Yazar "Geyikli, Mehmet Selim" seçeneğine göre listele

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    Accuracy Evaluation of Standardized Precipitation Index (SPI) Estimation under Conventional Assumption in Yeşilirmak, Kizilirmak, and Konya Closed Basins, Turkey
    (Hindawi Limited, 2023) Hınıs, Mehmet Ali; Geyikli, Mehmet Selim
    The doubt in the calculation algorithm of the standardized precipitation index (SPI), which is widely preferred in the evaluation and monitoring of drought, still remains up-to-date because its calculation process is performed in the form of standardization or normalization with a default probability distribution. Therefore, the success of this index is directly affected by the choice of the probability distribution model. This study is based on the effect of three different parameter estimation methods on the calculation process, as well as the comparison of the SPI results calculated based on the default Gamma distribution and the distribution with the best ability to represent the 3-and 12-month consecutive summed rainfall data among the 15 candidate distributions namely Gamma (GAM), Generalized Extreme Value (GEV), Pearson Type III (P III), Log Pearson Type III (LP III), two-parameter Lognormal (LN2), three-parameter Lognormal (LN3), Generalized Logistic (GLOG), Extreme Value Type I (EVI), Generalized Pareto (GPAR), Weilbul (W), Normal (N), Exponential (EXP), Logistic (LOG), four-parameter Wakeby (WK4), and five-parameter Wakeby (WK5) distributions. Approximately 68.4% and 18.4% of the 3-month data considered had the best fit to the Weibull and Pearson III distribution, while approximately 24% and 18% of the 12-month data had the best fit to the Weibull and Logistic distribution. On the other hand, it was found that the default Gamma distribution calculated the extreme drought categories significantly more than the best-fit distribution model. In terms of parameter estimation methods, L-moments for 3-month series and maximum likelihood approaches for 12-month series were most dominant.
  • Küçük Resim
    Öğe
    Drought analysis with two different ındices in yeşilırmak basin
    (Tokat Gaziosmanpaşa Üniversitesi Ziraat Fakültesi Dergisi Yayın Ofisi, 2022) Geyikli, Mehmet Selim; Hınıs, Mehmet Ali; Yürekli, Kadri
    Reducing the negative effects of drought disaster, which is one of the most important parameters affecting the planning and management of water resources, has become very important today. Many methods have been proposed in the literature for the calculation of drought, which is used to express the periods when precipitation is significantly less than the average, and two of these methods, "Standardized Precipitation Index (SPI)" and "Reconnaissance Drought Index (RDI)" were applied to the Yeşilırmak basin in this study.12-month SPI and RDI analyzes were made and compared by using the monthly precipitation and evapotranspiration totals of 8 stations in the Yeşilırmak Basin for the period 1991-2020. The results show us that the SPI and RDI methods generally give similar signals for wet periods, but the RDI method defines more extreme dry periods than the SPI method in extreme dry periods. While the RDI method defines more extreme dry periods than the SPI method; It was observed that the SPI method defined more extreme wet periods than the RDI method. In drought analysis, using an index based on more than one meteorological parameter (such as the RDI) will give more reliable results instead of using an index based on a single parameter (i.e, SPI). It has shown in this study that the effect of evapotranspiration values in drought calculation is very important by comparing it with RDI analysis and SPI analysis.