Snow cover occurrence affects wintering and lives of organisms because it has a significant effect on soil frost penetration. An analysis of the dependence of soil frost penetration and snow depth between November and March was performed using data from 12 automated climatological stations located in Southern Moravia, with a minimum period of measurement of 5 years since 2001, which belong to the Czech Hydrometeorological institute. The soil temperatures at 5 cm depth fluctuate much less in the presence of snow cover. In contrast, the effect of snow cover on the air temperature at 2 m height is only very small. During clear sky conditions and no snow cover, soil can warm up substantially and the soil temperature range can be even higher than the range of air temperature at 2 m height. The actual height of snow is also important – increased snow depth means lower soil temperature range. However, even just 1 cm snow depth substantially lowers the soil temperature range and it can therefore be clearly seen that snow acts as an insulator and has a major effect on soil frost penetration and soil temperature range.
Mojmír Kohu, Jaroslav Rožnovský and Grazyna Knozová
Information about water evaporation is essential for the calculation of water balance. Evaporation, however, is a very complex physical process and it is therefore difficult to quantify. Evaporation measurements from the weather station network of the Czech Hydrometeorological Institute between 1968 and 2011 were performed using the evaporimeter GGI-3000. Evaporation was calculated using modified standard method based on FAO. The aim of the article was to compare the measured values and calculations. It has been found that the evaporation values from water surface calculated using the empirical equation are usually higher than the measured values by on average 0.8 mm, in extreme cases even 6.9 mm. The measured data shows higher variability than the calculated values, which means that correlations between series are not strong, the correlation coefficient being 0.7. Nevertheless the findings can be used for homogenization of series measured by the GGI-3000 evaporimeter.
Hana Stŕedová, Tomáš Stŕeda and Jaroslav Rožnovský
Official price of farmland in the Czech Republic is based on land value in different soil and climatic conditions. The paper compares relevant climatic and agroclimatic characteristics used for land appraisement. Characteristics defined in climatic region of estimated pedological ecological unit system for two fifty years period 1901-1950 and 1961-2010 were evaluated. Area of interest includes 53 points distributed within nine broad areas of the Czech Republic. It is evident that the development of climate has an enormous impact on soil fertility. Difference of station average values of air temperature of both fifty years vary from −0.5 to 1.1 ◦ C (mean difference is 0.3 ◦ C) in the case of vegetation period. The shift of precipitation is not so evident as in the case of temperature. The long term change in precipitation distribution within a year is documented by a different shift of annual, vegetation period and non-vegetation period values. Moisture certainty in vegetation period decreases in all cases of broad areas (except one region). All 50year averages of investigated parameters had been changed in 1961-2010 compared to the mean of 1901-1950. This should be taken into account when fixing the official price. Climatic region parameters should be replaced by a more complex “agroclimatological characteristic”, which take into account also the basic pedological and plant characteristics, for example the available water holding capacity.
Hana Stredová, Jaroslav Rožnovský and Tomáš Streda
Predisposition of drought occurrence is based on combined evaluation of above-normal temperatures and below-normal precipitation. According to the weight of the individual categories of extremity, the five degrees of predisposition to drought were determined (degree 1 is the lowest risk, degree 5 is the highest risk). Evaluation of temperature extremity is based on the determination of abnormality in comparison with average value and standard deviation. Individual categories of extremity of precipitation are determined by comparing the individual monthly data with percentile values. Monthly data of homogenized technical series of the Czech Hydrometeorological Institute were evaluated for the years 1961-2010 in two climatologically dry areas (Breclav and Kladno county in the Czech Republic). Fourty-two months were rated risky in Breclav county and fourty-four in Kladno county. The evaluation shows an increase of predisposition to drought, especially after 1990. The highest incidence of degree 5 was recorded in 2001 to 2010 in vegetation season. Subsequently the drought variability as a mean variance of years/season and drought severity as a sum of degree of predisposition to drought of years/season were assessed. A gradual increase of variability and severity from 1961-1970 to 2001-2010 is visible. The lowest values of variability (maximum 2) and severity (maximum 3) in both counties were recorded in winter.
Mojmír Kohut, Jaroslav Rožnovský, Gražyna Knozová and Jáchym Brzezina
Evaporation from water surface at the station in Ústí nad Orlicí was measured using an automatic EWM evaporimeter. The analysed period was from May 1st to September 30th in the years 2001 to 2014. Statistical analysis of the daily evaporation showed that the values ranged between 0.0 mm and 7.3 mm (July 17, 2007). This maximum value was analysed in detail and considered to be realistic based on the unusual weather conditions on that day. The highest average daily evaporation was observed in July (2.8 mm), followed by August (2.5 mm). On the other hand the lowest average daily evaporation was found to be in September (1.6 mm). Average monthly evaporation totals in the analysed period (2001–2014) ranged from 49.1 mm (September) to 86.1 mm (July). The absolute lowest monthly evaporation total in the analysed period was measured in September 2002 (34.4 mm), on the other end of the scale, the absolute highest monthly evaporation in the period of interest was measured in August 2003 (114.5 mm). Statistics of annual data show that out of the 14 years analysed, the lowest evaporation was observed in 2005 (263.5 mm), while the highest in 2007 (426.1 mm). Average annual (May-September) evaporation for the 14 years is 355.0 mm. The trend in evaporation for May and August is negative, in the other months it is positive. The largest change was seen in July, where the linear index value is +1.555. However, the trends in monthly values are not statistically significant.
Jaroslav Rožnovský, Tomáš Litschmann, Hana Středová, Tomáš Středa, Petr Salaš and Marie Horká
Urban environment differs from the surrounding landscape in terms of the values of meteorological parameters. This is often referred to as the urban heat island (UHI), which in simple terms means higher air temperatures in cities. The cause of these changes lies in the different active surfaces in cities, which subsequently results in a different radiation balance. The higher temperatures, however, also affect the living conditions in the city and during very high temperature periods can have negative effects on the health of the city inhabitants. The results presented in this paper are based on measurements taken over several years at locations near Hradec Králové, which is surrounded by different surface areas. Environment analysis was performed using the Humidex index. The obtained results show that replacing green areas with built-up areas affects temperatures in the city, when air temperatures are very high they significantly increase the discomfort of the inhabitants. Differences in the frequency of discomfort levels are observed especially during periods of high temperatures, at lower temperatures these differences are not significant. Higher frequencies of discomfort are observed at locations with artificial surfaces (asphalt, cobblestones, concrete) and in closed spaces. In contrast, locations with lots of green areas almost always have the value of this index lower or more balanced. The results should therefore be a valid argument for maintaining and extending green areas in cities.
Gražyna Knozová, Jáchym Brzezina, Jaroslav Rožnovský and Mojmír Kohut
The subject of this study is an evaluation of the amount of evaporation from water surfaces (VVH), measured using EWM devices in two cities of different sizes, and located approximately 80 km from each other – Prague and Pilsen. The results were analyzed in the context of urban phenomena, which are pronounced especially in Prague, and also in the context of meteorological and morphological conditions in those locations. It was found that higher amounts of evaporation were measured at the meteorological station in Pilsen. The difference between the average sum of VVH per season (1st May to 30th September) between 2005 and 2014 for the two locations is 33.3 mm. The difference between daily average values was 0.2 mm. Given the suburban nature of the two locations where measurements were taken, it was not possible to draw any conclusions about the effect of the urban heat island on the rate of evaporation and values of VVH. Factors significantly influencing VVH are surface roughness, which is higher in urban environments than in open landscapes. Based on the results it was concluded that at both a regional and a local scale, the rate of evaporation is more affected by wind speed than thermal conditions. The measured VVH values differ, not just because of the urban dimension of the two cities compared, but especially as a result of different topoclimatic location of the two stations.
Tomáš Středa, Hana Středová, Filip Chuchma, Josef Kučera and Jaroslav Rožnovský
The occurrence of drought during flowering (usually from the end of May to the beginning of June) is the most hazardous timing in terms of the possible negative impact of agricultural drought on winter wheat, which is the most cultivated crop in the Czech Republic (about 800000 ha). Lack of water, often accompanied by high temperatures, negatively affects the number of grains in the wheat ear and the tissue development of the developing grain, with consequent impacts on yield and quality of product. With the use of a) long-term time series of agrometeorological data (1961–2010), b) long-term phenological time series of winter wheat (1981–2010), and c) soil conditions data (available water capacity of soils of the Czech Republic) for the arable soil, the ratio of actual evapotranspiration and potential evapotranspiration for the period of 1961–2010, used as an indicator of agricultural drought (lack of water) for wheat, was calculated. The innovative aspect of this categorization of the territory of the Czech Republic according to the risk of occurrence of agricultural drought for winter wheat is considering drought from the aspect of the plant, i.e., evaluation based on the actual consumption of water by the vegetation. This is a very sophisticated procedure. Frequently, water content in soils data, presented as an output of some models, do not fully indicate the possible negative impacts on yield generation because the plants themselves are typically not considered. The method used in this study is universally applicable and allows comparisons of regions at the local, regional, and supra-regional levels. For estimation of the development of agronomic drought in the future, the basic water balances in the growing seasons of 1961–2010 and 2071–2100 were compared using a climate scenario. The forecast indicates a significant deterioration of agricultural drought in the region with probable direct impacts on agricultural production.
Tomáš Litschmann, Jaroslav Rožnovský, Tomáš Středa, Hana Středová and Jiří Hebelka
The paper deals with the evaluation of temperature and humidity measurements in the vertical profile of Macocha Abyss (Moravian Karst, South Moravia, Czech Republic). The measuring profile on a rock wall is made up of seven HOBO-PRO sensors. Two other meteorological stations are installed at the bottom and near the upper edge of the abyss. The evaluation was designed separately for warm season (June 1, 2008 to August 31, 2008) and cold season (November 1, 2008 to February 28, 2009). In the warm season, distribution of inverse temperatures dominated in the abyss. Temperature differences between the bottom of the abyss and its upper edge reached about 10 ◦ C. At the bottom of the abyss, the minimum temperatures proved to be higher than at its upper edge and in its vicinity. Thermal circulation is evident to the depth of about 60 m. The highest temperatures were observed in the deeper layers of the abyss in the warm period at around 10 a.m. of Central European Summer Time. Towards the upper edge of the abyss, the hour of daily maximum temperature shifts to 2 to 4 p.m. In the cold season, the minimum temperature was observed between 6 and 7 a.m. of Central European Time. A decrease in the accumulation of cold air (cold-air pool formation) was not found in the lower floors of the abyss. This phenomenon does not occur even during clear nights. The depth of 60 m from the upper edge of the area maintains a high relative humidity (above 95%) in the warm season. However, humidity decreases from this depth towards the top of the abyss. In the cold season, the whole abyss is filled with air with relative humidity of 90 to 95%.
Hana Středová, Jana Podhrázská, Tomáš Litschmann, Tomáš Středa and Jaroslav Rožnovský
The paper summarizes the results of wind velocity measurement in different distances from windbreak in combination with optical porosity (OP) determination in different periods. Experimental data were obtained by direct measurement of wind speed and OP analyses of images of four windbreaks in Southern Moravia (part of Czech Republic). Wind speed at 2 m above the soil surface in a defined distance from windbreak had been measured since 2006. Thirty images of different phenological stages of selected windbreaks from 2006 to 2010 were analyzed. Windward or leeward images were converted into black and white spectrum. All available measurements were used for a map creation. The highest values of OP (up to 50%) are achieved in non-vegetation period. Due to the high OP variability in height of terminal tree branches “OP reduced” was also assessed (just squares to 2/3 height of windbreaks were evaluated). The wind speed reduction on the leeward side relatively strongly correlated with OP value. The highest correlation was found out when the wind speed measurement at 50 m on leeward side was used. The dependence decreases with increasing distance. Full foliage in summer (10% OP) reduces a wind speed about 60% at 50 m and about 30% at 150 m on the leeward. These values for non-foliaged windbreaks decrease to 80 and 90%. Maximum distance of windbreak effect on wind speed reduction was found out by the extrapolation of the curves constructed using the regression equation of wind speed reduction in dependence on OP and different distances from the windbreak. Regardless of OP value, the reduction effect disappears at a distance of 250 m. The quietest zone of evaluated windbreak with an average height of windbreaks 15-18 m was detected in the area about four times the height (4H). The effect of windbreaks decreases with increasing porosity.