Tendencies of climatic extremes occurrence in different Moravian regions and landscape types

MUŽIKOVA, B. , VLCEK, V. , STŘEDA, T. : Tendencies of climatic extremes occurrence in diff erent Moravian regions and landscape types. Acta univ. agric. et silvic. Mendel. Brun. , 2011, LIX, No. 5, pp. 169–178 In this study present frequency of several characteristic days as tropical, summer, arctic, frost and ice days and also length of heat waves was compared with modelled future occurrence of these climate extreme indices. Climate-diagrams were used for drought hazard assessment. The main objective of our research was to detect possible changes of frequency of the extreme events toward future. Data from four localities in the Czech Republic (Moravia) were chosen for the evaluation. Each locality represents diff erent climatic, landscape and settlement conditions. Localities are represented by the closest grid points. Future trend was modelled for scenario data (scenario A1B) by regional model ALADIN-Climate/CZ in the Czech Hydrometeorological Institute. The results showed obvious rising tendency of tropical and summer days frequency on all localities, especially in lowland regions. Very strong decreasing trend seemed to be in occurrence of arctic days, which might be very scarce in the future. Frost days and ice days should also decrease. Increase in number of days in heat wave was considerable. Climate-diagrams showed possible rising drought hazard for all localities towards future periods. characteristic days, climatic extremes, ALADIN Extreme climatic events can have serious impact on environment and society. Analyses of observed temperature in many regions of the world have already shown some important changes in the extremes occurrence. The extreme climatic events are mainly associated with precipitation and temperature. Global air temperature has increased by an average of 0.74 °C (IPCC 4th Assessment Report 2007) in last hundred years. Generally, the global daily minimum and maximum air temperature values (Tmin and Tmax) increase, though the minima increase three times faster (Kejna et al., 2009). The negative consequences of possible climate change are rather connected with changes in variability and occurrence of extreme events than with changes in average temperature characteristics. The research of tendencies of several climatic extreme indices has been realized in many countries all over the world. A study of the longterm changes of various climatic extremes was made jointly by a number of European countries. It was found that the changes in maximum and minimum temperatures follow the corresponding welldocumented mean temperature changes. Minimum temperatures, however, have increased slightly more than maximum temperatures, although both have increased. As a result, the study confi rmed that the diurnal temperature range has mostly decreased during the present century in Northern and Central Europe. Frost has become less frequent (Heino et al., 1999). Not only changes in average or minimum and maximum air temperature are suitable to study changes of climatic conditions. Characteristic days (tropical, summer, ice, frost and arctic days) are also very useful indices. A research focused on such temperature characteristics was also done in Canada. Vincent and Mekis (2006) studied trends and variations in several 170 B. Mužikova, V. Vlcek, T. Středa indices of daily and extreme temperature (frost days, cold days, cold nights, summer days, warm days, warm nights) and precipitation in Canada for the periods 1950–2003 and 1900–2003, respectively. Trends temperature extremes for South America during 1960–2000 are presented by Vincent et al. (2005). The results showed changes in temperature extremes in South America. Signifi cant trends were observed in the indices based on daily minimum temperatures. The percentage of cold nights is decreasing while the percentage of warm nights is increasing, and these changes are more pronounced during the summer (DJF) and fall (MAM). The night time warming corresponds to a signifi cant decrease in the diurnal temperature range over the continent. The results generally agree with what has been observed in many other parts of the world. The near global analysis by Frich et al. (2002) has indicated an increase in the frequency of warm nights, a decrease in the extreme temperature range, and also a decrease in the number of frost days. Frost days is not a representative index for South America since the temperature remains above 0°C almost everywhere with the exception of the stations located in the high mountains of Ecuador, Peru, and Bolivia, and for those stations located in the southern part of Argentina and Chile. The results from the Caribbean region have indicated that the frequency of warm nights and warm days has signifi cantly increased since the late 1950s while it seems that in South America only the warm nights have increased. Temperature and precipitation extremes were studied also in many Asian countries. Changes in indices of climate extremes in central and south Asia were studied by Klein Tank et al. (2006). At 70 per cent of the stations, statistically signifi cant increases in the percentage of warm nights/days and decreases in the percentage of cold nights/days were observed for the period 1961–2000. In the conditions of Czech Republic temperature extremity was evaluated by Pokladnikova et al. (2008). Three stations in south Moravia in elevation about 200 m a.s. l. Every month of the period 1961– 2007 was included to defi ned category of extremity (extraordinary above normal, very above normal, above normal, normal, below normal, very below normal and extraordinary below normal). As extraordinary above normal 79 months, as very above normal 115 moths, as above normal 175 were classifi ed. As extraordinary below normal 32 months, as very below normal 86 and as below normal 129 were classifi ed. Periods of 1961–1970 and 1971–1980 contains more cold months than last two periods (with prevails warm month). Hot weather and changes in precipitation already express themselves in various sectors and regions, for example in agriculture. Very undesirable eff ect of climate extremes is drought. Drought events may occur in case of long-term lack of precipitation coinciding with hot weather. Analysis of several temperature and precipitation indices and their changes in the second half of the 20th century in Hungary with emphasis on agriculture was done by Pongracz et al. (2006). Their results showed that regional intensity and frequency of extreme precipitation increased, while the total precipitation decreased in the region and the mean climate became drier. Recently a few episodes of heat waves have been observed in European countries, especially in Mediterranean region. Some of them were connected with hundreds of human death cases (from hyperthermia and heart failure). Severe heat waves have caused catastrophic crop failures. Anyway they mean stress for humans, animals and plants. The research of heat waves duration has been done mainly in urban areas, especially in big agglomeration. In Czech Republic occurrence of heat waves and tropical days was evaluated by Středova et al. (2010) and Kyselý (2003). Most of the research has been done for the present and past. Modelling the tendencies of climatic extremes is quite rare, but defi nitely not uninteresting and unimportant because of the management planning in various economy sectors. The uncertainty of future climate change trends arises from the ignorance of future development of emissions and greenhouse gases concentration (and also aerosols that have cooling eff ect). That is why the models work with emission scenarios with a wide range – from low to high emissions. Four main groups of emission scenarios of possible development of society and climate till the end of 21st century were established within the frame of the Intergovernmental Panel on Climate Change. A1 Scenario is a group of scenarios that describes the world with a very fast economy growth and new technologies development. A1B is a subgroup which was used in this paper. This scenario represents a state with balance in use of all fuels (fossil and other fuels). MATERIALS AND METHODS