No abstract

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.

During dry periods, the flow of medium and small streams is significantly reduced and equal to groundwater flow. Since the base flows provide information about aquifer characteristics and retention characteristics of a basin, the possibilities of analysis and simulation of base flows gain importance under the conditions of intensive water use and the increasing demand for adequate water quality protection. In this paper, a model was established and used for the description of the principles governing the changes of base runoff on the basis of a streamflow hydrograph registered at the outlet of the basin on the example of the Kolubara basin up to the „Valjevo” profile. Since the amount of base runoff from a basin cannot be measured, the results of base flows obtained using the local minimum method were adopted as the criterion for the comparison of the modelled values of base runoffs. The created model was applied for making simulations of the base runoff hydrograph during three characteristic years (rainy 1970, average 1985, and dry 1990). Deviations between the base flow values obtained using the established model and by applying the local minimum method are acceptable from the standpoint of general hydrological accuracy

During the drought the flow in streams is reduced and is dominated by base flow. Baseflows are characteristic of low flow periods and provide information on available water resources in the basin during the drought, particularly on the aquifer and retention basin characteristics. This paper deals with the possibility of analysis and simulation of baseflow, and the determination of the pattern of its changes based on the total registered streamflow hydrograph at the catchment outlet. The basis for modeling the base flow changes in the time were base flow values obtained from the streamflow hydrograph by application of the graphical local minimum method. Applying the simulation model developed in this study, simulations of base flow hydrographs were performed for three characteristic years (1970, 1985, and 1990). It was shown that discrepancies between values of the base flows obtained through application of the local minimum method and the model are within the limits of tolerance. [Projekat Ministarstva nauke Republike Srbije, br. 37003

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.