Interannual Variability of Reservoir Occupancy: A Multi-Reservoir Assessment from Çanakkale, Türkiye

Monitoring reservoir occupancy rates is increasingly important under rising water demand and growing hydrological variability. This study evaluates temporal variability in occupancy rates of seven reservoirs (Atikhisar, Ayvacık, Bakacak, Gökçeada, Taşoluk, Tayfur, and Umurbey) in Çanakkale Province (Türkiye) over the period 2013–2023. Bray–Curtis similarity and hierarchical cluster analyses were applied to assess interannual and inter-reservoir patterns, while Mann Kendall trend analysis, Sen’s slope estimator, and Spearman’s rank correlation were also applied to evaluate temporal trends and precipitation occupancy relationships. The results revealed interannual variability, with occupancy rates ranging from 2.7% to 79.2%. Gökçeada, Atikhisar, and Umurbey exhibited relatively similar occupancy dynamics, whereas Bakacak and Taşoluk displayed more distinct patterns. Trend analysis indicated that no statistically significant trends were observed for most reservoirs (p > 0.05), whereas a statistically significant decreasing trend was detected only for Umurbey Reservoir (Z = -2.14, p = 0.033; Sen’s slope = -2.45). Correlation analysis did not indicate a statistically consistent relationship between annual precipitation and reservoir occupancy (p > 0.05), despite moderate correlation coefficients in some reservoirs. These results indicate that annual precipitation alone does not adequately explain interannual variations in reservoir occupancy. Overall, reservoir occupancy appears to reflect the combined influence of hydroclimatic variability and other unquantified factors rather than a single controlling variable. The results provide a quantitative and comparative assessment of reservoir occupancy dynamics and may serve as a reference for future water management and research efforts in the region.