Flood quantile estimation in ungauged basins is often performed using regional analysis. A regionalization procedure consists of two phases: the definition of homogeneous regions among gauged basins, i.e., clusters of stations, and information transfer to the ungauged sites. Due to its simplicity and widespread use, a combination of hierarchical clustering by Ward’s algorithm and the index-flood method is applied in this research. While hierarchical clustering is very efficient, its shortcomings are the lack of flexibility in the definition of clusters/regions and the inability to transfer objects/stations from one cluster center to another. To overcome this, using silhouette width for induced clustering of stations in flood studies is proposed in this paper. A regionalization procedure is conducted on 53 gauging stations under a continental climate in the West Balkans. In the induced clustering, a negative silhouette width is used as an indicator for the relocation of station(s) to another cluster. The estimates of mean annual flood and 100-year flood quantiles assessed by the original and induced clustering are compared. A jackknife procedure is applied for mean annual flood estimation and 100-year flood quantiles. Both the Hosking–Wallis and Anderson–Darling bootstrap tests provide better results regarding the homogeneity of the defined regions for the induced clustering compared to the original one. The goodness-of-fit measures indicate improved clustering results by the proposed intervention, reflecting flood quantile estimation at the stations with significant overestimation by the original clustering.

Changes in the hydrological regime are widely investigated using a variety of approaches. In this study, we assess changes in annual and seasonal flow characteristics based on a probabilistic representation of the seasonal runoff regime at the daily time scale. The probabilistic seasonal runoff pattern is constructed by determining quantiles from marginal distributions of daily flows for each day within the year. By applying Fourier transformation on the statistics of the daily flow partial series, we obtain smooth periodical functions of distribution parameters over the year and consequently of the quantiles. The main findings are based on the comparison of the dry, average, and wet hydrologic condition zones as defined by the daily flow quantiles of selected probabilities. This analysis was conducted for ten catchments in Serbia by considering changes between two 30-year nonoverlapping periods, 1961–1990 and 1991–2020. It was found that the relative change in runoff volume is the most pronounced in the extreme dry condition zone in the winter season (−33% to 34%). The annual time shift is the largest in the dry and average condition zones, ranging from −11 to 12 days. The applied methodology is not only applicable to the detection of hydrologic change, but could also be used in operational hydrology and extreme flow studies via drought indices such as the Standardized Streamflow Index.

Regional analysis is often used for flood quantile estimation in ungauged catchments. The regionalization procedure has two phases: the formation of homogeneous regions and flood quantile estimation. The presented research results consider the first phase of the regional analysis for 41 catchments in Serbia. The catchment similarity attributes are catchment area and catchment mean elevation. The number of formed regions and the number of stations within the regions are determined by maximising the mean silhouette width of the region. Regions were first obtained by cluster analysis and then adjusted to comprise catchments with a positive silhouette width. For the three formed regions, homogeneity was checked by the Gini index - GI.

An analysis of mean annual runoff was conducted for a small ungauged catchment of the Tulovska River in the South Morava River Basin. Langbein?s method, Turk?s method and regional regression models were applied for obtaining the mean runoff. Long-term mean temperature, annual precipitation and the mean catchment elevation are used as input data. The estimations were conducted using various sources of climatological input data and the results were then compared. Precipitation and temperature data were derived, in a 10 km x 10 km resolution raster data format, from the digital data repository of the CarpatClim project. Point measurements of temperature and precipitation by the Republic Hydrometeorological Service of Serbia were also used as input data and compared with the raster data. The difference between the raster and point meteorological data were attributed to the effects of terrain elevation spatial variability, not captured in the raster data. The analyses showed that the predicted mean runoff can differ up to 50%, depending on the chosen method and the input data.

Nestašice vode tokom leta 2024. i 2025. godine skrenule su pažnju javnosti na hidrološke suše. U ovom radu se analiziraju promene količina raspoloživih površinskih voda i učestalosti pojave ekstremno malih protoka na do­micilnim rekama Srbije u periodu 1950-2024, na osnovu podataka sa 12 hidroloških stanica. Razmatrani nizovi godišnjih protoka, srednjih protoka u malovodnoj sezoni, kao i minimalnih srednjih mesečnih i višemesečnih pro­toka imaju izražene višegodišnje cikluse koji se posled­njih 10-15 godina manifestuju kao opadajući trend. Re­zultati analize homogenosti nizova pokazali su značajno smanjenje godišnjih količina voda u profilima 6 stanica u istočnoj i južnoj Srbiji, dok su promene u malovodnom periodu i u nizovima minimuma statistički značajne samo u slivu Crnog Timoka i delimično u slivu Toplice. Sma­njenje protoka se može načelno povezati sa osmotrenim smanjenjem letnjih padavina. Sa ovakvim analizama rad želi da podstakne dalja istraživanja hidroloških suša u Srbiji imajući u vidu rastući rizik od njihove pojave i zna­čajan uticaj na vodosnabdevanje. U tom smislu, analize hidroloških suša treba da uključe ne samo raspoložive površinske već i podzemne vode kako bi se obezbedio sveobuhvatni pristup upravljanju vodnim resursima i raz­voj nacionalnih strategija za adaptaciju na klimatske pro­mene.