1. Homogenisation of temperature time series in 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 ( )
Bilateral cooperation with the Hungarian Meteorological Service – the homogenisation issue ( )

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:

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
Bjelovar
Karlovac
Koprivnica
Krizevci
Sisak
Slavonski Brod
Zagreb Gric
Zagreb Maksimir
Varazdin

9. MASH and SNHT homogenised temperature series

10. MASH and SNHT homogenised temperature series
1981
1991

11. MASH and SNHT homogenised temperature series
1992
2001

12. MASH and SNHT differences

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

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

17. Karlovac
y = x
y = x

18. 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?