Homogenization of mean monthly temperature time series of Greece

During the last decades due to the increased interest about climate change, many studies have been conducted trying to detect shifts in climatic series. The necessity of the homogenization of meteorological observations becomes obvious to all these studies. In practice, inhomogeneities are hardly ever avoided, because the meteorological station networks are constantly changing. A myriad of methods for detecting and adjusting inhomogeneities in climate series have been developed. In this study two homogeneity methodologies, namely MASH and Climatol, were applied to 49 monthly temperature series of synoptic stations, covering almost all climatic zones of Greece, belonging to the operational weather network of the Hellenic National Meteorological Service ( HNMS ). Time series cover periods ranging from 35 to 45 years. Only 8.2% of the stations passed both tests successfully, another 10.2% passed the MASH homogeneity test successfully without any breakpoint, but not the Climatol test. On the other hand, 14.3% of the stations passed the Climatol test successfully but not the MASH test. The remaining stations presented one or more breaks or outliers in both homogeneity methods. Due to lack of metadata only 15% of the breaks could be explained by the stations' history. Station relocations as well as changes in observation practices caused most of the temperature anomalies. The adjustments in seasonal series were in the range from −2.54 to 1.39 °C for MASH and from −2.30 to 1.50 °C for Climatol. Seasonal and annual mean temperature trends were analyzed and their statistical significance calculated. The most pronounced seasonal trends were recorded in summer. Also, the differences of climatological normals for the period 1961–1990 between raw and homogenized annual series were computed. The absolute values of differences ranged from 0.0 to 0.8 °C for MASH and from 0.0 to 1.0 °C for Climatol.