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    Assessment of Drought Indices Based on Effective Precipitation: A Case Study from Çanakkale, a Humid Region in Türkiye
    (Mdpi, 2025) Saracoglu, Fevziye Ayca; Kaynar, Yusuf Alperen
    This study investigates the influence of different effective precipitation (P-e) estimation methods on drought index performance in a humid region of T & uuml;rkiye. The standard precipitation index (SPI) and the reconnaissance drought index (RDI) were compared with their effective precipitation-based counterparts, Agricultural Standardized Precipitation Index (aSPI) and Effective Reconnaissance Drought Index (eRDI), using four P-e estimation methods: USBR (U.S. Bureau of Reclamation), USDA-(Simplified and CROPWAT) (U.S. Department of Agriculture), and FAO (Food and Agriculture Organization). Data from three closely located meteorological stations (& Ccedil;anakkale, Bozcaada, and G & ouml;k & ccedil;eada) were analyzed across multiple time scales (1-, 3-, 6-, 12-month, and annual). Statistical metrics-coefficient of determination (R-2), root mean square error (RMSE), and Nash-Sutcliffe efficiency (NSE)-were used to assess the indices, and trend analyses were conducted using the Mann-Kendall and Sen's Slope tests. The USDA-Simplified method consistently showed the highest accuracy across all stations and time scales (R-2 approximate to 0.99; lowest RMSE approximate to 0.09; NSE > 0.95), while the FAO method performed poorly, particularly at the 1-month scale. Drought frequency and severity were found to increase with time scale, contrary to trends observed in arid regions. Trend analysis revealed no significant changes at short time scales, but statistically significantly increasing drought severity was detected in longer scales, especially in & Ccedil;anakkale, with slopes reaching up to -0.018 per year. The findings highlight the importance of selecting appropriate P-e estimation methods for accurate drought assessment, even in humid climates, and support the use of aSPI and eRDI with the USDA-Simplified method.
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    Evaluating the performance of three different gridded precipitation datasets by comparing the measurement dataset in the Susurluk basin
    (Gazi Univ, 2025) Saracoglu, Fevziye Ayca; Saracoglu, Kebir Emre
    In recent years, the need for long-term precipitation datasets that accurately represent spatiotemporal distribution has significantly increased. To meet this need, various gridded precipitation datasets have been developed. However, before utilizing these datasets, their accuracy must be assessed by comparing them with measurement datasets. For this purpose, the performance of three different monthly gridded precipitation datasets (Climatic Research Unit (CRU), Global Precipitation Climatology Center (GPCC) and University of Delaware (UDEL)) was evaluated in the Susurluk Basin over the period 1966-2017 at monthly, seasonal, and annual scales. The measurement dataset was obtained from six meteorological stations (Band & imath;rma, Bursa, Dursunbey, Keles, Simav, and Tav & scedil;anl & imath;) operated by the Turkish State Meteorological Service. The agreement between gridded and measurement datasets was assessed using statistical indexes such as the Coefficient of Determination (R2), Root Mean Square Error (RMSE), Mean Bias Error (MBE), and Nash-Sutcliffe Efficiency Index (NSE). Among the gridded datasets, GPCC demonstrated the best overall performance, while CRU showed the lowest performance. Additionally, it was observed that the gridded datasets exhibited higher consistency with measurement dataset in low-altitude regions. During wet seasons (winter and autumn), gridded precipitation datasets showed better agreement with the measurement dataset.
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    LOCAL SCOUR AROUND THE SIDE -WEIR ON COHESIVE BED MATERIAL
    (Parlar Scientific Publications (P S P), 2022) Saracoglu, Fevziye Ayca; Agaccioglu, Hayrullah
    The scour process and dimensionless equilibrium scour depths around the rectangular side weir have been studied for the non -cohesive bed material, extensively. In this experimental study, scour of cohesive materials in the vicinity of a rectangular side weir is studied for the first time, 38 runs including different combinations of upstream Froude Number, the length of side -weir, the side weir crest height, water content, clay content and bed shear strength has been conducted for this purpose. Experimental parameters are determined based on a dimensional analysis. Only subcritical flow conditions in a rectangular channel have been considered in this study. The bottom shear strength of cohesive sediment increases with the consolidation time hence the scour depths decrease with consolidation time. The scour depth increased rapidly with time and then asymptotically approached constant values with similar behavior to non -cohesive bed material. For all side weir dimensions, dimensionless scour depths increase with increasing the upstream Froude number and decrease with increasing the side -weir crest height where non -cohesive bed material act similarly. The scour depths has been found to be much smaller for the cohesive bed material when compared to non cohesive material for even stronger stream conditions. A regression equation is proposed for dimensionless equilibrium scour depths depending on dimensionless parameters for cohesive bed,
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    Van Gölü Su Yüzeyi Sıcaklıklarının Eğilim Analizi
    (2022) Saracoglu, Kebir Emre; Saracoglu, Fevziye Ayca
    Bu çalışmada, Van Gölü su yüzeyi sıcaklıklarının değişimi ve eğilimi araştırılmıştır. 2016-2020 tarih aralığı için; NASA-Gündüz, NASA-Gece uydu verileri ile Meteoroloji Genel Müdürlüğü’nden (MGM) 3 istasyon için edinilmiş olan ölçüm verileri karşılaştırılmıştır. Ayrıca gündüz ve gece uzun dönem uydu verilerinin (2001-2020) Theil-Sen ve Yenilikçi Eğilim Analizi yöntemleriyle aylık, yıllık (minimum-ortalama-maksimum) ve mevsimsel eğilim analizleri ile anlamlılık seviyeleri belirlenmiştir. 2016-2020 tarih aralığını kapsayan MGM ölçüm verileri ile NASA-Gündüz/NASA-Gece uydu verilerinin oldukça uyumlu olduğu belirlenmiştir (R=0,94-0,99). NASA-Gece su yüzeyi sıcaklıkları MGM ölçüm verileri ile daha uyumludur. 2001-2020 tarih aralığı için NASA-Gündüz ve NASA-Gece su yüzeyi sıcaklık verilerinin %1 anlamlılık düzeyinde homojen olduğu belirlenmiştir. Hem kısa hem de uzun dönemde su yüzeyi sıcaklıkları artış eğilimindedir. Aylık analizlerdeki en fazla artış (0,094 °C/yıl) gündüz verileri için Haziran ayında, gece verileri için (0,104 °C/yıl) Nisan ayında belirlenmiştir. Mevsimsel analizlerdeki en fazla artış ilkbahar mevsiminde gece verilerinde (0,080-0,099 °C/yıl) tespit edilmiştir. Uzun dönem yıllık ortalama su yüzeyi sıcaklığındaki ortalama artış 0,043 °C/yıl olarak hesaplanmıştır. Bu değerin, Doğu Karadeniz için belirlenmiş olan (0,11 °C/yıl) artıştan daha küçük, Ege ve Doğu Akdeniz için belirlenmiş olandan fazla (0,055°C/yıl), Güney Hazar Denizi için belirlenmiş olan artışın (0,029 ± 0,009 °C /yıl) yaklaşık 1,5 katı ve okyanuslar için belirlenmiş olan artışın (0,011 °C/yıl) yaklaşık 4 katı olduğu sonucuna varılmıştır.