Drought is a complex natural hazard, connected with water availability, that affects different ecosystems. Because of its complexity it is hard to define, qualify and monitor. In this master thesis, special attention was given to the hydrological drought, which is less investigated compared to the meteorological drought. In the first part of the master thesis, we did the overview of different indicators (indices) with which we can define hydrological drought.
For study of hydrological drought on surface waters in Slovenia, we used standardized streamflow index (SSI) and streamflow drought index (SDI). We calculated both drought indices on different time scales so it is easier to define the beginning, duration and intensity of hydrological drought. The only input data for the calculation of both indices are time series data of discharges. Because the basic method of calculation of both indices is analogic to the method of calculation of standardized precipitation index (SPI), we used SPI and DrinC software to calculate indices for chosen hydrological stations.
In the final part of the thesis, we analysed results of calculated indices and made comparison of SDI index calculated with two different distributions, namely gama and log normal distribution. Comparison of SSI and SDI indices showed that both methods gave equal results, so further analyses, were made only for SSI index. We discovered that the variability of SSI is higher on longer time scales than on shorter ones. We presented spatial distribution of indices for a typically wet (1965) and a dry year (2003) for chosen hydrological stations in Slovenia. Furthermore, we analysed index results for a dry year of 2003 with Orange software, using heatmaps. For chosen hydrological stations, we defined the number of severe and extreme droughts. We sorted the hydrological stations into groups by similarity of drought events using hierarchical clustering method. We discovered that drought doesn’t affect all regions in Slovenia evenly, but is rather a regional phenomen.