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Homogenisation of temperature time series in Croatia

Homogenisation of temperature time series in Croatia. Dubravka Rasol, Tanja Likso, Janja Milković. Meteorological and Hydrological Service of Croatia. Outline. Homogenisation in Croatia Croatian meteorological stations network

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Homogenisation of temperature time series in Croatia

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  1. Homogenisationof temperature time seriesin Croatia Dubravka Rasol, Tanja Likso, Janja Milković Meteorological and Hydrological Service of Croatia

  2. Outline • Homogenisation in Croatia • Croatian meteorological stations network • MASH and SNHT methods applied to Croatian data and the comparison of the results • Closer look - Karlovac temperature time series

  3. Homogenisation in Croatia • Carried out only sporadically (B. Volaric 1982, G. Galekovic 1995, T. Likso 2004) • K. Pandzic: homogenisation of 22 temperature series for the Climate Atlas needs – modified SNHT method – to be published • Joining the HOME COST Action ES0601 (2007-2011) • Bilateral cooperation with the Hungarian Meteorological Service –the homogenisation issue (2007-2009)

  4. Croatian meteorological stations network Temporal distribution of all meteorological stations

  5. Croatian meteorological stations network Spatial distribution of main and climatological stations 41 main meteorological stations 116 climatological stations 336 precipitation stations some with more than 100 years of observations 2 upper-air stations 8 radar stations 34 automatic stations

  6. Temperature series chosen for analysis Monthly mean air temperature series 9 stations from the NW part of Croatia Bjelovar Karlovac Koprivnica Krizevci Sisak Slavonski Brod Zagreb Gric Zagreb Maksimir Varazdin Period: 1961 - 2006

  7. MASH and SNHT method Both methods are for relative homogeneity testing MASH – Multiple Analysis of Series for Homogenisation (Szentimerey, 1994) • Reference series do not need to be homogeneous • Mutual comparisons of series within the same climatic area • Weight factors of reference series based on distance from the test series • Software: MASH 3.02 (Many thanks to Tamas!) SNHT – Standard Normal Homogeneity Test (Alexandersson, 1986) • Ideally, reference series should be homogeneous • Likelihood ratio test • Weight factors of reference series are correlation coefficients • Software: AnClim (Stepanek, 2005)

  8. Breakpoints detected by MASH and SNHT

  9. MASH and SNHT homogenised temperature series

  10. 1981 1991 MASH and SNHT homogenised temperature series

  11. 1992 2001 MASH and SNHT homogenised temperature series

  12. MASH and SNHT differences

  13. Karlovac Huge inhomogeneity! Two breakpoints detected by both methods - both in accordance with metadata: • 1992 - relocated from the urban to the suburban area • 2001 - moved around 50 m

  14. Karlovac Differences between yearly mean temperatures at Karlovac station and at all the reference stations 1992 2001 differences (°C) year

  15. Karlovac y = 0.0108x + 10.645 y = 0.0316x + 9.3661

  16. Conclusions • Both MASH and SNHT methods detected all breakpoints known from metadata, as well as additional ones. • The differences between homogenised series obtained by each method were negligible. The question is what to do with the Karlovac series: • Is it better to divide it in two series or to homogenise it?

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