Evaluating flood frequency analysis of the rivers in the Skopje Basin, North Macedonia – Statistical distribution fitting and hydrological insights

Abstract

This study examines the flood frequency analysis (FFA) of four rivers in North Macedonia: Vardar, Treska, Lepenac, and Serava. The aim is to contribute to water resource management, flood risk mitigation, and resilience to climate change through detailed seasonal analysis. The most appropriate probability distributions were determined for each river: Pearson Type III (PIII) for the summer and winter seasons in the Vardar, PIII for summer, and Gamma for winter in the Treska, PIII for both seasons in the Lepenac, and PIII for summer and Log-Normal for winter in the Serava. For each distribution, discharge estimates were calculated for different return periods. The results show significant seasonal variations in discharge, especially for the Treska and Lepenac rivers. For the Treska, winter discharges are significantly higher than summer discharges in all return periods, indicating that winter conditions mainly determine the annual flood risk. The Lepenac shows a similar pattern with significantly higher discharges in winter. In contrast, the Vardar shows relatively constant discharges between summer and winter, suggesting a balanced seasonal contribution to the annual flood risk. The Serava shows less seasonal variation, indicating a less variable hydrological system.
These results emphasise the importance of considering both annual and seasonal variability in the FFA to improve the accuracy of flood risk assessments and support effective water resource management. This research highlights the need for customised flood frequency models that account for seasonal runoff patterns to improve prediction accuracy and provide information for strategic planning in the face of climate change.