Drought causes huge losses in agriculture and has many negative influences on natural ecosystems. In this study, the applicability of Adaptive Neuro-Fuzzy Inference System (ANFIS) for drought forecasting and quantitative value of drought indices, the Standardized Precipitation Index (SPI), is investigated. For this aim, 10 rainfall gauging stations located in Central Anatolia, Turkey are selected as study area. Monthly mean rainfall and SPI values are used for constructing the ANFIS forecasting models. For all stations, data sets include a total of 516 data records measured between in 1964 and 2006 years and data sets are divided into two subsets, training and testing. Different ANFIS forecasting models for SPI at time scales 1-12 months were trained and tested. The results of ANFIS forecasting models and observed values are compared and performances of models were evaluated. Moreover, the best fit models have been also trained and tested by Feed Forward Neural Networks (FFNN). The results demonstrate that ANFIS can be successfully applied and provide high accuracy and reliability for drought forecasting.

Trend analysis of precipitation and drought will play a significant role in the future development and sustainable management of water resources. It is the main purpose of this paper to analyse meteorological droughts and trends. The variability of the standardized precipitation index (SPI) was investigated at 1, 3, 6, 9, 12 and 24 monthly intervals. The trends of 1, 3, 6, 9, 12 and 24 monthly SPI results were analysed by applying linear regression and the Mann-Kendall and Spearman's rho tests at the 5% significance level. The linear slopes of the trends were calculated with a technique proposed by Sen. Meteorological data from eight meteorological stations in the Aegean region of Turkey were used for the period 1960-2013.The monthly precipitation trend decreases in December, January, February and March in all regions according to the linear regression analysis results. Annual precipitation decreased at five stations. In drought analysis by the SPI, in a short time period (such as 3 months) drought is more frequent but shorter, and as the period increases the duration of drought also increases but frequency decreases. Winter droughts are beginning to occur in the class of 'severe' in recent years. In this study carried out for different time periods according to SPI values in all stations, the highest ranges are in the normal and mild drought degrees. In addition, severe and extreme droughts are also seen intensely frequently. Trend analysis of precipitation and drought is compared. The trend analyses of precipitation are in parallel with the results of drought analyses.

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Natural disasters are important in human life. Drought is a disaster that depends on climatic and regional characteristics and affects all lives negatively. A detailed analysis of the region is necessary to determine the drought and take necessary measures. The researchers used different drought indices to determine drought. Standardized Precipitation Index (SPI) is one of the most commonly used drought indices that accounts different time scales. In this study, Bursa, Iznik, Keles, Mustafakemalpaşa, Uludag stations with long-term precipitation data in Bursa were examined for 1969-2015. The trend of precipitation data was determined by linear regression analysis. Precipitation data were standardized and evaluated according to the runs analysis. Lastly, drought analysis was performed for the periods 1, 3, 6, 9, 12, 24 and 48 months by the Standard Precipitation Index (SYI) method, which is widely used in our country and in the world. There was no significant trend in annual and monthly rainfall data. It was found that the monthly precipitation showed downward trend at Iznik, Keles, Uludag stations in December and at Bursa station in October. A statistically significant trend (5% risk) was not found in other months. Results of Standardized Precipitation Index are showed similarity which drought, normal and wet period rations in all stations. However, while normal or mild droughts are more frequent in short term periods (3-6 months), severe or very severe droughts have been observed over long term periods (12-24-48 months).