Spatiotemporal Variations of Meteorological Drought in Türkiye and Its Linkage With Large-Scale Atmospheric Circulation

In this study, long-term variations of dry and wet events, and large-scale atmospheric circulation mechanisms triggering drought conditions are investigated for T & uuml;rkiye. For this purpose, meteorological data of 92 stations are used for the period 1965-2020. For drought conditions, 0.5 degrees x 0.5 degrees monthly gridded values of the Standardised Precipitation Evapotranspiration Index (SPEI-1 month) are used for the period 1903-2022. Later, the role of North Atlantic Oscillation (NAO) and East Atlantic/West Russia (EA/WR) patterns on regional dry/wet seasons is investigated. Synoptic mechanisms causing extreme dry/wet events in the Aegean Region (AR) of T & uuml;rkiye are examined using NCEP/NCAR Reanalysis data. According to the main results, statistically significant negative trends of SPEI-1 month values are observed, especially in the western (AR) and southern (Mediterranean: MeR and Southeastern Anatolia: SEAR) regions during the winter and summer seasons. Additionally, we have found that temperature increments lead to more frequent summertime drought events in these regions, particularly during July (correlation coefficient [r] results are -0.58, -0.60 and - 0.61 for AR, MeR and SEAR, respectively). The impact of the NAO on drought events is more significant during the winter and summer months. During the positive phases of winter NAO conditions, the Azores surface high is located over the eastern Mediterranean Basin and causes atmospheric blockage, resulting in severe drought conditions in western T & uuml;rkiye (precipitation in AR is 60% less than normal and regional temperature is 1.5 degrees C below normal). Conversely, during summer NAO (-) phases, light northerly winds transfer dry air from northern terrestrial regions to the AR as a result of the interaction between the expanded Azores surface high and the surface Asiatic monsoon low. Prolonged above-normal temperatures at low levels of the atmosphere and dry air at the surface result in more frequent and intense drought conditions over western T & uuml;rkiye (AR temperatures are 1.2 degrees C above normal). The results of this study can help managers understand the large-scale atmospheric role in the occurrence of meteorological drought and to cope with drought events by reducing drought impacts on different sectors.