Investigation of Spatial and Temporal Variability of Hydrological Drought in Slovenia Using the Standardised Streamflow Index (SSI)

Drought is a complex phenomenon with high spatial and temporal variability. Water scarcity has become a growing problem in Slovenia in recent decades. Therefore, the spatial and temporal variability of hydrological drought was investigated in this study by analysing the Standardized Streamflow Index (SSI). Monthly discharge data series from 46 gauging stations for the period 1961–2016 were used to calculate SSI values at five different time scales (1, 3, 6, 12, and 24 months). The results indicate that the frequency and intensity of droughts in Slovenia has increased in recent decades at most of the analysed gauging stations and at all time scales considered. Spring and summer periods were identified as critical in terms of water deficit. SSI values vary independently from the location of the gauging station, confirming that drought is a regional phenomenon, even in a small country such as Slovenia. However, SSI values vary considerably depending on the time scale chosen. This was also confirmed by the results of the hierarchical clustering of the number of extreme droughts, as various time scales resulted in a different distribution of gauging stations by individual groups.

Analysis of droughts due to the operation of water structures: Gidra river case study

The paper deals with an analysis of a drought in the small basin of the Gidra River in Slovakia due to problems with the abstraction of water from small reservoirs and ponds. A detailed hydrological assessment of the M-daily discharges for a long-term period was based on a dataset from the only gauging station on the upper part of the river. Because of the existing water structures with prescribed operations during the year, hydrometric and geodetic measurements were taken by the authors. The solution to this problem represents the conditions for the minimum required Q355 discharge in the river anytime and anywhere. This can only be solved with a master operational manual for the whole river to be able to flexibly react to the current hydrological situation.

Data- and Model-Based Discharge Hindcasting over a Subtropical River Basin

This study aims to evaluate the performance of the Soil and Water Assessment Tool (SWAT), a simple Auto-Regressive with eXogenous input (ARX) model, and a gene expression programming (GEP)-based model in one-day-ahead discharge prediction for the upper Kentucky River Basin. Calibration of the models were carried out for the period of 2002–2005 using daily flow at a stream gauging station unaffected by the flow regulation. Validation of the calibrated models were executed for the period of 2008–2010 at the same gauging station along with another station 88 km downstream. GEP provided the best calibration (coefficient of determination (R) value 0.94 and Nash-Sutcliffe Efficiency (NSE) value of 0.88) and validation (R values of 0.93 and 0.93, NSE values of 0.87 and 0.87, respectively) results at the two gauging stations. While SWAT performed reasonably well in calibration (R value 0.85 and NSE value 0.72), its performance somewhat degraded in validation (R values of 0.85 and 0.82, NSE values of 0.65 and 0.65, for the two stations). ARX performed very well in calibration (R value 0.92, NSE value 0.82) and reasonably well in validation (R values of 0.88 and 0.92, NSE values of 0.76 and 0.85) at the two stations. Research results suggest that sophisticated hydrological models could be outperformed by simple data-driven models and GEP has the advantage to generate functional relationships that allows investigation of the complex nonlinear interrelationships among the input variables.

Assessing the impact of climate on annual and seasonal discharges at the Sremska Mitrovica station on the Sava River, Serbia

Flood frequency analysis was performed on annual maxima series for 90 years (1928–2017) of discharge data recorded at the Sremska Mitrovica gauging station on the Sava River. The three-parameter distributions (PearsonIII, Log-PearsonIII) are more suitable for modelling annual maxima than distribution functions with only two parameters (Normal, Log-normal, Gumbel). The Mann–Kendall test statistic indicated that there is no statistically significant trend identified in annual maximum discharges or average annual discharges. A positive increasing trend was observed in annual temperature, while annual precipitation shows a decreasing trend which is non-significant. The seasonality analysis found a statistically non-significant weak negative trend in discharge in spring, summer and autumn and a statistically non-significant weak positive trend in winter. During winter, spring, and summer a non-significant negative trend in precipitation was observed, while autumn has experienced a statistically significant increasing trend. Temperatures show a positive trend in all seasons, but only temperatures during the warm period show a statistically significant increase. The results demonstrate that decreasing discharges of the Sava River at the Sremska Mitrovica gauging station are mainly the consequence of decreasing precipitation and increasing temperature (increasing evaporation), which is consistent with the results of other studies of the region.

Mathematical models of water surface for geodetic support of construction in agro-industrial complex

The purpose of the study was to analyze the possibilities of using mathematical models of the water (level) surface of rivers and reservoirs for the transfer of elevations. The use of an empirical mathematical model obtained for the Irtysh River near the city of Omsk makes it possible to determine the heights in the investigated area with an accuracy of about 0.1 m. To determine the level of the water edge at the selected area, it is necessary to obtain: the mark of the water edge at the gauging station; the distance along the river from the gauging station to the work site. It is advisable to fix the water level at the gauging station and the work site simultaneously. For the elevation transfer from one river bank to another by the III class leveling program, the authors propose the technology of laying temporary benchmarks on the banks, fixing the level using special devices, and transferring the elevations of the fixed water level to temporary benchmarks. The technology contains the devices of simple design for accurate level fixing. The factors influencing the accuracy of the height transmission are: fixing the water level, the centrifugal forces of the flow, the Coreolis force caused by the rotation of the Earth, and the wind surge. The authors calculated the expected values of errors determining the accuracy: for fixing the level it was about 1 mm according to the proposed method; the height difference at the banks due to the forces of Coreolis was 0.007 m; the influence of centrifugal forces at a turning radius of 500 m causes a difference in heights at opposite banks of 0.1 m. In the result, the authors proposed the recommendations developed for transferring heights from one river bank to another using a class III leveling program, which ensure the specified accuracy.

Water Regime and Flow Trends of Sitnica River

River Sitnica is one of the large rivers of Kosovo, which makes problems through its river basin, such as frequent floods and pollution. Especially if we add impact of climate change, then problems get worse. Among all, there is a lack of continuous hydrometrical observation. Those existing data are not complete, and not so confident. So, before any estimation of water regime, flow trends and identification of climate change, there is first to analyze flow data, to complete them with the known statistical methods. In this case, this problem has been solved by method of correlation with neighbourhood well-observed data. Just after data validation, there has been analyzed and shown its water regime, estimated flow trend, and is given correlation of temperatures, precipitations and flows for main gauging station. Correlation of these basic parameters has been extended for 21 years, where can be seen strong increasement of precipitation, certain increasement of temperatures and flows, as well as strong extremization of these parameters. At the end is given impact of convection rainfall, due to intensiv urbanization. These results should alarm competent authorities, on preventive action, to soft consequences, in next two decades.

Investigation of Basin Characteristics: Implications for Sub-basins Level Flood Peak and Vulnerability Assessment

Flood vulnerability is a significant component in assessing the probable degree of damage to various exposures in hazard conditions. In this study, a semi-distributed event-based hydrological model and indicator-based method were applied to evaluate the sub-basin level flood vulnerability using the Geographical Information System (GIS). The flood peak discharge of each sub-basin corresponding to the 2014 extreme flood of the Jhelum river was related with different sub-basins characteristics (terrain, hydrological, land use and soil) using a theoretical framework under an indicator-based method. The calibrated (2014) and validated (1992, 1997) hydrological model showed Nash-Sutcliffe Efficiency (NSE) of 0.98 and (0.99, 0.99) at relatively upstream gauging station Sangam against optimized Curve Number (CN) scaling factor of 0.98. The Anantnag and Kulgam districts, exhibiting multiple sub-basins contributing to the Sangam gauging station, are falling into a highly vulnerable category located in the Jhelum basin's southern part, Greater Himalayan Range. It was also revealed that sub-basins at the upstream of the Jhelum basin are more vulnerable compared to downstream area, where sub-basin W810 (Greater Himalayan), Anantnag district draining at Sangam gauging site is found as most vulnerable among the all other sub-basins. However, hydrological characteristics control the most vulnerable sub-basin peak discharge rather than other characteristics such as terrain, soil, or Land Use. Outcomes of the study will be helpful in prioritizing the flood mitigation planning not only with respect to the hydrological boundary (sub-basin level) but also with administrative district boundaries. The proposed method is generic and can be applied to any flood-prone river basin.