Wavelet-based variability on streamflow at 40-year timescale in the Black Sea region of Turkey

Under the effects of human activities and climate change, severe changes of stream discharge are observed in large river basins in the world. Accordingly, assessing the temporal variability in streamflow is crucial for better water resources planning and management. Thus, the aim of the present study was to perform monthly streamflow analyses using the wavelet transform and descriptive statistics. Temporal variability of streamflow data of nine stations (Yakabasi, Derecikviran, Durucasu, Sutluce, Kale, Gomeleonu, Simsirli, Tozkoy, and Topluca) for period of 1964-2007 to study the influence of climatic oscillations over the Black Sea Region of Turkey was analyzed. Although all studied time series presented annual periodicity, Kale, Gomeleonu, Simsirli, Tozkoy, and Topluca stations presented a semi-annual signal as well. However, some discontinuities in the annual periodicity were found in the Durucasu, Sutluce, and Kale time series between 1964 and 2007. Finally, the scale-average wavelet power time series for each station studied were used to perform a cluster analysis, and it was observed that Topluca station presented a particular spectrum or could form an isolate cluster together with Simsirli and Tozkoy stations, mainly due to the intermittent oscillations on the annual frequency observed after 1990.