Annual and Low-Flow Trends in Serbia

This study analyzed the annual and low-flow trends of rivers located in Serbia, a part of southeast Europe. To achieve this, a comprehensive framework for flow trend estimation was established using both the conventional Mann-Kendall trend test and its modified version, which considers the serial correlation of flows, alongside the Theil-Sen trend estimator for modeling linear trends. The investigation was performed at a large spatial scale for sites of 80 hydrological stations with negligible human influence. The most important rivers are given as follows: the Velika Morava, Juzna Morava, Kolubara, Nisava, Timok, and Toplica rivers. Selected hydrological stations at these rivers drain the watershed areas from 79 km2 to 995 km2 with the respective recording periods (average length of the recorded data is equal to 60 years). The results implied that decreasing annual and low-flow trends are occurring for southern and eastern Serbian river streams while increasing trends were estimated at only a few hydrological sites. Hence, the results assist in revealing the most vulnerable river basins with statistically significant decreasing trends and provide a solid basis for the estimation of the design annual and low-flow trends in Serbia.