Changes in River Flow in Mediterranean Montenegro and Interaction with Variations in Atmospheric and Oceanic Oscillations

Due to the invaluable importance of the Morača River and its tributary the Zeta River for Montenegro, the aim of the study is to investigate changes in river flow based on data from 4 hydrological stations (HS) for the period 1961–2020, and to determine the influence of variations in atmospheric and oceanic oscillations on the hydroclimate (flow, air temperature and precipitation) of the observed area. Temperature and precipitation were considered based on data from 4 meteorological stations in the basin. All HS record a significant trend of decreasing monthly flows from April to August: ranging from – 4.1% to as much as – 20.8% per decade. The percentile method revealed that there was a significant increase in the annual number of days with low and very low flows (Qd < 9th percentile and Qd < 25th): up to 19.0 days per decade, while it decreased with high and very high flows (Qd > 75th and Qd > 91st): up to – 8.6 days per decade. According to the RAPS method, the turning point marking the onset of rapid flow reduction is the year 1980/1981. The impact of climate change is evident, but the results have also shown a statistically significant relationship between flow, precipitation, and temperature with variations in atmospheric and oceanic oscillations. The negative effect of worrying flow reduction, especially in summer, is already being felt, and as a warmer future is projected, additional implications for water resources management, agriculture, tourism, ecology, and other natural and social processes should be expected.