Effect of water on bimodality of air temperature distribution functions and changes in T-year air temperature values in Hurbanovo

Variability and long-term trends in air temperature are in the interest of hydrologists in recent decades as they can affect the global hydrological cycle and water balance in river basins. The estimation of the T-year minimum and maximum mean daily air temperature is associated with the problem of selection of the distribution functions of these series. The histograms of the daily air temperature series manifest the two-peak (bimodal) shape in many stations all over the world. It is not feasible to describe the distribution function of bimodal distribution through single mean value and single standard deviation. In the present study the T-year values of air temperature are estimated for three temperature indexes in station Hurbanovo: 1. series of maximum mean daily air temperature of the year Td,max, 2. series of mean annual air temperature of the year Td; and 3. series of minimum mean daily air temperature of the year Td,min. Change in the theoretic distribution curve of the mean daily air temperature indexes is compared during two subperiods of the instrumental period 1872–2017. Generally, the changes in temperature design values are more marked in case of minimum temperatures, e.g. the value of 100-year minimum mean daily air temperature increased by more than 5°C. The 100-year maximum mean daily air temperature increased by 1.88°C in Hurbanovo.