Hydrological drought associations with extreme phases of the North Atlantic and Arctic Oscillations over Turkey and northern Iran

Abstract

Impacts of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) on hydroclimatic variables have been previously studied in various viewpoints. This study adds a new perspective by focusing on the influences of winter NAO and AO extreme phases on hydrological drought using a standardized streamflow index (SSFI) over Turkey and northern Iran. Moreover, the physical mechanisms associated with the extreme phases of NAO over different atmospheric conditions were investigated. The results concerning short‐term droughts across Turkey revealed that wet conditions dominate particularly in the winter and following spring during the negative NAO and AO extreme phases while the NAO and AO impacts in Iran are only significant during simultaneous winter. Furthermore, the outputs of SSFI for the positive extreme phases of NAO and AO considerably differed in Turkey and Iran so that multiple drought events were detected in Turkey for all timescales as generally opposed to Iran. Western and eastern Turkey suffered from drought in various magnitudes during the positive extreme phases of NAO while fewer droughts were observed in Iran around the Caspian Sea during the negative NAO and AO extreme phases. Results of correlation analysis depicts that negative cycles are controlling wetness (drought) in Turkey (Iran) while there is a weak correlation between positive NAO cycles and SSFIs in the study area. In addition, our study showed that negative NAO and AO extreme phases could affect the hydrological drought stronger but in a shorter period compared with a longer period regarding the positive NAO and AO phases.