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 run-off expressed in million m³/year. Both elements are calculated on the basis of mean annual discharge (flow, Qs) of the water measuring stations catching the majority of inflow and run-off of river water in and from Slovenia. The balance of the river flow rates in 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 have a certain tradition, so that a longer temporal frame of comparable data is available for them. Upon accurate assessment of immediate anthropogenic effects on the river regime, the river balance may serve as a good indicator for the assessment of (potential) effects of climate changes on the quantities of available water.

Due to a rather high annual variability of river discharges, a longer temporal data frame is appropriate for trend assessment. According to the operating of the observed water gauging stations, we find as the most appropriate the frame which begins with the year 1961 and ends with 2000. When taking account of the entire frame of data (1961-2007) or a thirty-year period (1971-2000), the decreasing trend in river run-off is rather obvious, however, if we take account only of the period from 1981 to 2000, the trend is barely detectable.

Indirectly, the annual river run-off trends also recall the increase or decrease in the probability of low water (droughts) and flood hazard occurrences. However, the annual river run-off trends do not always correspond to trends of high or low water.