Homogenisation of mean air temperature time series from Vojvodina (North Serbia)

Abstract

Standard Normal Homogeneity Test (SNHT) was applied for the detection of inhomogeneities in the time series of mean monthly air temperature data for 7 stations in Vojvodina Province (North Serbia) for the period 1949-2010. In time series of two stations missing data have been found, but gaps do not exceed 5% of dataset. These gaps have been filled in with values from the three best correlated neighbouring stations. Seven series of the moving average multi-annual air temperature (48-month and 72-month span) have been investigated. For inhomogeneity detection of these time series AnClim software package has been used, while further analysis used various statistical and cartography methods. Reference series have been chosen from 4 to 6 stations, based on distance, similar altitudes and squared correlation coefficient higher than 0.9. SNHT has been applied for detecting abrupt homogeneity breaks. The critical level of the test was 95%. Detected break points were compared to metadata records in order to diagnose causes of featured inhomogeneities. That type of information was crucial for applying calculated corrections of investigated series. After the homogenisation process, the adjustment values have been analysed. The breaks which are explained in metadata are related to the relocations of the stations and show mostly low correction values. Differences between average values of raw and homogenised monthly time series are mostly within range from 0 to 0.12°C. According to low difference data, the results present very similar linear trends of original and homogenised time series for all stations. Still, there are a substantial changes of spatial distribution paterns. The patterns for homogenised series seem more regular, due to successful application of homogenisation process, making the image of climate variations in Vojvodina more reliable.