extremes in a changing climate in support of informed

decisions for [email protected]


Agenda• Changing climate extremes

• Traditional practices

• WMO guidance document

• Analyses of extremes

• Take home message



Changing climate extremes• IPCC-AR4: ‘confidence has

increased that some extremeswill become more frequent,more widespread and/or moreintense during the 21st century’



Changing climate extremes• Definitions?

– High impact events– Exceedence of a relatively low threshold (e.g., 95th

percentile of daily precipitation amounts)– Rare events (long return periods)– Unprecedented events (in the available record)


Changing climate extremes• Definitions?

– High impact events– Exceedence of a relatively low threshold (e.g., 95th

percentile of daily precipitation amounts)– Rare events (long return periods)– Unprecedented events (in the available record)

• Wide range of space and time scales– From very small scale (tornadoes) to large scale (drought)


Extremes table IPCC-AR4, WG1 report


Traditional practices• Design criteria for safety

of infrastructure aretypically based onhistorical observationsof extremes, assuminga stationary climate


Traditional practices• Design criteria for safety

of infrastructure aretypically based onhistorical observationsof extremes, assuminga stationary climate

• Methods fit extreme valuedistributions to selectedobservations of extremes


Annual maxima of daily precipitation amountsStation De Bilt, the Netherlands, 1906-2003


EVT estimates: 70 mm: once in 50yr 50 mm : once in 5yr

Map of daily rainfall, 31 July 2002


31 July 200211 August 2002


31 July 200211 August 200224 August 2002


• Climate change makes it likely that there will be change in some extremes that lies outside the envelope of constant variability assumed under stationary climate conditions

Traditional practices


• Climate change makes it likely that there will be change in some extremes that lies outside the envelope of constant variability assumed under stationary climate conditions

• Adaptation strategies should begin to take into account the observed and projected changes in extremes

Traditional practices


• A new WMO/WCRP guidance document on this topic is now in press:

– Albert M.G. Klein Tank, Francis W. Zwiers and Xuebin Zhang, 2009: Analysis of climate and weather extremes in a changing climate in support of informed decisions for adaptation. WMO/TD-No ????

WMO Guidance document


• Targeted at National Meteorological and Hydrological Services (NMHSs) around the world

• Aim is:– to help build capacity to identify and describe changes in

extremes, and– to improve the information services on extremes under

climate change conditions



• The focus is on climate extremes defined as rare events within the statistical reference distribution of particular weather elements that are monitored daily at a particular place, such as temperature and precipitation

• More complicated weather elements that involve compound factors, such as tropical cyclones or storm surges, fall outside the scope



• Need long and quality controlled observational series with high time resolution

Analysis of extremes

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TN, Amos (Canada)


• Tests for nonclimatic jumps and/or gradual shifts due to changes in station location, environment (exposure), instrumentation or observing practices



• For analyzing moderate extremes an internationally coordinated set of descriptive indices can be used, which describe frequency, amplitude, persistence

• User-friendly R-based software (RClimDex) for their calculation is available from http://cccma.seos.uvic.ca/ETCCDI


http://cccma.seos.uvic.ca/ETCCDI




• For analyzing moderate extremes an internationally coordinated set of descriptive indices can be used, which describe frequency, amplitude, persistence

• User-friendly R-based software (RClimDex) for their calculation is available from http://cccma.seos.uvic.ca/ETCCDI

• One key approach involves counting the number of days in a season or a year that exceed specific thresholds






upper 10-ptile 1961-1990

the year 1996

lower 10-ptile1961-1990




the year 1996


“cold nights”




the year 1996


“warm nights”

“cold nights”



De Bilt, the Netherlands



AR4 map of observed trends(days per decade) for 1951 to 2003

(Alexander et al., JGR, 2006)

Analysis of extremes• The results (in a

series of journalpapers) contributedto IPCC-AR4, Ch3


• The results (in aseries of journalpapers) contributedto IPCC-AR4, Ch3

– Workshops heldpost-AR4

– New workshopsorganized in 2009 AR4 map of observed trends

(days per decade) for 1951 to 2003 (Alexander et al., JGR, 2006)




Linking the trends in extremes indices to regional circulation changes

Example for Europe (van den Besselaaret al., Theor. Appl. Climatol, in press)


• Classic EVT provides a framework for analyzing extremes further in the tails of the statistical distributions




• Possible to account for “non-stationarity”, but the best way to do this is still under debate




• Possible to account for “non-stationarity”, but the best way to do this is still under debate

• One option is making the parameters of the GEV models time-dependent




• Among others, a user-friendly R-based toolkit (extRemes) is available from

http://www.assessment.ucar.edu/toolkit

(Stephenson and Gilleland, 2006; Gilleland and Katz, 2005)






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EURANDOM & KNMI, May 2009Kharin et al., J.Climate, 2007


• For providing information services on changing climate extremes the combined use of different techniques is recommended, as this will also provide information on the uncertainties

Take home message


• For providing information services on changing climate extremes the combined use of different techniques is recommended, as this will also provide information on the uncertainties

• New infrastructural works should be designed on the basis of both historical information on changes in extremes and projected future changes

Take home message


the end

EURANDOM & KNMI, May 2009http://eca.knmi.nl




Alexander et al.,2006; in IPCC-AR4

Documents

Analysis of extremes in a changing climate in support of informed decisions for adaptation