Vol. 109, No. 1 * Pages 1–69 * January - March 2005

Precipitation is one of the most important elements of the hydrological cycle, and extreme events associated with precipitation are considered a key factor in several types of human activities, including agriculture, for instance. Therefore, the main objective of this paper is to evaluate extreme precipitation indices. Several climate extreme indices have been analyzed and compared for the entire world, the European continent, and the Carpathian Basin for the second half of the twentieth century according to the guidelines suggested by the joint WMO-CCl/CLIVAR Working Group (formed at the end of the 1990s) on climate change detection. These extreme precipitation indices include the number of wet days using several threshold values, e.g., 20 mm (RR20), 10 mm (RR10), 5 mm (RR5), 1 mm (RR1), 0.1 mm (RR0.1), the upper quartile and the 95th percentile of daily precipitation in the baseperiod 1961–1990 (R75 and R95); the maximum number of consecutive dry days (CDD); the highest 1-day precipitation amount (Rx1); the greatest 5-day rainfall total (Rx5); the annual fraction due to extreme precipitation events (R95T); simple daily intensity index (SDII); etc. Our results suggest that regional intensity and frequency of extreme precipitation increased in the Carpathian Basin during the second half of the twentieth century, while the total precipitation decreased, and the mean climate became slightly drier.

Various components in the microclimate of irrigated and rainfed maize stands were examined in Keszthely, Hungary, from the end of June 2001 until the first ten days of August. To simulate the elements of microclimate, Crop Microclimate Simulation Model of Goudriaan (1977) was applied. The air temperature and humidity were registered using a Temperature/Relative Humidity Sensor, attached to a data recorder placed in a Stevenson screen, close to the tassel level of the adult plants (1.40 m above the soil surface). Measured and simulated values were compared with respect to hourly means of samples taken every 4 seconds, and diurnal means calculated for the daylight hours. The weather on certain sampling days (rain and strong winds) resulted in a microclimate simulation so far from reality, that these days were omitted from the evaluation. The difference between the diurnal means of simulated sampling days and the measured values was small, less than 1 °C for the air temperature, and below 10% for the relative humidity. The simulation of air temperature was closer to the field parameters in the non-irrigated treatment. The difference between the observed and simulated air moisture values was much the same in the two water supply treatments. The microclimate simulated was such a good approximation to reality that the simulation was able to reflect events causing very slight differences, such as the effect of irrigation. This indicates that a knowledge of the changes in the microclimate, expected as the result of various agronomic measures, could form the basis for better decisions by farmers.

Multi-layer microclimate simulation models describe the profiles of meteorological variables inside the canopy. For a steady state model, the instantaneous values of air temperature, vapor pressure, wind speed, and global radiation are needed as input variables from a given height above the canopy. A standard automatic meteorological station provides all those data with high frequency in time, but from outside of the canopy. A simple calculation method is presented in this paper for evaluation „above canopy” data from standard data. Roughness parameters are considered in three different ways. Applying the methods for an experimental maize field, measured plant characteristics were used. At the beginning of the vegetation season and in the senescence period, the differences in roughness parameters due to different approaches were negligible, the largest difference in roughess parameters occured at the fully developed plant stand. The differences occurred due to application of the calculated different roughness parameters in profiles of meteorological elements were small even at this time. We concluded that data transferring is needed because of keeping consistency among meteorological data, at least plant height must be taken into account in determination of surface roughness length and zero-plane displacement. Further plant characteristics as LAI, the width of the leaves, and the drag coefficient of the leaves can also be taken into account, for it makes the method more general, but in the case of maize stand, the effect on the profiles of meteorological elements is rather small.

Global climate changes affect the atmospheric circulation over the European synoptic region and, in particular, over the Mediterranean. In recent years the activity of cyclogenesis has strongly diminished over the Western Mediterranean and is not typical for the eastern part of the region. The present work is a climatological investigation of synoptic scale Mediterranean cyclones in relation to the number of cyclones originating over the Mediterranean, their paths of movement, and the interannual activity of the Mediterranean center. A study was carried out using surface pressure charts from the Synoptic Archive of the National Institute of Meteorology and Hydrology of Bulgaria for the period 1980–2001. The comparison of the derived results with the results of other authors obtained for previous periods show a well pronounced decrease in the number of Mediterranean cyclones. At the same time, the activity of the Mediterranean center during the course of a year is about two months shorter. After 1990, considerable changes in the regular paths of Mediterranean cyclones were observed.