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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. Topics. ECA&D project Approach to homogeneity Results, Conclusions. ECA&D project.

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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


Topics

  • ECA&D project

  • Approach to homogeneity

  • Results, Conclusions


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


Current participation

  • Most data from 1900 up to 2001

  • More than 200 stations

  • Tmin, Tmax, Tmean,

  • precipitation amount, pressure


Trend analysis of extremes requires:

A dense, high-resolution, accurate and consistent dataset


Method

Homogenization of daily series

Instead: labelling of series

-> confidence for trend and variability analysis


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


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)


vDTR

DTRi:Diurnal temperature Range for day i in a specific year

M: number of days in the year


Classification

  • Labels:

    • Useful (0/1 tests significant)

    • Doubtful (2 tests significant)

    • Suspect (3/4 tests significant)


Station Groningen (NL)

1948: change of observation hut

1951: relocation

1959: change in sensor height


Station Groningen (NL)

Buishand Range, Pettitt and Von Neumann significant -> ‘suspect’


Temperature 1946-1999

mDTR

vDTR

->54% ‘suspect’, breaks (partly) supported by metadata


Precipitation 1946-1999

Number of wet days

Paper: International Journal of Climatology,

May, 2003

-> 10% ‘suspect’


Conclusions

  • 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


And…

  • further investigations to test homogeneity on daily basis

  • MASH method used for homogenization on monthly ECA&D series


More info at: http://www.knmi.nl/samenw/eca


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