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.
This study evaluates occurrence of the heavy rains at urban areas on the example of Brno agglomeration. Extreme precipitation events are studied with the help of 1-minute records from three urban sites in the Brno and one site in the rural region. Additionally data from nine Hellmann rain gauges from Brno and surroundings were used. The event of torrential rains was evaluated according to Wussow's method. The study found that torrential rains occurred in Brno in the season from April to November. The fifteen-year long observation of the phenomenon at Brno-Žabovřesky station shows varying frequency of torrential rainfall -from none in 2007 to four in 2004 and 2010. The most extremal was catastrophic downpour on July 15, 2009 when precipitation sum reached total up to 42.7 mm in 52 minutes and the maximal rainfall intensity was 4.1 mm/min. This phenomenon occurs only one day after downpour on July 14, 2009. The overall number of torrential episodes is not very high, but it is compensated by the fact that they can repeat in a relatively short period of time, due to specific synoptic conditions. Maximum rainfall intensity during torrential rains reaches values of about 3 mm / min and the average proportion of torrential rain in the daily precipitation sum is around 70%. The phenomenon of heavy rains represents a significant problem for densely populated urban areas because such extreme rainfall has a large impact on the hydrological system of cities.
The agrometeorological model named AVISO is developed and operated at the Czech Hydrometeorological Institute as a tool for calculation the evapotranspiration and soil profile water content. The model uses modified evapotranspiration equation developed by Penman and Monteith. The basic calculated surfaces are water level, bare soil, grass and a few field crops. As part of the research project, some AVISO model procedures and canopy parameters were modified for usage in fruit orchard. Data and observation from apple, cherry and apricot orchards from 2020 to 2022 were used to set up the model and to validate the model results. By determining the hydrolimits of the soil and the characteristics of the root zone of the trees, the water capacity of the model soil profile was estimated. The AVISO model results were compared with measured soil moisture, which was converted to the average soil profile saturation determined in percentage of available water capacity. When tuning the model, emphasis was placed on the decreasing part of the soil water content curve interpreting the intensity of evapotranspiration. In many iterations of the calculation, the results of the model were compared with the measurements using the correlation coefficient, the average bias and the mean absolute error. The average model-measurement correlation values for months in the growing season (April–September) in 2020 and 2021 were between 0.30 and 0.99. The bias error values were between -13.14 and +38.31 mm. The second comparison option was to use the precipitation sums for time periods determined by the almost identical moisture at the beginning and the end of the period. The amount of precipitation in the given section thus theoretically coincided with the sum of evapotranspiration. Correlations of model evapotranspiration and evapotranspiration calculated on the basis of this simple precipitation balance reached values of up to 0.9 for some variants of orchards. Despite some weaknesses, the model results are satisfactory in some experimental stands, especially in apple orchards. The modified model was used to calculate the long term average water balance of apple trees within the territory of the Czech Republic for the growing season for the period 1991-2020. Composition of seven maps was produced - six maps for monthly data and one for entire growing season. The values of water balance for summer months are in range from -77 to +125 mm, sum for growing season is in range from -323 to +563 mm. The lowest values indicating the threat of drought are in the South Moravia region. Among other things, improved model and maps can help to optimize water management and irrigation in orchards.
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 (1 st May to 30 th 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.KEY WORDS: urban climate, amount of evaporation, EWM, water balance ARTICLE HISTORY:
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