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European Climate Assessment & Dataset
Judging homogeneity of daily series Fourth seminar for homogenization Budapest, 6-10 October 2003 Janet Wijngaard, KNMI, the Netherlands
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Topics ECA&D project Approach to homogeneity Results, Conclusions
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ECA&D project data analysis focusing on observed changes in extremes
gather daily series of observations at meteorological stations in Europe and the Middle East quality control and homogeneity analysis of the series dissemination of data and analyses results
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Current participation
Most data from 1900 up to 2001 More than 200 stations Tmin, Tmax, Tmean, precipitation amount, pressure Success is afhankelijk van deelname van de participanten!
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Trend analysis of extremes requires:
A dense, high-resolution, accurate and consistent dataset
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Method Homogenization of daily series Instead: labelling of series
-> confidence for trend and variability analysis
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Two-step approach Four homogeneity tests applied to ECA dataset to identify potential inhomogeneities in annual resolution testing variables representative for the daily resolution Grouping of results -> overall classification
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Homogeneity tests and variables
Tests (absolute): SNHT Buishand Range Pettitt Von Neumann Ratio Variables: precipitation: number of wet days temperature: mDTR and vDTR (annual mean of absolute day-to-day differences of DTR)
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vDTR DTRi: Diurnal temperature Range for day i in a specific year
M: number of days in the year
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Classification Labels: Useful (0/1 tests significant)
Doubtful (2 tests significant) Suspect (3/4 tests significant)
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Station Groningen (NL)
1948: change of observation hut 1951: relocation 1959: change in sensor height
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Station Groningen (NL)
Buishand Range, Pettitt and Von Neumann significant -> ‘suspect’
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Temperature mDTR vDTR ->54% ‘suspect’, breaks (partly) supported by metadata
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Precipitation 1946-1999 Paper: International Journal of Climatology,
Number of wet days Paper: International Journal of Climatology, May, 2003 -> 10% ‘suspect’
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Conclusions most severe step-wise breaks are detected
most severe step-wise breaks are detected metadata support for detected breaks essential no homogenizing of daily series labelling system good basis for series selection in trend analysis
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And… further investigations to test homogeneity on daily basis
further investigations to test homogeneity on daily basis MASH method used for homogenization on monthly ECA&D series
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More info at: http://www.knmi.nl/samenw/eca
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