Among the occurrences related to water cycle there are also extreme weather phenomena like drought and floods. Despite the fact the drought is a complex phenomena which causes a lot of economic and environmental damage, still is one of the less explored natural disasters. Therefore in the first part of this thesis we described features of drought, the reasons for its appearance and characteristics which distinguish it from other natural disasters. To quantify the various types of drought there are numerous drought indices in use. For the analysis of past drought events and trends in drought in Slovenia we selected Standardized Precipitation Index. The only input data for its calculation is based on monthly rainfall. The calculation requires determining the most appropriate theoretical distribution that best describes the precipitation data set. So we tried to find in thesis the influence of theoretical distributions on the values of SPI. With the most appropriate theoretical contribution we calculated SPI for selected meteorological stations at six different time scales (one-, two-, three-, six-, nine-and twelvemonth). For the period 1951-2004, we did again the calculation of indices for all selected stations and time scales. We found out that in most cases, the meteorological stations of Ljubljana-Bežigrad, Novo mesto and Trieste show a similar pattern of occurrence of drought and wet periods, which could be also said for the meteorological stations of Celje and Maribor-Tabor. In the last part of thesis we tried to identify the hydrological drought in the selected river basin of river Pesnica through a standardized monthly flow and SPI. The interrelation of standard flow and precipitation of Pesnica is positive for all time scales of SPI calculation. However the values of the correlation coefficient vary monthly and depends on the duration of time scale. The highest correlation is calculated between SPI-2 in September and standardized September flow.