Trends in Turkish monthly mean streamflow

The research explored trends in monthly mean streamflow variables for a network of 57 Turkish streamflow gauging stations in 25 basins of Turkey. The procedure employs the Mann-Kendall rank correlation test to detect trends. The application of Mann-Kendall test resulted in the identification of significant decreasing trends at the 0.05 level appearing mostly in the basins in western Turkey whereas almost no evidence of significant change was experienced with a general downward direction in the rest of the country. Of the 57 stations, however, only 406, 712, 1226, 1402, 1517 and 2233 exhibited significant increasing trend over Turkey. The number of stations showing a decreasing trend is more than sevenfolds the number of stations with an upward trend, whereas the significant downtrend exceeded the uptrends by twentyfolds. Besides, more than half of the decreasing trends were found statistically significant while approximately 21% of the increasing trends exhibited significant trend. Hydrologically, these results indicate that Turkey is generally getting drier.