Yazar "Keskin, Asli Ülke" seçeneğine göre listele

Listeleniyor 1 - 4 / 4
  • [ X ]
    Öğe
    Clustering of Black Sea Region Stations Using K-Means, Fuzzy C-Means and Silhouette Index Analysis Methods
    (Eskisehir Teknik Üniversitesi, 2023) Kir, Gürkan; Keskin, Asli Ülke; Zeybekoglu, Utku
    In recent years, there has been a noticeable increase in the number of disasters caused by the effects of global climate change. In this context, various studies are carried out in our country and in the world in order to reduce the effects of climate change. The classification of regions affected by climate change into similar classes in terms of climate parameters is important in terms of applying similar methods in studies to be carried out in these regions. Thus, a correct strategy will be determined in the studies to be carried out in order to reduce the effects of climate change. Within the scope of the study, annual temperature records of 31 stations in the Black Sea Region belonging to the Turkish State Meteorological Service for the period 1982-2020 were evaluated. Cluster analysis was carried out using the Fuzzy C-Means and K-Means methods. As a result of the study, the optimum number of clusters was determined by Silhouette index analysis. The most suitable classification for the temperature observations was obtained by the K-Means method by choosing the number of clusters as 5.
  • [ X ]
    Öğe
    Evaluation of The Homogeneity and Trends of Precipitation, Temperature and Wind Speed Parameters in The Black Sea Region
    (Hakan ÇAGLAR, 2023) Keskin, Asli Ülke; Kir, Gürkan; Zeybekoglu, Utku
    In recent years, there has been a noticeable increase in the number of disasters caused by the effects of global climate change. In this context, various studies are carried out in our country and in the world in order to reduce the effects of climate change. In the study, homogeneities and trends of precipitation, temperature and wind speed series of 31 stations in the Black Sea region were investigated. In addition, evaluations were made considering possible tendencies to disrupt homogeneity. In homogeneity analysis, Standard Normal Homogeneity Test (SNHT), Buishand Range Test (BRT), Pettitt Test (PT) and Von Neumann Ratio Test (VN), known as Absolute homogeneity tests, were used. Possible trends of stations were investigated using Spearman's Rho (SR) and Mann Kendall (MK) tests. According to the results of the homogeneity analysis, while the precipitation series of 30 stations were homogeneous, three stations were determined as homogeneous in the wind speed results. When the temperature series of the stations were examined, it was determined that the homogeneity was impaired in all stations. According to the results of the trend analysis, the significant increase trends determined especially in the temperature series show that the region started to warm up over time as an effect of global climate change.
  • [ X ]
    Öğe
    Hydrological and Meteorological Drought Forecasting for the Yesilirmak River Basin, Turkey
    (Hakan ÇAGLAR, 2021) Hezarani, Alyar Boustani; Zeybekoglu, Utku; Keskin, Asli Ülke
    Drought is the most dangerous natural disaster. It differs from the other disasters in that it occurs insidiously, its effects are revealed gradually, and it persists for a long period. Drought has huge, negative effects on both society and natural ecosystems. In this study, values from the Standardized Precipitation Index (SPI) were used to generate drought estimation models by using Artificial Neural Networks (ANN). In addition, the probability of hydrological drought was determined by using SPI values to predict Streamflow Drought Index (SDI) values with ANN. Also, the SPI and SDI were used as the meteorological and hydrological drought indices, respectively, in conjunction with Feed Forward Neural Networks (FFNN), in ANN models. For this purpose, three rainfall and three flow gauging stations located in the Yesilirmak River Basin of Turkey were selected as the study units. The SPI and SDI values for the stations were calculated in order to create ANN estimation models. Different ANN forecasting models for SPI and SDI were trained and tested. In addition, the effects of the spatial distribution of precipitation on flows were determined by using the Thiessen Method to develop the SDI prediction model. The results generated by the ANN prediction models and resulting values were compared and the performances of the models were analyzed. The combination of ANN and SPI predicted meteorological drought with high accuracy but the combination of ANN and SDI was not as good in predicting hydrological drought.
  • [ X ]
    Öğe
    Türkiye Yagis Siddeti Serilerinin Homojenlik Analizi
    (Hakan ÇAGLAR, 2022) Zeybekoglu, Utku; Keskin, Asli Ülke
    Bu çalismada, Meteoroloji Genel Müdürlügü tarafindan isletilen 103 istasyondan 30 ile 78 yil arasinda degisen periyotlar için yillik maksimum yagis siddeti serilerinin homojenlik kontrolü yapilmistir. Mutlak homojenlik testleri olarak bilinen Standart Normal Homojenlik Testi (SNHT), Buishand Aralik Testi (BRT), Pettitt Testi (PT) ve Von Neumann Oran Testi (VNRT) %95 güven araliginda uygulanmistir. Standart süre verilerinden en az biri süpheli veya sorunlu ise, istasyon homojen degil olarak siniflandirilmistir. Homojenligi bozan faktörün muhtemel trend bilesenleri oldugu varsayilarak, trend bilesenleri ayrilmistir. Daha sonra, yagis siddeti serilerin mutlak homojenlik testleri yeniden uygulanmistir. Analizler sonucunda 103 istasyonun 49'u 14 standart sürenin tamaminda kullanilabilir olarak siniflandirilmistir. Kalan 54 istasyonun 45'i, trend bilesenlerinden sonra tüm standart süreleri kullanilabilir olarak siniflandirilmistir. 103 istasyondan geriye kalan 8’inde ise trend bilesenleri ayrildiktan sonra homojen olmayan degerlere sahip oldugu tespit edilmistir.