INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 29: 223–242 (2009) Published online 23 May 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/joc.1718 Climate fluctuations in the Czech Republic during the period 1961–2005 Rudolf Br´ azdil, a * Kateˇ rina Chrom´ a, a Petr Dobrovoln´ y a and Radim Tolasz b a Institute of Geography, Masaryk University, Kotl´ aˇ rsk´ a 2, 611 37 Brno, Czech Republic b Czech Hydrometeorological Institute, Na ˇ Sabatce 17, 143 06 Praha 4- Komoˇ rany, Czech Republic ABSTRACT: This article addresses climatic fluctuations in the Czech Republic in the period 1961–2005. On the basis of data collected at 23 climatological stations, the fluctuations in monthly, seasonal, and annual series of selected climate variables, homogenized by means of Standard Normal Homogeneity Test (SNHT) (after Alexandersson), are analysed. With almost unchanging temperature continentality expressed by the Gorczy´ nski index, the annual series of mean air temperature, maximum and minimum temperature, daily temperature range, and sunshine duration all exhibit a rising linear trend, in contrast to dropping trends in relative air humidity, number of days with snow cover, and mean wind speed. There are no pronounced changes in precipitation totals, although their distribution over the course of the year becomes more regular in terms of the Markham seasonality index. Temperature trends, with the exception of autumn, show a clear enhancement since the 1980s; statistically significant rising trends occur for only spring, summer and the year in a good agreement with the Northern Hemisphere series. Linkage to fluctuation in the North Atlantic Oscillation Index (NAOI) is best expressed by the Czech temperature characteristics for January, February, and winter (in similar fashion to that for the number of days with snow cover), which can be ascribed to intensification of the western airflow over Central Europe. On the other hand, linkage to NAOI for precipitation is essentially weaker, because of the role of synoptic processes in influencing the occurrence of precipitation at the regional scale. Better relationships for temperature variables and wind speed are obtained if the Central European Zonal Index (CEZI) is used instead of NAOI as an indicator of circulation patterns in Central Europe. Copyright  2008 Royal Meteorological Society KEY WORDS climatic trends; climate variability; climate continentality; Czech Republic Received 13 June 2007; Revised 28 March 2008; Accepted 7 April 2008 1. Introduction The current process of global warming is one of the most significant factors affecting the development of the natural environment at local, regional, and global scales, with impacts upon human society and all its activities. It is ascribed to an intensification of the greenhouse effect arising out of an increase in concentrations of the greenhouse gases associated with anthropogenic activity (Houghton et al., 2001; Braganza et al., 2004; Klein Tank et al., 2005; Solomon et al., 2007). Over the past 100 years (1906–2005), the global temperature rise has reached a value of 0.74 ° C (Solomon et al., 2007) which, contrary to the preceding IPCC report (Houghton et al., 2001), means an intensification of warming by 0.14 ° C, because the temperature rise in the period 1901–2000 reached a value of 0.6 ° C. A long- term air temperature rise is also evident on the scale of the Czech Republic. Thus in the mean temperature series for the Czech Republic determined for the period 1848–2000, the statistically significant linear trend for the year reached 0.69 ° C/100 years and for the annual * Correspondence to: Rudolf Br´ azdil, Institute of Geography, Masaryk University, Kotl´ aˇ rsk´ a 2, 611 37 Brno, Czech Republic. E-mail: brazdil@sci.muni.cz period it varied between 0.36 ° C/100 years for summer and 0.93 ° C/100 years for winter (Br´ azdil and Kirchner, 2007). These values may be markedly higher at individual stations. Previous studies of climatic fluctuation in Central Europe have centred upon the analysis of air temperatures and precipitation (e.g. Br´ azdil et al., 1995, 1996, 2001; Rapp, 2000; B¨ ohm et al., 2001; Domonkos and Tar, 2003; Domonkos et al., 2003; Klein Tank and K¨ onnen, 2003; Matulla et al., 2003; Degirmendˇ zi´ c et al., 2004; Jones et al., 2004; Mi¸ etus and Filipiak, 2004; Piˇ soft et al., 2004; Auer et al., 2005; Begert et al., 2005; Casty et al., 2005; Chl´ adov´ a and Kalvov´ a, 2005; Hundecha and B´ ardossy, 2005; Moberg and Jones, 2005; Maier et al., 2006; Moberg et al., 2006; P´ ısek and Br´ azdil, 2006; Scherrer et al., 2006; Wulfmeyer and Henning- M¨ uller, 2006; Beniston, 2007; Chl´ adov´ a et al., 2007); some attention has also been paid to other meteorological elements like snow cover, sunshine, cloudiness, and hail- storms (e.g. Br´ azdil et al., 1994; Falarz, 2002; Laternser and Schneebeli, 2003; Matuszko, 2003; Bednorz, 2004; Franke et al., 2004; Lapin, 2004; Scherrer et al., 2004; Chrom´ a et al., 2005; Huth and Pokorn´ a, 2005; Scherrer and Appenzeller, 2006; Auer et al., 2007). Great atten- tion was also devoted to the study of temporal variability Copyright  2008 Royal Meteorological Society