Temporal changes in the Euphrates and Tigris discharges and teleconnections

The streamflow timings of the Euphrates and Tigris, two important snow-fed rivers in the Middle East, are found to be shifting to earlier days in the year. Six out of eight stations indicate statistically significant shifts between two consecutive 17-year periods (i.e. 1972-88 and 1990-2006). Among these stations, the average shift to earlier times is over 5 days, suggesting earlier spring melting of snowpack due to increased temperatures in the second period. A striking increase in the discharges takes place during the first half of March, and it is observed at all stream gauging sites considered in this study. An analysis based on the NCEP/NCAR reanalysis data indicates that warming which results in this increase is associated with the switching from the northeasterly flow to southwesterly flow over the Black Sea and western Anatolia caused by the weakening of the Siberian High over eastern Europe. These changes in the circulation features from the first to second periods are found to be very consistent with the positive and negative phases of the North Sea-Caspian pattern.