1. Upward trends in time series of basic characteristics of air temperature at selected meteorological stations in Slovakia AIR TEMPERATURE TRENDS AT SELECTED METEOROLOGICAL STATIONS AND TIME SERIES Pavol Faško 1 – Pavel Š ť astný 1 – Marek Švec 1 – Peter Kajaba 1 – Oliver Bochní č ek 1 (1) Slovak hydrometeorological institute Bratislava, Slovakia ABSTRACT Rise of the air temperature due to climate change in recent decades is very clear. When comparing the long-term average air temperature in the period 1951-1980 with the 1981-2010 period, the warming in the last thirty years was most noticable in January, May and summer months, while adequately to this average temperatures of individual seasons increased as well as the values of average annual air temperature. The period from March to September in 2012, was the warmest seven-month period in Hurbanovo from the beginning of meteorological measurements at this meteorological station since 1871. This fact was also reflected in other characteristics of the air temperature in Slovakia. The average monthly air temperatures in the last 25 years know represent the warmest months from the mid- 20th century. This is also reflected in the trends of the average monthly, seasonal and annual air temperatures, which are in the charts expressed by fourth degree polynomial. These tendencies weren’t recorded just within the warmest regions of southwestern Slovakia (represented by station Hurbanovo), but throughout its entire territory, including the high mountain locations (represented by station Lomincký štít). The year 2012 was one of the warmest years in the history of meteorological measurements in Slovakia, however in addition to a period with several months with above-average air temperatures, there was one particularly frosty short period during the end of January and in the first half of February 2012. This trend may indicate an increased risk of higher fluctuations of the air temperature in the future. Fig. 1 The average monthly air temperature in different months of the year at selected meteorological stations since 1951 The contents of the presented images show that in the time series of average monthly, seasonal and annual air the greatest rises in values ​​ of the average air temperature have been recorded since the beginning of the 90's of the 20th century. This trend is not the same in all months of the year and in all 4 seasons. Good examples are the months of November and December, in which the air temperature trend in Hurbanovo (but also at other locations within Slovakia) is rather indifferent. The rate of increase of average air temperature has approximately in the last two decades also some regional aspects. This increase is relatively less apparent in southwestern Slovakia and conversely it's more significant in the valleys of central Slovakia or in the eastern Slovakia. The effects of global warming before the last decade of the 20th century were definitely more significant in the southwestern regions of Slovakia than in the other regions of Slovakia. The winters in the valleys of central Slovakia, are more humid and warmer in the last decades than they were in the past, which means that in these regions, the amount of mixed and liquid precipitation of the total precipitation during the winter is growing. Decrease of snow cover was also registered in these areas and due to increased cloudiness and precipitation there are now less suitable conditions during winter, for the occurrence of strong night and morning frosts. On the other hand the cloudiness in these regions is lower in the summer, the amount of long-term rainfall is declining, which supports greater warming of these valleys. The end result is that the growth of average annual air temperature in these areas is greater, than it is for example on the Danube lowland. The same applies to eastern Slovakia, where the registered decrease of snow cover causes that conditions for cooling of air above the snow cover are now less common (temperature differences between winter and summer has become less significant). In 2012, the changes of temperature conditions in Slovakia were very interesting. The trends from the previous periods were confirmed to such extent that the average monthly air temperature in most months of the 2012 was again on the leading positions, in hierarchical order of monthly air temperature values ​​ since the year 1951 (Fig. 4). The time series of average annual air temperatures in Hurbanovo since 1871 show that the warmest year in this location so far was a year 2000, with an average annual air temperature of 12.1 °C (1961- 1990 temperature normal is 10.0 °C). Very interesting is the fact that the highest mean annual air temperature at the Slovakia’s highest mountain station - Lomnický štít (with air temperature measurements since 1940) was recorded in 2011. CONCLUSIONS REFERENCES Faško, P. – Lapin, M. – Pecho, J.: 20-year extraordinary climatic period in Slovakia. In Meteorological Journal, 11, č. 3, s. 99 – 105, obr. 14. Petrovič, Š. et al.: Klimatické pomery Hurbanova. IClimatic conditions at Hurbanovov). HMÚ, Praha, 1960, 278 s. The period from March to September in 2012 was the warmest such seven-month period beginning in Hurbanovo from meteorological measurements at the meteorological station in 1871. This fact is also reflected in other characteristics of the air temperature in Slovakia. The average monthly temperature in last 25-years warmest months are mostly from the mid-20th century. This was also reflected in trends in average monthly, seasonal and annual air temperatures, which were expressed quartic polynomial. Acknowledgment: This work was part of the project "Development of technology of spatial data processing of the climate system" ITMS 26220220102, and "Applied research of methods for determining the climatic and hydrologic design parameters", ITMS 26220220132 funded from the EU Structural Funds Fig. 2 The average air temperature in summer (June-August) and winter (December-February) at selected meteorological stations since 1951 Fig. 3 The average annual air temperature at selected meteorological stations since 1951 Fig. 4 Ten warmest and ten coldest months since 1951 at selected meteorological stations (*months of the last 25 years are marked by red color) Fig. 5 Avearege air temperature [°C] in the period from march to september in the years 1871-2012 at meteorological station Hurbanovo