The above-average years 2013 and 2014 were followed by average year 2015 and average period 2016 – 2019 of annual runoff. In the year 2020 annual runoff was below-average. In the period 1961 - 2020, the driest years were 2011, 2007, 2003, 1983, and 1971. The long-term downward trend of river runoff from the territory of Slovenian currently persists.
This indicator shows the annual river balance of the Republic of Slovenia as a whole. The balance is composed of the river water inflow and runoff expressed in million m3/year. Both elements are calculated based on mean annual discharge (flow, Qs) at the water measuring stations catching the majority of inflow and runoff of river water in and from Slovenia. The river balance of Slovenia represents one of the fundamental and more dynamic elements of the Slovenian water balance, which is also composed of precipitation, evaporation, changes in groundwater reserves and water use. Discharge measurements are reliable and well-established, meaning a longer time series of comparable data is available. Based on the accurate assessment of direct anthropogenic effects on the river regime, the river balance may serve as a good indicator of potential effects of climate change on the quantities of available water.
Hydrological database, Slovenian Environment Agency ( February 2022)
Unit | 1961 | 1962 | 1963 | 1964 | 1965 | 1966 | 1967 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | 1978 | 1979 | 1980 | 1981 | 1982 | 1983 | 1984 | 1985 | 1986 | 1987 | 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | |
inflow | million m3/year | 12453 | 15163 | 14629 | 11969 | 20300 | 16564 | 14929 | 12715 | 12858 | 15595 | 9408 | 16409 | 12512 | 12081 | 16325 | 11028 | 13551 | 12898 | 16075 | 14103 | 12652 | 13152 | 11069 | 11965 | 12754 | 13098 | 14189 | 12499 | 13414 | 11602 | 14611 | 13736 | 12566 | 12033 | 11746 | 14737 | 11706 | 12344 | 13873 | 14299 | 11586 | 11458 | 9253 | 13086 | 12938 | 11821 | 10550 | 11639 | 16834 | 13362 | 11134 | 14868 | 15312 | 18996 | 12028 | 13442 | 11572 | 14537 | 13370 |
total run-off | million m3/year | 28699 | 35475 | 33294 | 29531 | 45265 | 33854 | 29115 | 28472 | 31449 | 33382 | 21601 | 36552 | 26541 | 28743 | 32543 | 26566 | 29571 | 29262 | 35669 | 32300 | 26077 | 29880 | 22087 | 28633 | 28763 | 28177 | 31944 | 26871 | 26557 | 26188 | 30235 | 28802 | 25296 | 25725 | 28176 | 32994 | 24027 | 28092 | 29659 | 30263 | 26912 | 24785 | 18353 | 30492 | 26837 | 24967 | 22213 | 27946 | 33875 | 34576 | 21122 | 28903 | 35204 | 43771 | 24073 | 30292 | 26797 | 30413 | 29091 |
net run-off | million m3/year | 16246 | 20312 | 18666 | 17562 | 24965 | 17291 | 14186 | 15758 | 18591 | 17787 | 12193 | 20143 | 14029 | 16661 | 16218 | 15538 | 16020 | 16365 | 19593 | 18198 | 13425 | 16727 | 11018 | 16668 | 16008 | 15078 | 17755 | 14372 | 13143 | 14587 | 15623 | 15066 | 12729 | 13692 | 16431 | 18257 | 12321 | 15748 | 15786 | 15964 | 15326 | 13327 | 9100 | 17405 | 13899 | 13146 | 11663 | 16307 | 17041 | 21214 | 9988 | 14035 | 19892 | 24775 | 12045 | 16851 | 15225 | 15876 | 15721 |
Due to a great annual variability of river discharges, a longer time series of data is required for trend assessment. According to the operation of relevant water gauging stations, the most appropriate time series would be 1961–2020. Throughout the period, a declining trend in total river runoff was observed. In the thirty-year period 1971–2000, the decline in river runoff is obvious. In the period 2000 - 2020, there is a characteristic deviation from the average in both directions, and the general tendency of decreasing runoff is less pronounced. River runoff trends indirectly indicate an increased or decreased probability of low water occurrence (drought) and flood risk. However, annual river runoff trends do not always correspond to trends of high or low water level.
Most Slovenian rivers have torrential characteristics. This means that discharges tend to increase and decrease very quickly and that most water runs off at high water levels or during flooding. In most rivers, high water occurs in spring and autumn, usually as a result of thaws, snow melting and abundant precipitation. Intensive local precipitation causes local flooding of a torrential character that only affect smaller catchment areas. Torrential watercourses are particularly vulnerable during periods of low discharge and hydrological drought, which are not distinctly seasonal and usually occur in late summer or early autumn. Hydrological droughts coincide with long periods of below-average precipitation and high air temperatures, which also results in agricultural droughts. As ecologically acceptable river discharges are maintained during such periods, shortages of irrigation water as well as deterioration of water quality may occur.
The above-average years 2013 and 2014 were followed by average year 2015 and average period 2016 – 2019 of annual runoff. In the year 2020 annual runoff was below-average. In the period 1961 - 2020, the driest years were 2011, 2007, 2003, 1983, and 1971. The long-term downward trend of river runoff from the territory of Slovenian currently persists.
Data methodology for this indicator
The methodology of monitoring, checking, and processing hourly and daily water levels, discharge measurements, water level conversions into discharge, longitudinal equalizations and coordination is well-established. Mean annual discharges are calculated from mean daily discharges. It is estimated that the original data may differ from the actual values by ± 5%. Data on mean annual discharge (Qs) from gauging stations are the result of measurements and observations in the measuring network of national water monitoring (data from HPP Dravograd and HPP Formin, Dravske elektrarne Maribor are also taken into account).
2020 is the last year for which we have official (verified) data of discharge from gauging stations. As the state borders do not coincide with the borders (watersheds) of the catchments of gauging stations, the river inflow and outflow calculated from the flows of selected gauging stations and the actual river inflow and outflow of Slovenia are not consistent. We estimate that the data cover 93% of the territory of Slovenia. Coherence is different in different river basins - for Posavje, to which more than half of the country belongs, the coherence is 99%, less than 90% is only in the immediate hinterland of the Adriatic Sea without the Posočje, where it is about 50%. Data for the discharge of the Mura are coordinated with the Austrian Hydrological Service. At other gauging stations, which represent balance profiles for inflow or outflow to and from Slovenia, there are no such harmonizations.
Data sources
Data set |
Unit |
Souce (hyperlink to data) |
Period used
|
Data availability |
Data refresh rate |
Data capture date |
International comparability of the data set |
Annual river balance of Slovenia (net outflow as the difference between total outflow and inflow) |
million m3 / year
|
Hydrological database, Slovenian Environment Agency, 2022
|
1961-2020 |
February 2022 for the entire period |
Once per year |
25.2.2022 |
Yes |
Definition of the indicator
• Relevance of the indicator: 1
1 = global,
2 = EU,
3 = national
• Accuracy of data used: 1
1 = official data that are public and reported in accordance with EU law,
2 = information available to the public but not official,
3 = internal data
• Comparability over time (refers to data in graph / graphs): 1
1 = at least a 10-year data set,
2 = at least 5 years of data set
3 = less than 5-year data set
• Spatial comparability (refers to data on the map / maps): 1
1 = official spatial data, also available for levels lower than national,
2 = official spatial data at national level
3 = spatial data are available but not official