Spatial and Temporal Linkages between Large-Scale Atmospheric Oscillations and Hydrologic Drought Indices in Turkey

In this study, spatial and temporal linkages between large-scale atmospheric oscillations (namely, North Sea–Caspian Pattern (NCP), North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Southern Oscillation (SO)) and hydrological droughts in Turkey are investigated. Monthly time indicators of the oscillations are described using the appropriate index, while streamflow indices computed from streamflow records in the period 1969–2004 at 96 gauge stations in Turkey are applied to define the hydrological drought indicator. To obtain more precise estimations of the Standardized Streamflow Index (SSI), various probability distributions are fitted and compared. Simultaneous and lagged cross-correlation analyses are then conducted to evaluate the spatial and temporal distribution of the connections between the oscillations and SSI values. Monthly correlation maps obtained from ArcGIS software demonstrate that the linkages between the NCPI and SSI are more significant during January/February/March and April. The results also show that the high value of negative correlations is most dominant in the western regions of Turkey, while the remarkable value of positive correlations is more dominant in the northeast part of Turkey. The significant negative correlations between NAOI/AOI and SSI values are mostly observed in the winter and early spring months. The impact of these oscillations is mainly dominant in the west, southwest, and northwest parts of the country. Moreover, the linkages between SOI and SSI are found to be more significant at higher lags (lag-two and lag-three) and the negative correlations are mostly detected.