KAZALCI OKOLJA

Key message
Neutral

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.


Charts

Figure VD03-1: Annual river balance of Slovenia (net run-off as the difference between total run-off and inflow)
Sources:

Hydrological database, Slovenian Environment Agency ( February 2022)

Show data
  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

Goals

  • I
  • Improved assessments of water quantities.
  • Providing a sufficient amount of drinking water for inhabitants.
  • Better availability of water intended for use (in the sense of reducing the effects of hydrological droughts) and improved state of water and water ecosystems.

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.


Methodology

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

Date of data source summarization