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European Climate Assessment & Dataset Judging homogeneity of daily series

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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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Presentation Transcript
slide1

European Climate Assessment & Dataset

Judging homogeneity of daily series

Fourth seminar for homogenization

Budapest, 6-10 October 2003

Janet Wijngaard, KNMI, the Netherlands

slide2

Topics

  • ECA&D project
  • Approach to homogeneity
  • Results, Conclusions
slide3

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
slide4

Current participation

  • Most data from 1900 up to 2001
  • More than 200 stations
  • Tmin, Tmax, Tmean,
  • precipitation amount, pressure
slide5

Trend analysis of extremes requires:

A dense, high-resolution, accurate and consistent dataset

slide6

Method

Homogenization of daily series

Instead: labelling of series

-> confidence for trend and variability analysis

slide7

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
slide8

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)
slide9

vDTR

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

M: number of days in the year

slide10

Classification

  • Labels:
    • Useful (0/1 tests significant)
    • Doubtful (2 tests significant)
    • Suspect (3/4 tests significant)
slide11

Station Groningen (NL)

1948: change of observation hut

1951: relocation

1959: change in sensor height

slide12

Station Groningen (NL)

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

slide13

Temperature 1946-1999

mDTR

vDTR

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

slide14

Precipitation 1946-1999

Number of wet days

Paper: International Journal of Climatology,

May, 2003

-> 10% ‘suspect’

slide15

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
slide16

And…

  • further investigations to test homogeneity on daily basis
  • MASH method used for homogenization on monthly ECA&D series