Acta Scientiarum Polonorum
serie Formatio Circumiectus – Environmental Processes
RESEARCH PAPER
Impact of drought on the flow regime in the Orljava River
1
Faculty of Civil Engineering and Architecture Osijek
These authors had equal contribution to this work
Submission date: 2026-02-04
Final revision date: 2026-04-01
Acceptance date: 2026-04-09
Online publication date: 2026-09-17
Publication date: 2026-09-17
HIGHLIGHTS
- Drought conditions were assessed using the SPEI
- An increased frequency of negative SPEI values was observed in the recent period
- In the recent period, also daily discharges in the Orljava River are reduced
- Recently developed NDI index was also used to confirm results of SPEI
KEYWORDS
DroughtStandardized Precipitation Evapotranspiration Index (SPEI)Požegathe Orljava RiverThe New Drought Index (NDI)
TOPICS
ABSTRACT
Aim of the study:
The aim of the study is to analyze the occurrence of drought in Požega, its temporal evolution, and its influence on daily discharges of the Orljava River, which flows through Požega, with an additional discussion on possible implications for hydropower potential.
Material and methods:
In this paper, the analysis of drought for the period from 1961 to 2024 is based on the Standardized Precipitation Evapotranspiration Index (SPEI), which is calculated for Požega, a city in the continental part of Croatia. Results obtained with SPEI were compared with those from another drought index, the New Drought Index (NDI). Further analysis of both indices across all time scales is provided using the RAPS (Rescaled Adjusted Partial Sums) method, and, based on the obtained sub-periods, daily discharges of the Orljava River are analyzed, and an index representing hydrological drought, Standardized Streamflow Index (SSI), for the Orljava River (station Požega) is also calculated.
Results and conclusions:
The results showed that there are two statistically different subperiods regarding drought occurrence: from 1961 to 1999 and from 2000 to 2024. The second subperiod is characterized by lower SPEI and NDI values, indicating more severe drought conditions. Based on daily discharges from the Orljava River, discharges are calculated for the entire period and for two subperiods identified through drought analysis, corresponding to 50% and 70% probability of occurrence. The lowest discharges are observed during the second subperiod, which is also characterized by more intense drought conditions. These results underscore the significance of drought and indicate possible constraints for hydropower development.
The aim of the study is to analyze the occurrence of drought in Požega, its temporal evolution, and its influence on daily discharges of the Orljava River, which flows through Požega, with an additional discussion on possible implications for hydropower potential.
Material and methods:
In this paper, the analysis of drought for the period from 1961 to 2024 is based on the Standardized Precipitation Evapotranspiration Index (SPEI), which is calculated for Požega, a city in the continental part of Croatia. Results obtained with SPEI were compared with those from another drought index, the New Drought Index (NDI). Further analysis of both indices across all time scales is provided using the RAPS (Rescaled Adjusted Partial Sums) method, and, based on the obtained sub-periods, daily discharges of the Orljava River are analyzed, and an index representing hydrological drought, Standardized Streamflow Index (SSI), for the Orljava River (station Požega) is also calculated.
Results and conclusions:
The results showed that there are two statistically different subperiods regarding drought occurrence: from 1961 to 1999 and from 2000 to 2024. The second subperiod is characterized by lower SPEI and NDI values, indicating more severe drought conditions. Based on daily discharges from the Orljava River, discharges are calculated for the entire period and for two subperiods identified through drought analysis, corresponding to 50% and 70% probability of occurrence. The lowest discharges are observed during the second subperiod, which is also characterized by more intense drought conditions. These results underscore the significance of drought and indicate possible constraints for hydropower development.
| ISSN: | 1644-0765 |
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