Estimation of biologically effective UV radiation in Croatia

Sa？etak Background and Purpose: Solar UV radiation is harmful to plants: it reduces photosynthesis, stunts growth, and causes a variety of damage to a plant. The purpose of this study was to estimate solar UV exposure and harmful biologically effective irradiance during the vegetative growth period in Croatia. Biologically effective irradiances were calculated for several action spectra. Data were analyzed in order to establish the relationship between UV exposure, time of a day and week of the year. Simplified formulas were developed that mimic complex radiative transfer models. Methods: UV radiation in Croatia was estimated using the Tropospheric Ultraviolet-Visible (TUV) model, version 4.2. Dose rates harmful to plants (UV-B, UV-A) and also useful photosynthetically active radiation dose rate (PAR) were calculated at 13 h (CEST) at fifty sites during the vegetative growth period (April-October). Daily and monthly variations of UV-B dose rate (irradiance) were calculated (and some approximate formulas were developed) for one representative location. Biologically effective UV daily doses were calculated using data on four different action spectra. Results: In July, at some elevated locations, UV-B irradiance was higher than 2 Wm–2 at 13 h (CEST). The biologically effective UV daily doses ranged from 29 kJ m–2 in October to 72 kJ m–2 in July. The daily doses calculated in this study are the maximum values; all calculations refer to clear-sky conditions and to the total ozone column value 300 DU, which approximately corresponds to the lowest total ozone value measured during the vegetative growth period. Conclusions: UV exposure in Croatia was estimated at one location chosen as representative. Simplified formulas that describe daily and monthly variations of UV-B irradiance may be used instead of the TUV model and produce a relative error of less than 10 %. Corrections for the total ozone column and cloudiness are also possible