Thomas C. Peterson,National Climatic Data Center, National

Oceanic and AtmosphericAdministration, Asheville, NorthCarolina, USA, and Chair, WMO

Commission for Climatology OpenProgramme Area Group on the

Monitoring and Analysis of ClimateVariability and Change

Introduction

For decades, most analyses of long-term global climate change usingobservational data have focused onchanges in mean values. Several well-respected datasets of monthly stationtemperature and precipitation dataprovide quite good coverage acrossthe globe. Analysing changes inextremes (e.g. the number of daysexceeding the 90th percentile of mini-mum temperature observations),however, requires long-term digital

daily data. Unfortunately, such data arenot readily available internationally forlarge portions of the world. In the 2002“global” analysis by Frich et al. (2002),almost no analysis of extremes waspossible for most of Central and SouthAmerica, Africa and southern Asia.However, a concerted series of effortsto remedy that situation is underway.

Role of an international expertteam (ET)

Two complementary efforts to enableglobal analysis of extremes are beingcoordinated by the joint WMOCommission for Climatology (CCl)/World Climate Research Programme(WCRP) Climate Variability andPredictability (CLIVAR) project’s ExpertTeam on Climate Change Detection,Monitoring and Indices (ETCCDMI).Detailed information on the ET is available at http://www.clivar.org/organization/etccd. Members of theExpert Team come from all continentsand encompass a wide range ofexpertise in the field of climatechange. The author is not a member ofthe ET but works closely with it aschair of the CCl Open ProgrammeArea Group (OPAG) on the Monitoringand Analysis of Climate Variability andChange to which the ET belongs. Asall ET members are volunteers withfull-time jobs, the focus of their workmust be on what they can coordinate,recommend or inspire, rather than dothemselves.

One of the ET’s activities is interna-tional coordination of a suite of climate-change indices derived from daily datawhich focus primarily on extremes. Thedevelopment of the indices involvesnot only ET members but also numer-ous other scientists working with dailyclimate data. By setting an exactformula for each index, analyses donein different countries or differentregions can fit together seamlessly.

A total of 27 indices are considered tobe core indices. They are based on dailytemperature values or daily precipita-tion amount. Some are based on fixedthresholds that are of relevance toparticular applications. In these cases,thresholds are the same for all stations.

Other indices are based on thresholdsthat vary from location to location. Inthese cases, thresholds are typicallydefined as a percentile of the relevantdata series. The definitions of the27 indices and the formulas for calcu-lating them are available fromhttp://cccma.seos.uvic.ca/ETCCDMI.This Website also provides theFORTRAN code for calculating theindices from daily data and a user-friendly software package to calculatethe indices. This software package,called RClimDex, uses the free soft-ware R (see http://www.r-project.orgfor more information), which is alanguage and an environment for statis-tical computing and graphics.

Analysis software does not, however,perform without data. In many parts ofthe world, enough daily data havebeen digitized to contribute to ananalysis but institutions are reluctantto share them. This is a difficult prob-lem to address. The solution proposedby the ETCCDMI’s predecessor was tohold regional climate-change work-shops modelled after the Asia PacificNetwork workshops (Manton et al.,2000; Peterson et al., 2001). Two wereheld in 2001 and, in view of the expe-rience gained, the ETCCDMI decidedto hold a series of other such work-shops to cover all areas of the globe.

Regional workshop concept

The workshops bring together partici-pants from as many countries aspossible across an area for a combina-tion of seminars and hands-onanalyses of the daily data they bring

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with them. Through this process, aworkshop “recipe” has been created.The workshops start with overviewseminars, describing the reasons forholding the workshops and how theclimate of the region is projected tochange. The participants then describethe climate of their countries and thestation data they bring with them.

The hands-on analysis starts with qual-ity control (QC). RClimDex has severalQC checks. Some identify specific datapoints as outliers. For these tests, eachdata point that is potentially a problemis examined. Based on data before andafter, as well as the understanding ofthe climate of the region, the data areedited if the problem is obvious (e.g.182° changed to 18.2°); set to missingif it is clearly a problem with unknownsolution; or kept if deemed probablyvalid. With each change or acceptanceof an outlier, a record of the decisionand the reasons behind it is made inthe QC log file. The second stage ofQC involves evaluating numerousdetailed graphs of daily data to detectevidence of possible quality issueswith the data. An example of thiswould be an impossibly long period oftime with zero precipitation. This prob-lem can arise because many countriesdo not record zero precipitation, somissing values must initially beassumed to be zero.

The next stage of analysis is to conducthomogeneity assessments. Homo-geneity adjustments of daily data arecomplex and difficult to make well(Aguilar, 2003). The focus on homogene-ity is therefore to identify significantproblems. When the homogeneity-testing software identifies a likely prob-lem, the participant consults stationhistory metadata, if available, to under-stand why. Non-climatic jumps in thetime series have resulted in somestations not being used in the indicesanalyses or used only for the period afterthe discontinuity.

Once QC and homogeneity testinghave been accomplished, the calcula-tion of the indices is quite simple. Oneof the benefits of doing this at aregional workshop is the synergy ofimmediately being able to see howresults compare across borders. Theparticipants create a short presenta-tion of what the analysis is indicatingabout changes in extremes for eachcountry. Similar results that span coun-try borders verify the robustness of

the analysis. Participants have foundthis workshop product quite usefulwhen they return home.

The last part of the workshop looks tothe future. This includes user feedbackand advice for future workshop organ-izers. Discussing how to improve theavailable Global Climate ObservingSystem (GCOS) Surface Network(GSN) data, now that the participantsclearly understand the value of beingable to compare analyses across coun-try borders, is also relevant. Lastly, theparticipants discuss how to make theresults of the analyses started at theworkshop useful for climate-changeassessments. This includes decidingwho will lead the writing of multi-authored peer-reviewed journalarticles, making the time-series of theindices available to other researchers,and the data themselves available toother researchers (the author listincludes all participants who bring datacontributing to the analysis).

So far, none of these workshops hasbeen able to release time-series ofdaily data. There has been greatsuccess, however, in reaching agree-ment to release the indices and somesuccess in encouraging the release ofdata from GSN stations to the GSN

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The work described in thisarticle is the result of thecollaborative effort of manyindividuals, who have beensupported in this endeavourby their home institutions.Unfortunately, they are toonumerous to be mentionedhere by name. WMO,through its Expert Teams,provides the structure andcoordination so that thesevolunteers may make theseaccomplishments.

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Archive Centre. For each of theseseries of workshops, peer-reviewedjournal articles on changes inextremes in the regions are either inpreparation or have already beensubmitted and the indices preparedto contribute to the global indicespaper.

The workshops

The previous incarnation of theETCCDMI, a CCl/CLIVAR WorkingGroup, also addressed indices andregional climate change and held twoworkshops in 2001. The first was in theCaribbean, where 18 of the 21 NationalMeteorological Services participated.This workshop resulted in the releaseof daily data, indices, a meeting report,and a 17-author peer-reviewed journalarticle on how the climate in the regionis changing (Peterson et al., 2002). Thesecond workshop was held inCasablanca, Morocco, for variousAfrican countries (Easterling, 2003).

The ETCCDMI sought to improve andextend those workshops to covermore of the world. Financial supportwas a limiting factor but adequateresources have become available tohold five workshops.

Summary

This series of regional climate-changeworkshops is achieving severalimportant objectives. In regionswhere data are not readily accessible,a suite of climate-change indices thatfocus primarily on extremes has been

produced and made available. Theanalyses would gain increased credi-bility by being reproducible with therelease of the data. The strong focuson quality control and homogeneitytesting (the results of which are beingreleased), however, make it possibleto evaluate the analysis independ-ently, even without the digital data.

Training scientists in these countriesmay not have been the driving goal,but the workshops have definitely hada major capacity-building aspect, asoutside experts worked closely withregional participants on data analyses,provided them with user-friendlysoftware, and introduced them to afree statistical package. The capacitybuilding has, in turn, helped foster agreater appreciation of the importanceof long-term in situ data and this hasresulted in renewed efforts at

digitizing historical records, as well asfulfilling GSN data-exchange goals.

These workshops are making a clearcontribution to our understanding ofhow climate extremes are changingaround the world. In addition to the in-depth peer-reviewed regional papers,the indices analysed at each of theworkshops are contributing to twoglobal extremes papers. Thanks largelyto these workshops, these papers willindeed be global. Together, they willmake a significant contribution to theupcoming Fourth Assessment Reportof the Intergovernmental Panel onClimate Change.

Lastly, as one participant wrote afterthe Middle East workshop, they are “avery good beginning for regional co-operation”.

Acknowledgements

These workshops were made possible bythe generous financial support from the USState Department, the SysTem for Analysis,Research and Training, the World ClimateResearch Programme (co-sponsored byWMO, the International Council for Scienceand the Intergovernmental OceanographicCommission of UNESCO) and the Inter-American Institute for Global ChangeResearch.

Thanks are also due to the institutions whichhosted the workshops: the University of Cape

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Southern Africa

Cape Town, South Africa, 31 May-4 June 2004

Southern South America

Maceio, Brazil, 9-14 August2004

Middle East

Alanya, Turkey, 4-9 October2004

Central America and northernSouth America

Guatemala City, Guatemala, 8-12 November 2004

South-Central Asia

Pune, India, 14-19 February2005

The workshops

Regional workshops onclimate change indices are“a very good beginning forregional cooperation”.

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Town, South Africa; the Federal University ofAlagoa, Brazil; the Turkish StateMeteorological Service; the National Instituteof Seismology, Vulcanology, Meteorology andHydrology, Guatemala, and the RegionalCommittee for Water Resources of theCentral American Isthmus (Costa Rica); andthe Indian Institute of Tropical Meteorology(Pune)

References

AGUILAR, E., I. AUER, M. BRUNET,T.C. PETERSON and J. WIERINGA, 2003:Guidelines on Climate Metadata andHomogenization, WCDMP-No. 53,WMO-TD No. 1186. WMO, Geneva,55 pp.

EASTERLING, D.R., L.V. ALEXANDER,A. MOKSSIT, V. DETEMMERMAN, 2003:CCl/CLIVAR Workshop to DevelopPriority Climate Indices. Bull. Amer.Meteorol. Soc., 84, 1403-1407.

FRICH, P., L.V. ALEXANDER, P. DELLA-MARTA,B. GLEASON, M. HAYLOCK, A.M.G. KLEIN-TANK and T. PETERSON, 2002: Observedcoherent changes in climatic extremesduring the 2nd half of the 20th century,Climate Res., 19, 193-212.

MANTON, M.J., et al., 2000: Trends inextreme daily rainfall and temperaturein Southeast Asia and the SouthPacific: 1961-1998. Int. J. Climatol., 21,269-284.

PETERSON, T.C., C. FOLLAND, G. GRUZA,W. HOGG, A. MOKSSIT, and N. PLUMMER,2001: Report of the Activities of theWorking Group on Climate ChangeDetection and Related Rapporteurs,WMO/TD No. 1071,WMO, Geneva,146 pp.

PETERSON, T.C., M.A. TAYLOR, R. DEMERITTE,D.L. DUNCOMBE, S. BURTON,F. THOMPSON, A. PORTER, M. MERCEDES,E. VILLEGAS, R.S. Fils, A. KLEIN-TANK,A. MARTIS, R. WARNER, A. JOYETTE,W. MILLS, L. ALEXANDER, andB. GLEASON, 2002: Recent Changes inClimate Extremes in the CaribbeanRegion. J. Geophys. Res., 107(D21),4601, doi: 10.1029/2002JD002251(Nov. 16, 2002).

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