[PP13] Hydrological droughts of groundwater 
[PP13] Hydrological droughts of groundwater
Key message
The frequency and intensity of groundwater droughts in alluvial aquifers have been increasing in recent decades. 8 out of 10 driest years in the 1981-2025 period occurred after year 2000. Higher intensity droughts generally occur in winter while milder droughts are characteristics of autumn. However, in the Primorska region and Ljubljana basin, extreme droughts predominately occur in summer. An increasing trend in extreme drought intensity is evident between June and September, coinciding with periods of peak water demand.
Charts
Figure PP13-1: Annual average of standardized groundwater level index (SGI) on selected measuring stations
Sources:
Hydrologic database ARSO, Slovenian Environment Agency (30. 01. 2026)
Table PP13-2: Percentage of measuring stations with groundwater drought detection in intergranular aquifers by individual years
Sources:
Hydrologic database ARSO, Slovenian Environment Agency (30. 01. 2026)
| Extremely dry (SGI <-2)[%] | Severely dry (-2 <SGI <-1.5)[%] | Moderately dry (-1.5 <SGI <-1)[%] | Mildly dry ( (-1 < SGI < 0)[%] | |
|---|---|---|---|---|
| 1981 | 1.06 | 4.26 | 8.51 | 24.47 |
| 1982 | 1.96 | 2.94 | 6.86 | 25.49 |
| 1983 | 5.83 | 8.33 | 16.67 | 22.50 |
| 1984 | 0 | 3.92 | 9.80 | 23.53 |
| 1985 | 1.59 | 4.76 | 11.90 | 20.63 |
| 1986 | 0 | 1.63 | 8.94 | 20.33 |
| 1987 | 0.92 | 0.92 | 10.09 | 21.10 |
| 1988 | 1.05 | 2.11 | 10.53 | 26.32 |
| 1989 | 2.44 | 8.94 | 17.07 | 21.95 |
| 1990 | 0.93 | 3.70 | 14.81 | 28.70 |
| 1991 | 0.91 | 1.82 | 2.73 | 22.73 |
| 1992 | 0 | 2.75 | 19.27 | 27.52 |
| 1993 | 2.31 | 15.38 | 23.08 | 23.85 |
| 1994 | 0 | 1.06 | 5.32 | 27.66 |
| 1995 | 0.81 | 1.61 | 6.45 | 21.77 |
| 1996 | 0 | 1.04 | 1.04 | 11.46 |
| 1997 | 1.05 | 7.37 | 20 | 32.63 |
| 1998 | 0 | 3.42 | 14.38 | 21.23 |
| 1999 | 0 | 1.72 | 7.76 | 18.97 |
| 2000 | 0 | 4.17 | 22.92 | 31.25 |
| 2001 | 1.69 | 11.02 | 15.25 | 26.27 |
| 2002 | 6.48 | 20.37 | 21.30 | 23.15 |
| 2003 | 8.33 | 24.07 | 26.85 | 25.93 |
| 2004 | 4.27 | 8.55 | 11.11 | 24.79 |
| 2005 | 0 | 1.59 | 12.70 | 24.60 |
| 2006 | 3.03 | 6.06 | 15.91 | 21.97 |
| 2007 | 3.85 | 7.69 | 23.08 | 29.81 |
| 2008 | 0 | 1.05 | 10.53 | 32.63 |
| 2009 | 0.81 | 1.63 | 9.76 | 21.14 |
| 2010 | 0 | 0 | 6.67 | 22.86 |
| 2011 | 1.60 | 10.40 | 22.40 | 24.80 |
| 2012 | 4.88 | 18.70 | 23.58 | 23.58 |
| 2013 | 0 | 2.11 | 7.04 | 19.01 |
| 2014 | 0 | 0 | 0 | 15.56 |
| 2015 | 0 | 3.19 | 12.77 | 29.79 |
| 2016 | 0 | 3.06 | 14.29 | 30.61 |
| 2017 | 0.91 | 8.18 | 20 | 28.18 |
| 2018 | 0.78 | 2.33 | 9.30 | 22.48 |
| 2019 | 1.87 | 8.41 | 20.56 | 28.97 |
| 2020 | 1.77 | 9.73 | 20.35 | 27.43 |
| 2021 | 0 | 5.26 | 15.79 | 27.19 |
| 2022 | 7.77 | 16.50 | 24.27 | 26.21 |
| 2023 | 0 | 0 | 2.21 | 16.91 |
| 2024 | 0.97 | 0.97 | 6.80 | 25.24 |
| 2025 | 1.15 | 4.60 | 19.54 | 35.63 |
Figure PP13-3: Percentage of measuring stations with groundwater drought detection in intergranular aquifers between June and September by individual years
Sources:
Hydrologic database ARSO, Slovenian Environment Agency (30. 01. 2026)
| Extremely dry (SGI <-2)[%] | Severely dry (-2 <SGI <-1.5)[%] | Moderately dry (-1.5 <SGI <-1)[%] | Mildly dry ( (-1 < SGI < 0)[%] | |
|---|---|---|---|---|
| 1981 | 2.08 | 2.08 | 4.17 | 22.92 |
| 1982 | 0 | 0 | 5.56 | 40.74 |
| 1983 | 0 | 5.88 | 17.65 | 43.14 |
| 1984 | 0 | 1.75 | 1.75 | 24.56 |
| 1985 | 0 | 1.27 | 5.06 | 22.78 |
| 1986 | 0 | 1.33 | 0 | 18.67 |
| 1987 | 0 | 0 | 4.69 | 18.75 |
| 1988 | 0 | 0 | 3.64 | 27.27 |
| 1989 | 0 | 0 | 0 | 20.90 |
| 1990 | 0 | 0 | 5.08 | 42.37 |
| 1991 | 0 | 0 | 2.70 | 21.62 |
| 1992 | 0 | 3.13 | 25 | 45.31 |
| 1993 | 5.26 | 28.07 | 40.35 | 22.81 |
| 1994 | 0 | 0 | 3.64 | 38.18 |
| 1995 | 0 | 0 | 0 | 14.29 |
| 1996 | 0 | 0 | 0 | 7.94 |
| 1997 | 0 | 1.96 | 3.92 | 52.94 |
| 1998 | 0 | 3.95 | 18.42 | 34.21 |
| 1999 | 0 | 0 | 0 | 13.16 |
| 2000 | 0 | 6.67 | 35.56 | 53.33 |
| 2001 | 0 | 0 | 8.93 | 46.43 |
| 2002 | 0 | 9.23 | 18.46 | 32.31 |
| 2003 | 9.43 | 37.74 | 39.62 | 9.43 |
| 2004 | 0 | 0 | 2.99 | 37.31 |
| 2005 | 0 | 0 | 1.12 | 30.34 |
| 2006 | 0 | 1.54 | 1.54 | 24.62 |
| 2007 | 3.51 | 7.02 | 29.82 | 42.11 |
| 2008 | 0 | 0 | 3.08 | 23.08 |
| 2009 | 0 | 1.32 | 1.32 | 18.42 |
| 2010 | 0 | 0 | 10.77 | 30.77 |
| 2011 | 0 | 0 | 13.33 | 62.22 |
| 2012 | 0 | 20 | 32.73 | 32.73 |
| 2013 | 0 | 3.90 | 6.49 | 27.27 |
| 2014 | 0 | 0 | 0 | 18.18 |
| 2015 | 0 | 0 | 8.33 | 41.67 |
| 2016 | 0 | 0 | 3.70 | 44.44 |
| 2017 | 1.47 | 7.35 | 25 | 41.18 |
| 2018 | 0 | 0 | 1.39 | 22.22 |
| 2019 | 0 | 1.54 | 9.23 | 36.92 |
| 2020 | 1.56 | 9.38 | 14.06 | 34.38 |
| 2021 | 0 | 0 | 7.14 | 42.86 |
| 2022 | 13.33 | 15 | 26.67 | 33.33 |
| 2023 | 0 | 0 | 0 | 7.14 |
| 2024 | 0 | 0 | 1.69 | 13.56 |
| 2025 | 2.08 | 2.08 | 25 | 54.17 |
Methodology
Other sources and literature
- Agencija RS za okolje, 2018. Ocena podnebnih sprememb v Sloveniji do konca 21. stoletja. Ljubljana, november 2018.
- Kobold, M., 2003/2004. Hidrološka suša slovenskih vodotokov v obdobju 2000 – 2002. Ujma, 23: 128-135.
- Mckee, T. B., Doesken, N. J. & Kleist, J., 1993: The relationship of drought frequency and duration to time scales. Eight Conference on Applied Climatology: 179–184.
- WMO & GWP, 2016: Handbook of Drought Indicators and Indices (M. Svoboda and B.A. Fuchs). Integrated Drought Management Tools and Guidelines Series 2. Geneva.
- RSRS – Računsko sodišče Republike Slovenije, 2019: Revizijsko poročilo, Učinkovitost dolgoročnega ohranjanja virov pitne vode. Številka: 320-7/2017/30.
- Sheffield J., and Wood E.F., 2011: Drought: past problems and future scenarios. Earthscan, 210 pp.