COSTOC-2006-32

Olivier Mestre Météo-France FranceIngebor Auer ZAMG AustriaEnric Aguilar U. Rovirat i Virgili SpainPaul Della-Marta MeteoSwiss SwitzerlandVesselin Alexandrov NIMH BulgariaSylvie Jourdain Météo-France France

ADVANCES IN HOMOGENISATION METHODS OF CLIMATE SERIES:

AN INTEGRATED APPROACH

COSTOC-2006-32

Homogenisation : WHY?Exemple of PAU-UZEIN temperatures

• Juin 1912 PAU-LESCAR (EN) • 2005 PAU-UZEIN (AERO)

COSTOC-2006-32 Station SilistraStation Silistra

COSTOC-2006-32 Station DobrichStation Dobrich

COSTOC-2006-32

Anomalies of annual minimum temperature in Anomalies of annual minimum temperature in Kjustendil (raw data)Kjustendil (raw data)

COSTOC-2006-32

Raw series of annual Maximum Temperatures (TX) PAU-UZEIN

COSTOC-2006-32

Homogenisation of Pau Maximum Temperatures

• « before » • « after »

COSTOC-2006-32

Decomposition of climatological seriesDecomposition of climatological series

COSTOC-2006-32

Usual method: relative homogeneity

PRINCIPLE : removing the climatic signal to put into evidence artificial shifts in the series

minus

Tested series

Reference series

COMPARISON

series

COSTOC-2006-32

Two problems

• DETECTION OF SHIFTS

• CORRECTION OF SHIFTS

COSTOC-2006-32

Many solutions !

• DETECTIONVisual, Craddock test, Student t-test, Likelihood ratio test (SNHT), Potter test, Bayesian procedures, Local contrast test, Pettitt test, penalized likelihood, MASH…

• CORRECTIONComposite reference series, interpolated reference series, multiple non-homogeneous series (MASH), ANOVA (Mestre)…

COSTOC-2006-32

Statistical problems

• Related to detection

power and level of the procedures, which are the best ones?

• Related to correction

how to ensure unbiased corrections?

COSTOC-2006-32

Practical problems

• Data requirements, depending on parameters: spatial correlation

• Nature of correction: raw monthly estimated coefficients, annual coefficients?

• What about close shifts?• What about gaps?• Trust metadata or statistics?• Trust relative homogenisation or parallel measurements?

COSTOC-2006-32

Why COST?

• Many procedures, many authors, that might lead to different results

• Few intercomparisons

COST is an ideal platform for the exchange of experiences, harmonisation of approaches and

the development of joint methods

COSTOC-2006-32

Objectives

To achieve a general method for homogenising climate and environmental datasets

• Provide practical rules for the implementation of homogenisation.

• Provide tools for comparison and evaluation of different methods.

• Analyse the strengths and weaknesses of the methods for different applications.

• Provide methods for evaluating uncertainties resulting from homogenisation.

COSTOC-2006-32

Scientific Program

• Inventory of existing detection and correction methods• Compilation of a benchmark dataset to be used across the

Action• Selection, comparison and evaluation of existing detection

methods• Selection, comparison and evaluation of existing

correction methods• Documentation of practical recommendations• Selection, comparison and evaluation of existing

correction methods for daily data• Presentation and release of the new common method

COSTOC-2006-32

Is this ambitious?

YES

COSTOC-2006-32

Why ?

• Because we want to make a synthesis of the most appropriate methods, based on objective comparisons and sharing of practical experiences

• Because we feel that the corresponding software has to be released – just editing recommandations would be useless

COSTOC-2006-32

Is this TOO Ambitious?

NO

COSTOC-2006-32

Why ?

• We have a clear view of what has to be done• Benchmark dataset conception (simulated and

real cases)• Coding and testing the procedures is rather easy,

and may be done by students• To test real cases and edit practical

recommandations, we get together highly trained climatologists

COSTOC-2006-32

Structure of the proposal

• Working groups

WG1inventory

WG3Correction

WG2Detection

WG4Daily values

WG5Implement

Benchmark

Benchmark

Benchmark

Report

Report

Report

Report

Report

Method

Final report

Software

COSTOC-2006-32

Dissemination plan

• Mailing list: costh@meteo.fr

• Web site: domain name « homogenisation.org » is available, with free software and documentation

• Publications

• Workshops

• Training sessions (ENM)

COSTOC-2006-32

Benefits

• Standardisation of homogenisation procedures in Europe

• Results of climate studies based on homogenised series could be easily compared

• Provide a benchmark dataset that can be used to test future methods

• Significant advances in daily data homogenisation• All this will result in an increased confidence in

European (and global) assessments of mean and extreme Climate Change

COSTOC-2006-32

Benefits

• Links to European projects : CIRCE, MACE, ECA&D…

• Economical impacts: risk assessment (extremes: insurance companies)

• Calibration of weather derivatives

COSTOC-2006-32

Participants

• From 17 countries

• Around 60 participants– 60% plan to participate actively to the Action– 40% are mainly interested by the results– 45% may have students working on the Action

COSTOC-2006-32

Conclusion

• Many procedures

• Few intercomparisons

• Daily data correction has to be developed

Need of a COST concerted Action