Evaluation of Streamflow Drought Index in Aegean Region, Turkey Ayşe Gulmez 1* [0000-0002-3021-8655] , Denizhan Mersin 2 [0000-00012-9685-1499] , Babak Vaheddoost 3 [0000-0002-4767-6660] , and Mir Jafar Sadegh Safari 4 [0000-0003-0559-5261] 1 MSc Student. Department of Civil Engineering, Bursa Technical University, Bursa-Turkey. e-mail: 19262821008@ogrenci.btu.edu.tr 2 MSc. Department Civil Engineering, Izmir Institute of Technology, Izmir-Turkey. e-mail: denizhanmersin@iyte.edu.tr 3 PhD. Department of Civil Engineering, Bursa Technical University, Bursa-Turkey. e-mail: babak.vaheddoost@btu.edu.tr 4 PhD. Department of Civil Engineering, Yasar University, Izimr-Turkey. e-mail: jafar.safari@yasar.edu.tr Abstract. Water is an invaluable substance of which ensures the life cycle and hydrological events across the world. In this respect, water deficit also known as drought is a natural disaster related to water scarcity in time and space. Although there is no solid definition for the phenomenon, the outcome of repeated wet and dry spells cause in economic, social, and political problems at regional, country- wide, and world-wide scale. In this study, drought associated with the streamflow in the Aegean region, which has an important economic, historical and socio- cultural role in the western Turkey, is investigated through the well-known streamflow drought index (SDI). Therefore, average discharge in the Çiçekli -Nif, Beşdeğirmenler-Dandalas, Bebekler-Rahmanlar and Koçarlı-Köprübaşı station respectively related to on Gediz, Büyük Menderes and Küçük Menderes basins were used. Then SDI with 1, 3, 6,12 months moving average are acquired to express the drought severity associated with the streamflow in the basins. Results showed that the SDI values in all of stations together with the 1, 3, 6, and 12- month moving averages depicts similar results and no abnormal situation exist during the study period. Keywords: Aegean region, drought, streamflow drought index, hydrology 1 Introduction Water is the most vital commodity that ensures the life and hydrological cycle across the globe. For this, water deficit also known as drought can be distinguished as a natural disaster related to the long lasting dry spells across a region through time and space. To this end, there is no universally acceptable definition for the drought phenomenon mostly due to the diverse aspects and the outcome [1-3]. This disaster influences natural habitats, ecosystems, and various economic and social sectors, urban water supply, the