Performing drought analysis of basins with respect to global climate models

In terms of sustainable management of water resources, it is very important to accurately define the drought processes that occur with the decrease in precipitation. The drought process, which begins with precipitation below the long-term averages, is called meteorological drought. The drought process continues as a hydrological drought with the decrease in flow rates in streams because of the effect of meteorological drought. In case of prolonged and severe meteorological and hydrological droughts, it is inevitable that agricultural and socio-economic drought will occur as a result. For this reason, it is necessary to determine the characteristics of the meteorological and hydrological drought processes that occurred in the past in the basins, and to make the management planning of the water resources by predicting the possible drought processes in the future. In the present study, meteorological and hydrological droughts occurring at the 1, 3, 6 and 12-month time scales between 1970-2015 in the Acısu, Selendi, Murat, Medar, Gördes, Ahmetli, Demirci and Deliiniş sub-basins in the Gediz Basin were determined. In the determination of meteorological and hydrological droughts, index methods that gives fast and accurate results were used. Among these methods, the Standardized Precipitation Index (SPI) method and the Standardized Precipitation Evapotranspiration Index method were used in the defining of meteorological droughts, and the Standardized Runoff Index (SRI) method was used in the defining of hydrological droughts. The characteristic features of the meteorological and hydrological droughts occurring in the basins in the dry and wet periods were defined using the Run Theory Analysis method. After determining the past droughts seen in the basins in the study, possible meteorological droughts were estimated at 1, 3, 6 and 12-month time scales with SPI and SPEI index methods, using the precipitation and temperature data between the years 2015-2100 obtained from the EUR-11_ICHEC_EC_EARTH global climate model. The association between historical meteorological and hydrological droughts was used in the study to predict potential hydrological droughts between 2015 and 2100. This approach does away with the need to create a hydrological model to anticipate future flows. The relationship between meteorological and hydrological droughts in the basins in the prediction of future hydrological droughts was investigated in different combinations for 1, 3, 6 and 12 month time periods by using Feed Forward Backpropagation Artificial Neural Network, Generalized Regression Artificial Neural Network, Simple and Multiple Linear Regression Analysis methods. Possible hydrological droughts between 2015 and 2100 were estimated with the most appropriate method and input sets. As a result of the study, meteorological and hydrological droughts of Acısu, Selendi, Murat, Medar, Gördes, Ahmetli, Demirci and Deliiniş sub-basins in the Gediz basin were defined for 1, 3, 6 and 12 month time scales. As a result of the study, it has been shown that severe droughts were experienced in the basin in certain periods between 1970 and 2015 and evapotranspiration losses played a more active role in droughts after 2000. In the study, it is also predicted that until the middle of the 21st century, dry and wet periods will be experienced in meteorological and hydrological droughts, but dry periods will be felt more. It is shown in the study that towards the end of the second half of the 21st century, arid processes will be more dominant, and the duration and severity of very severe drought classes can be seen more.