Comparative hydrological analysis stations on the boundary River Sotla/Sutla (Slovenia–Croatia)

Bonacci, Ognjen (author), Žaknić-Ćatović, Ana (author), Roje-Bonacci, Tanja (author)

This study examines hydrological processes at the Zelenjak (1958–2023) and Rakovec (1926–2022) stations on the Sotla/Sutla River, analyzed on an annual time scale. The analysis includes time series of annual minimum and maximum mean daily flows and mean annual flows. Additionally, data on annual precipitation and mean annual temperatures measured at the climatological station Bizeljsko in the period 1951 to 2024 were used to calculate annual runoff coefficients at the Zelenjak and Rakovec stations. The New Drought Index (NDI) was calculated using precipitation and air temperature data measured at the Bizeljsko climatological station. All analyses indicated a strong variability of the analyzed parameters over the available data period. A clear downward trend in mean annual flows is observed. In the recent period, from 2000 onward, there has been a sharp increase in mean annual air temperatures and a decline in all other analyzed hydrological and climatological parameters. Particularly concerning is the notable rise in the frequency and intensity of droughts in the 2000–2024 period. The causes of these trends could not be reliably determined through an analysis conducted on an annual time scale. It appears that natural factors, particularly the sharp rise in air temperatures, have played a significant role. However, it is important to emphasize that the natural characteristics of the Sotla/Sutla River basin have, to date, remained largely unaffected by human interventions. Furthermore, the insufficient accuracy in defining peak flows must be considered, as the rating curves used to define maximum flows may not have been reliable in certain periods.

• Language: English
• Keywords: flow, air temperature, precipitation, Sotla River, Zelenjak gauging stations, Rakovec gauging stations, climatological station Bizeljsko
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: Str. 15-27
• Numbering: Vol. 38, no. 68
• PID: 20.500.12556/RUL-171321
• UDC: 551.58:556.5(282)(497.4)(497.5)
• ISSN on article: 0352-3551
• DOI: 10.15292/acta.hydro.2025.02
• COBISS.SI-ID: 246340099
• Publication date in RUL: 22.08.2025

Record is a part of a journal

• Title: Acta hydrotechnica
• Publisher: Fakulteta za gradbeništvo in geodezijo
• ISSN: 0352-3551
• COBISS.SI-ID: 3664386

Licences

• License: CC BY-NC-SA 4.0, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International
• Link: http://creativecommons.org/licenses/by-nc-sa/4.0/
• Description: A Creative Commons license that bans commercial use and requires the user to release any modified works under this license.

Secondary language

• Language: Slovenian
• Title: Primerjalna hidrološka analiza na dveh postajah ob mejni reki Sotla/Sutla (Slovenija–Hrvaška)

Abstract

Študija preučuje hidrološke procese na postajah Zelenjak (1958–2023) in Rakovec (1926–2022) na reki Sotli/Sutli, analizirane na letni ravni. Analiza zajema časovne vrste najmanjših in največjih letnih srednjih dnevnih pretokov ter srednjih letnih pretokov. Podatki o letnih padavinah in srednjih letnih temperaturah zraka, zabeleženih na klimatološki postaji Bizeljsko v obdobju 1951–2024, so bili uporabljeni tudi za izračun letnih količnikov odtoka na postajah Zelenjak in Rakovec. Novi indeks suše (NDI) je bil izračunan na podlagi podatkov o padavinah in temperaturi zraka, izmerjenih na klimatološki postaji Bizeljsko. Vse analize so pokazale izrazito spremenljivost analiziranih parametrov v obdobju razpoložljivih podatkov. Opazen je izrazit trend upadanja srednjih letnih pretokov. V zadnjem obdobju, od leta 2000 naprej, je prišlo do izrazitega dviga srednjih letnih temperatur zraka ter upada vseh drugih analiziranih hidroloških in klimatoloških spremenljivk. Še posebej zaskrbljujoče je znatno povečanje pogostosti in intenzivnosti suš v obdobju 2000–2024. Vzrokov za te trende ni bilo mogoče zanesljivo določiti z analizo na letnem časovnem nivoju. Kaže, da so imeli pomembno vlogo naravni dejavniki, predvsem močan dvig temperature zraka. Vendar je treba poudariti, da naravne značilnosti porečja reke Sotla/Sutla do danes v veliki meri niso bile spremenjene zaradi antropogenih vplivov. Poleg tega je treba upoštevati nezadostno natančnost pri določanju koničnih pretokov, saj pretočne krivulje, uporabljene za določanje maksimalnih pretokov, v določenih obdobjih morda niso bile zanesljive.

• Keywords: pretok, temperatura zraka, padavine, reka Sotla, merilna postaja Zelenjak, merilna postaja Rakovec, klimatološka postaja Bizeljsko

Projects

• Funder: Government of Croatia and European Union
• Funding programme: Competitiveness and Cohesion Operational Programme
• Project number: KK.01.1.1.02.0027