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Öğe Analysis of temperature and precipitation series of Hirfanli Dam Basin by Mann Kendall, Spearman’s Rho and Innovative Trend Analysis(Murat Yakar, 2024) Gunduz, Fatma; Zeybekoglu, UtkuIn this study long-term trend analysis of precipitation and temperature series are determined in the Hirfanli dam basin of Turkey. Data is obtained from the Turkish State Meteorological Service for the period of 1968 to 2017 for Gemerek, Kayseri, Kirsehir, Nevsehir, Sivas and Zara. Mann-Kendall, Spearman's Rho and Innovative Trend Analysis are used for trend analysis with 95% confidence levels. According to the results of the temperature series upward trend were determined. The results of all methods are similar but increasing significant trends were determined by Mann Kendall and Spearman's Rho except Zara. According to the precipitation series results, with decreasing trends in Gemerek, Kirsehir, Nevsehir and Zara, increasing trends were determined in Kayseri and Sivas. The results of Mann Kendall and Spearman's Rho methods show parallelism with each other. Contrary to other methods, Innovative Trend Analysis determined a decreasing trend in Kayseri. As a result of the analysis, the trends in the precipitation series are not significant at the 95% confidence level. In addition to statistical analyzes, evaluations were made in terms of integrated disaster management for drought disaster in the basin with arid climate characteristics. © 2024, Murat Yakar. All rights reserved.Öğe Assessment and monitoring of drought conditions in a TR82 region in Türkiye using precipitation-based drought indices: MCZI and PNI(Springer-Verlag Italia Srl, 2026) Zeybekoglu, UtkuDrought is a multifaceted phenomenon with meteorological, agricultural, and hydrological dimensions, often resulting in significant economic, social, and environmental impacts. As a key indicator of climate change, understanding drought patterns is essential for effective water resource management. This study investigates drought trends in T & uuml;rkiye's TR82 region by analyzing precipitation data from 10 meteorological stations over the period 1981-2023. Two precipitation-based drought indices, the Modified China-Z Index (MCZI) and the Percent of Normal Index (PNI), were applied to evaluate the spatiotemporal characteristics of drought in the region. Results reveal recurrent drought episodes, notably in 1981-82, 1985-86, 1989-90, 1992-94, 1996, 2003-04, 2006-08, 2013, 2017, 2020, and 2022, highlighting the persistent nature of drought in the TR82 region. The study demonstrates the effectiveness of MCZI and PNI for regional drought assessment and underscores the importance of proactive drought preparedness and strategic planning to mitigate future impacts in this climate-sensitive area.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, UtkuIn 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.Öğe Clustering of the Black Sea Region meteorological stations of Türkiye with fuzzy c-means, k-means, and silhouette index analysis methods by precipitation, temperature and wind speed(Hungarian Meteorological Service, 2025) Keskin, Asli Ulke; Kir, Gurkan; Zeybekoglu, UtkuRecent years have seen a marked increase in the number of disasters caused by the effects of global climate change. In response, a range of studies have been conducted in T & uuml;rkiye and worldwide with the aim of reducing the impact of climate change.The classification of regions affected by climate change into similar classes in terms of climate parameters is crucial for the application of consistent methods in studies conducted in these regions. Consequently, the formulation of effective strategies to mitigate the repercussions of climate change in these regions is contingent upon the accurate determination of the aforementioned strategy.The observation records evaluated within the scope of the study were obtained from 31 stations of the Turkish State Meteorological Service in the Black Sea Region, encompassing the period between 1982 and 2020, encompassing precipitation, temperature, and wind speed records.. The maximum number of clusters was determined as 5, the cluster analysis study was carried out by using fuzzy c-means and k-means methods for 2, 3, 4, and 5 cluster numbers according to these three data together form a matrix. The determination of the optimum cluster numbers was carried out by silhouette index analysis. For the data matrix where precipitation, temperature, and wind speed were evaluated together, the most appropriate classification was obtained by the k-means method by choosing the number of clusters as 4.Öğe Comparative drought analysis in Amasya and Merzifon with ZSI, PNI and NDI under transitional climatic conditions(Elsevier, 2025) Zeybekoglu, UtkuDrought is a recurring global problem characterised by multiple climatological and hydrological parameters, causing significant damage to both the natural environment and life. The onset of a drought is characterised by a meteorological drought, which is defined as a decrease in precipitation. The present study investigates the meteorological drought experienced by Amasya and Merzifon, which are located within the transition zone between the Black Sea and continental climates in T & uuml;rkiye. The drought analysis utilised the ZSI, the PNI and the NDI which is a metric employed to quantify drought. Furthermore, the temporal trends of precipitation, temperature and drought values were investigated using Mann-Kendall, Spearman's Rho and Innovative Trend Analysis. The Drought Indices (DIs) identified significant dry years in 1964-1966, 1974-1975, 1981-1982, 1984, 1986, 1989-1990, 1994, 1999, 2001-2003, 2006-2007, 2011, 2013-2015, and 2017-2021. The assessment revealed that the ZSI, the PNI and NDI performed similarly in terms of identifying drought. The trend analysis results indicate a rising trend in precipitation and temperatures. While ZSI and PNI show an increasing trend, NDI also tends to decrease due to the effect of temperature. The results of both the drought and trend analyses suggest that temperature plays a more influential role in the regional climate compared to other meteorological parameters.The findings reveal the historical development of droughts in the region and their effects on the region's environment with different drought indices. The findings herein have the potential to provide a scientific foundation for the management of local drought conditions. It is posited that by implementing preventative measures and formulating suitable strategies, the likelihood of significant drought-related problems can be substantially mitigated.Öğe Comparison of four precipitation based meteorological drought indices in the Yesilirmak Basin, Turkey(Hungarian Meteorological Service, 2023) Zeybekoglu, Utku; Hezarani, Alyar Boustani; Keskin, Asl UlkeDrought, which is often defined as not enough precipitation, does not a mean simple lack of precipitation. This condition, which occurs when humidity is less than the average value for many years, is caused by a disrupted balance between precipitation and evaporation in a region. It is very difficult to predict the start and the end time of drought. In the present study, the drought conditions of the stations selected from Yesilirmak Basin between 1970 and 2014 were determined by using Z-Score Index (ZSI), China-Z Index (CZI), Modified China-Z Index (MCZI), and Standard Precipitation Index (SPI), and the compliance of these indices to the SPI was investigated. It was determined that these indices gave parallel results to each other, and SPI detected drought earlier than other indices.Öğe Comparison of precipitation-based drought indices: Drought assessment and monitoring in a TR82 region in Türkiye(Pergamon-Elsevier Science Ltd, 2026) Zeybekoglu, UtkuDrought is a multifaceted natural hazard with profound impacts on water resources, agriculture, ecosystems, and socio-economic systems. This study investigates meteorological drought in the TR82 Region of northern T & uuml;rkiye, analysing precipitation data from ten meteorological stations spanning 1981-2023. Three precipitation-based drought indices-the Standardized Precipitation Index (SPI), China-Z Index (CZI), and Z-Score Index (ZSI)- were applied to assess drought characteristics, including frequency, severity, and spatial variability. Analysis revealed recurrent drought periods in 1981-1982, 1985-1986, 1989, 1992-1994, 1996, 2003-2004, 2006-2008, 2013, 2017, 2020, and 2022, indicating that drought occurrence in the region is neither sporadic nor isolated. Moderately dry and wet conditions were more frequent than extreme events, while prolonged droughts after 2000 suggest increasing persistence and intensification. Correlation analysis demonstrated very strong agreement among the indices, with mean correlation coefficients of 0.9956 (SPI-ZSI), 0.9953 (SPI-CZI), and 0.9943 (ZSI-CZI), confirming ZSI as a viable alternative to SPI for regional drought monitoring. In addition, the results are consistent with the presence of scale-invariant, nonlinear dynamics in precipitation variability, as indicated by observed power-law behavior and the framework of self-organized criticality (SOC) in rainfall systems, suggesting that short-term fluctuations are statistically related to longer-term patterns. The use of precipitationbased drought indices showed that the driest years align with the years of lowest annual precipitation, and similar correspondence is observed for wet years. These findings provide robust evidence of the TR82 Region's vulnerability to drought and underscore the importance of multi-index approaches and consideration of nonlinear climate dynamics for effective drought assessment and proactive water resource management.Öğe Defining rainfall intensity clusters in Turkey by using the fuzzy c-means algorithm(Univ Zagreb , Andrija Mohorovicic Geophys Inst, 2020) Zeybekoglu, Utku; Keskin, Asli UlkeTurkey has seven traditionally accepted climatic zones that are defined primarily by maritime and topographic influences. Across these zones, the annual amount of rainfall, including its intensity and its seasonal distribution, vary considerably. These variations, which impact on both urban and rural communities, including the occurrence of water shortages and flash flooding events. are increasing in both frequency and magnitude due to global warming and climate change. Several types of climate occur in Turkey where climate zones have been defined with various methodologies. To better understand rainfall intensity patterns across Turkey, this study used the Fuzzy C-Means (FCM) algorithm to define their spatial distribution. In the first stage, the annual maximum rainfall intensity records for periods ranging from 30 to 78 years were obtained from 95 stations operated by the Turkish State Meteorological Service, and the longitude, latitude and altitude data for the stations were compiled for cluster analysis. Secondly, all rainfall intensities and geographical values were normalized, and in the third stage. the FCM algorithm was applied. The comparison of annual maximum rainfall intensities revealed five clusters. Four clusters were identified as discrete zones and one was identified as a transitional zone. Weather stations located in different geographical regions sometimes fell into the same clusters. In other words, rainfall events of similar intensity can occur in different climatic zones. This study, which brought a different perspective to clustering studies, showed that rainfall intensity values can be successfully analyzed at a national scale with the FCM technique.Öğe Detrended fluctuation analyses of rainfall intensities: a case study(Inderscience Enterprises Ltd, 2020) Zeybekoglu, Utku; Keskin, Asli UlkeThe main source of the irregularity in the rainfall regimes is global climate change. These irregularities in the precipitation regime cause sudden and heavy rains, which increases the risk of flooding especially in cities. Therefore, the investigation of the change in precipitation intensities over time has great implications in terms of hydrology, water resources and urbanisation. In this study, rainfall intensity of Artvin meteorological station which is located in the Black Sea Region of Turkey is investigated. This station differs from the other stations in the Black Sea Region with extreme rainfall characteristics. Data of 14 standard duration rainfall intensity series with durations of 5 min to 24 h were used. First of all, two methods were applied for homogeneity control and then trend analysis was performed. Assuming that the factor destabilising the homogeneity is the trend, a detrended fluctuation analysis (DFA) was performed. After the implementation of DFA, homogeneity and trend analysis were reapplied to the data. In conclusion, it was determined that the main reason for the deterioration of rainfall intensity was the trend.Öğe Drought Investigation Using SPI and SPEI Methods: A Case Study in Kirikkale(Kirikkale Üniversitesi, 2022) Aktürk, Gaye; Zeybekoglu, Utku; Yildiz, OsmanDrought is one of the most important natural disasters with various social and environmental effects. Therefore, it is very important to choose a particularly suitable index for monitoring drought. Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) are widely used in drought monitoring. In this study, drought analysis was carried out using SPI and SPEI methods in order to examine the development and characteristics of drought in the city of Kirikkale, which has semi-arid characteristics. SPI and SPEI values were calculated on 1, 3, 6, 9 and 12-month time scales by using monthly precipitation and temperature data from Kirikkale meteorology station between 1963 and 2018. While calculating the potential evapotranspiration (PET) values in the SPEI calculation, Thornthwaite and Hargreaves models were used and two different SPEI values were obtained. As a result, high correlation values were obtained between all indices in the same time scale. It has been concluded that SPI and SPEI methods are applicable in the detection and monitoring of drought in the study area.Öğe Effects of Southern Oscillation and North Sea-Caspian Pattern on the rainfall intensity series in the Black Sea Region of Türkiye(Hungarian Meteorological Service, 2026) Keskin, Asli Ulke; Kazembeigi, Reza; Zeybekoglu, UtkuThis study investigates the influence of the Southern Oscillation and North Sea-Caspian Pattern on maximum rainfall intensities in the Black Sea Region of T & uuml;rkiye. Annual maximum rainfall intensity series from 16 meteorological stations were analyzed, and correlation coefficients were calculated and evaluated at . = 0.01, 0.05, and 0.10 significance levels. Results indicate that the Southern Oscillation predominantly affects short-and medium-duration rainfall in Sinop, whereas the North Sea-Caspian Pattern shows significant correlations with medium-and long-duration rainfall in Bart & Otilde;n, Bayburt, and G & uuml;m & uuml;& uacute;hane. These findings highlight the spatially varying influence of atmospheric oscillations on rainfall extremes in the region.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, UtkuIn 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.Öğe Evaluation of the relationships between atmospheric indices and rainfall intensities: Black Sea region Türkiye(Elsevier, 2024) Keskin, Asli Ulke; Kazembeigi, Reza; Zeybekoglu, UtkuRecent studies show that global atmospheric oscillations are effective on climate parameters. In this study, the relationship between the North Atlantic Oscillation and the Arctic Oscillation with the annual maximum rainfall intensity series throughout the Black Sea region of T & uuml;rkiye was investigated. In this context, the correlation coefficients between atmospheric oscillations and rainfall intensities were calculated. The correlations obtained were evaluated at the significance levels of alpha = 0.01, alpha = 0.05 and alpha = 0.10 according to Student t test. As a result of these evaluations; It was determined that the Arctic Oscillation was effective on rainfall intensities in & Ccedil;orum, Artvin, Rize and Bart & imath;n. In particular, significant correlations were found in all standard times in Artvin. Significant correlations were found between the North Atlantic Oscillation and the standard rainfall intensity series in & Ccedil;orum, Sinop, Artvin, Rize and Bayburt.Öğe Future changes in drought characteristics in the Central Black Sea region of Türkiye using HadGEM2-ES climate models and the SPI(Springer, 2025) Kurtoglu, Selcuk Erdem; Keskin, Asli Ulke; Zeybekoglu, UtkuThis study investigates future changes in meteorological drought characteristics in the Central Black Sea Region of T & uuml;rkiye (Tokat, & Ccedil;orum, Amasya, Ordu, and Samsun) for the period 2023-2080. Using precipitation projections from the HadGEM2-ES climate model under RCP4.5 and RCP8.5 scenarios, the Standardized Precipitation Index (SPI) was applied at 1-, 3-, 6-, and 12-month timescales. The analysis reveals a reduction in the frequency of near-normal wet conditions, alongside a noticeable increase in the frequency and severity of dry periods, particularly in the inland provinces. Although some coastal areas are projected to receive more precipitation, drought conditions are still expected to intensify, reflecting complex regional responses to climate change. The results of this study are intended to support long-term water resource management, agricultural planning, and climate adaptation efforts in the region.Öğe Hydrological and Meteorological Drought Forecasting for the Yesilirmak River Basin, Turkey(Hakan ÇAGLAR, 2021) Hezarani, Alyar Boustani; Zeybekoglu, Utku; Keskin, Asli ÜlkeDrought 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.Öğe Investigation of annual droughts of Boyabat region using different meteorological drought indices(Hakan ÇAGLAR, 2022) Zeybekoglu, Utku; Sahin, AhmetDrought, which is a natural disaster that increases its effects day by day, can cause significant damage. Several drought indices were carried out to determine drought. By means of these indices, drought can be determined and necessary precautions can be taken against drought. In this study, an annual drought survey was conducted using the rainfall records of the Boyabat meteorological observation station in the Kizilirmak River Basin in the 1976-2017. In the drought analysis, the meteorological drought indices Z-Score Index, China-Z Index and Modified China-Z Index were used. The dry and wet periods of the station were determined by means of meteorological drought indices, and the driest and wettest years were also determined. In the study, which also examined the compatibility between indices, it was determined that the coefficient of determination values of MCZI-ZSI and MCZI-CZI were higher than the ZSI-CZI. Drought events in Boyabat region should be investigated using different indices.Öğe Investigation of Applicability of Artificial Bee Colony Algorithm on Rainfall Intensity Duration Frequency Equations(Polish Soc Ecological Engineering, 2020) Zeybekoglu, Utku; Keskin, Asli UlkeThe main objective of this study was to investigate the applicability and efficiency of an artificial bee colony optimization algorithm to determine two statistical-based rainfall intensity duration frequency equations' weighting parameters. For this aim, the annual maximum rainfall records were obtained from seven meteorological stations of seven geographic regions in Turkey. It was observed that the Artificial Bee Colony algorithm, which is an alternative technique for solving the rainfall intensity duration frequency equations, gives very good results in selected seven meteorological stations.Öğe Investigation of the Performance of Metaheuristic Optimization Methods by Using a Simple Water Distribution Network(Giresun Üniversitesi, 2017) Zeybekoglu, UtkuScientific and technological developmentstogether with the effect of increasing population, the sharing and usage ofwater on the earth gains more importance from day to day. It is a necessitythat this material which is so valuable on the earth is to be saved and usedadequately. In this study, it is aimed to determine the optimum conditions ofthe water in the pipes in a simple water distribution network. For thispurpose, the solution of the sample network has been realized by using theCuckoo Search and Firefly Algorithms and examined together with the results inthe literature. It has been determined that the solution of the network usingthe Cuckoo Search Algorithm is better than the other algorithms.Öğe K-means clustering of precipitation in the Black Sea Region, Türkiye(Hungarian Meteorological Service, 2025) Keskin, Asli Ulke; Kir, Gurkan; Zeybekoglu, UtkuIn recent years, there has been a significant uptick in the frequency of disasters stemming from the impacts of global climate change. In response, both nationally and internationally, various studies are being conducted to mitigate these effects. Classifying regions affected by climate change into similar classes based on climate parameters is crucial for applying consistent methodologies in studies conducted within these regions. This approach will help determine the most appropriate strategies for mitigating the effects of climate change in these regions. The study utilized observational records of annual precipitation from 31 stations in the Black Sea Region, sourced from the Turkish State Meteorological Service, covering the data spans the period between 1982 and 2020. Cluster analysis was conducted using the k-means algorithm. The optimal cluster among those formed was determined through the silhouette index analysis. The study suggests that the optimal number of clusters is 2.Öğe Multifractal characterization of meteorological droughts in Turkiye's mediterranean region using visibility graph approaches(Springer, 2026) Simsek, Oguz; Zeybekoglu, Utku; Plocoste, Thomas; Adarsh, S.This study introduces a novel framework based on visibility graph (VG) and its upside-down variant (UDVG) to assess the multifractal structure of meteorological droughts in Turkiye's Mediterranean region. Using the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) from 24 stations (1970-2022), we examined drought dynamics across time scales ranging from 1 to 24 months. The analysis shows that except for a few one-month cases, drought indices exhibit predominantly stochastic rather than chaotic behaviour, validating the use of multifractal tools. VG and UDVG approaches were then applied to 3-, 6-and 12-month series, and multifractal spectra were computed via the sandbox and Chhabra-Jensen methods. Results indicate that SPEI consistently displays stronger multifractality than SPI, confirming the added role of evapotranspiration in drought variability. The UDVG framework reduced the multifractal spread (Delta Dq = D-0-D-2) by similar to 30% compared to VG (mean Delta Dq = 0.49 vs. 0.72), highlighting its sensitivity to low-amplitude, persistent droughts. In contrast, VG emphasises high-magnitude wet-dry fluctuations. This dual-network approach therefore provides complementary perspectives: VG is better suited to identifying extreme wet conditions, while UDVG can capture low amplitude fluctuations, which are cautionary sign leading to long term drought and its small changes can be early indicators of drought disasters. Overall, the proposed VG/UDVG-based multifractal framework provides novel insights into drought complexity and has the potential to support the development of early warning systems and adaptation strategies in Mediterranean-type climates.
