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Frost Indexes for the Cold Half-year in the Czech Republic
Zahradníček, Pavel ; Rožnovský, J. ; Brzezina, J. ; Štěpánek, Petr ; Farda, Aleš ; Chuchma, F. ; Potopová, V.
The dynamics of air temperatures during cold half-year to a large extent affect all human activities. Most significant damages are caused by minimum air temperatures dropping to very low values. Due to the current ongoing climate change, air temperatures in winter in general are increasing, however, this does not necessarily mean the frequency of these very low temperatures decreases. It is not easy to express the course of air temperatures during cold periods using some simple characteristic. Meteorologists and climatologists use various characteristics, which can be referred to as frost indexes. These include the number of frost, ice or arctic days. Since these indexes not always perfectly reflect reaction of the nature to a particular temperature threshold, the analysis also included number of days with minimum air temperature below -3, -5, -7, -10, -15, -20 and -25°C. In the last 15 years (2001-2015), there has been a decrease in the frost indexes in comparison to the normal period 1961-1990, this trend however, is not always statistically significant. Significant changes were found in particular in case of the number of days with a higher temperature threshold (frost, ice days and minimum air temperature above -3 to -10°C). In contrast, days with extremely low temperatures are relatively rare (sometimes only observed once in several years), so the dominant factor here is rather variability. The paper also includes an analysis of possible future development based on the most recent climatological models.
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Determination and Changes in Winter Severity in the Period between 1961 and 2015
Zahradníček, Pavel ; Rožnovský, J. ; Brzezina, J. ; Štěpánek, Petr ; Farda, Aleš ; Chuchma, F. ; Potopová, V.
Values of the minimum air temperatures during cold periods, especially winter, have often negative impacts on a wide range of human activities. In the past there have been many cases when rapid decrease in air temperature caused damages to machines, halted traffic etc. Every winter or cold half-year can be assessed using several parameters. In this article, three climatological characteristics were used. First was the average air temperature. Second was the sum of effective air temperatures below 0°C and -5°C. Last characteristic, which determines the extremity of that particular period, is the absolute minimum air temperature. Space-time analysis was performed for all the three characteristics. Statistically, the most significant change was found in case of the average air temperature – there is a gradual warming since 1961. Air temperatures during winter are to a large extent affected by the continentality of the climate. In Bohemia, the warming is faster than in Moravia and the western part of the country has the lowest absolute minimum air temperatures. Using multiparametric analysis of climatological characteristics it was found that the coldest winter and coldest half-year from the analyzed years was in 1963. In contrast, mildest winter was in 2007. Current climatological models predict that winter temperatures by the end of 21st century will be higher by 2.4°C to 4.9°C, which would mean a significant change in the current winter conditions.\n
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Increase in Winter Air Temperatures in the Czech Republic between 1961 and 2010
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, Petr ; Zahradníček, Pavel
Based on the analysis of average monthly air temperatures between 1961 and 2010 it can be statistically proven that there is an increasing trend. The actual level of increase, however, is different for each season and is also specific for a particular region – there are differences between Bohemia and Moravia. In the summer, the average monthly air temperatures rise more significantly in Moravia, where there is a higher number of stations with increase of over 1°C compared to Bohemia. This is also true for the spring, for which the difference is not so profound, and is yet smaller in the autumn. In contrast, in the winter there is a more significant increase in Bohemia, where most stations show an increase of over 0.5°C. In Moravia the increase is usually only around 0.3 to 0.4°C. Differences between the increases of average air temperature can also be seen across the individual winter months. Highest increase was found in January, where some stations in Bohemia show an increase of over 1°C, a value that was not observed in Moravia, where some stations have an increase of less than 0.8°C. In December and February, the level of increase in general is much smaller. However, given the predicted increase of air temperatures in the future in general, it can be expected that in the upcoming decades the number of warm winters will increase. Such increase of air temperatures in the winter is likely to have negative impacts for the agriculture.
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Analysis of Frosts Observed in the End of April 2016 and the Associated Damages for Fruit Farming
Zahradníček, Pavel ; Rožnovský, J. ; Štěpánek, Petr ; Chuchma, F.
Air temperatures below 0°C, the so-called vegetation period frosts, have always been a problem in the climate conditions of the Czech Republic. The 2015/2016 winter as relatively mild, as well as the following beginning of spring and April. Major damages were caused by sudden rapid drop in air temperatures in the period between 25th and 30th April 2016, as a result of very cold air from the North. Air temperature began to fall on 19th April 2016, but only ground temperatures were below freezing point. Between 25th and 30th April, however, even air temperatures measured at 2m above the ground dropped below 0°C. All over the country, the minimum temperatures were below 0°C, usually between -2 and -4°C. The lowest minimum ground air temperatures were below -5°C at 85% of the area of the Czech Republic. In Moravia, the minimum ground air temperature was below 0°C on five days, in Bohemia it was every day in the period between 25th and 30th April 2016. It should be emphasized that during the flowering time of fruit trees without leaves, the flowers form an active surface. Due to radiation the flower temperature is often even lower than the measured ground air temperature minimum. This analysis does not include the effects of terrain, which determines positions of frost basins.
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The change of the rain factor on the net of stations in the Czech Republic during 1961-2010
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Precipitation totals do not express precisely the humidity conditions in the landscape. Therefore the Lang’s rain factor, constructed from monthly and annual average temperatures and precipitation totals on 267 stations in the Czech Republic during 1961-2010, has been used here. Its values are very different at different stations, the lowest they are at South Moravia and Labe lowlands. Its average for the whole territory displays a slow decrease during the 50 years, supplemented by strong fluctuations. The strongest decrease appears in the Northern boundary mountains. The same factor calculated only for summer displays stronger differences between highlands and lowlands, especially in South Moravian ones. Stronger decrease at North Moravia, especially in mountains, and very weak decrease at other parts takes place.
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Increase of annual and seasonal air temperatures in the Czech Republic during 1961-2010
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Using the monthly means of air temperatures at 267 stations in the Czech Republic, the long-term change has been estimated at each station for the last 50 years. Annual mean temperatures for the whole country show a considerable increase, more pronounced than that for global temperature, however, supplemented by strong fluctuations from year to year. Long-term changes in air temperatures at different stations and in different regions vary. Stronger increase in air temperatures can be seen in Bohemia, whereas in Moravia temperature increase is not so significant. This difference is more pronounced in the winter, whereas in the summer, the differences are smaller and perhaps of opposite nature. This means that the continentality of the climate in Moravia increases, while in Bohemia it very slightly decreases. Long-term changes depend only marginally on the absolute values of annual mean temperatures at the respective station. The increase of autumn temperatures is considerably lower than that of other seasons.
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The change of annual and seasonal precipitation totals in the Czech Republic during 1961-2012
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Using the monthly values of precipitation totals at 267 stations in the Czech Republic a longterm change has been estimated at each station for the last 50 years. Annual totals for the whole country display a slight increase, however, supplemented by a much stronger fluctuations from year to year. Long-term changes in annual totals at different stations and in different regions are different. In southern and western Bohemia precipitation totals increased more, in Elbe lowlands and in a large part of the Moravia, rather a small decrease in rainfall has been observed. Long-term changes depend only slightly on the total rainfall at the respective station or in the region. Summer precipitation totals increased more than annual averages, while spring precipitation totals decreased, at other times seasons the change is negligible. At the same time, the annual variation changes slightly: maximum precipitation has shifted from June to July and August.
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Influence of precipitation and temperature in the period 1961–2100 on the possibilities to grow Picea abies in the Czech Republic
Cudlín, Pavel ; Štěpánek, P. ; Macků, J. ; Kohout, M. ; Rožnovský, J.
For environmental risk estimation of Norway spruce ecosystems under climate change, the space means for each „forest vegetation degree“ in the frame of all so called „natural forest areas“ basic climatic characteristics (above all mean daily diameter, daily precipitation sum) and two climatic extremes (number of days with daily precipitation sum < 1 mm, number of days with maximum temperature > 30 oC) were computed. Aggregate typological units, as“forest type sets” and “management types” in combination with “forest stand types”, were used for environmental risk estimation at „natural forest areas“ and whole Czech Republic levels. Endangered forest stands, occurred in given “forest type set”, „forest vegetation degree“ and „natural forest area“ were estimated using comparison of basic and derived climatic parameters between all 5 time period (1961–2099). Measured data from climatic stations were used for the period A (1961–1990) and B (1991–2009); for periods C (2010–2039), D (2040–2069) and E (2070–2099) the data were modeled by climatic model ALADIN-Climate/CZ. This procedure enabled to distinguish all „natural forest areas“ into “warm” ones, which do not meet requirements for ecological conditions of Norway spruce at present period B and “cold” ones which meet them
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