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    Öğe
    Investigation of extreme precipitation indices in Turkey
    (Springer Wien, 2022) Acar, Zahide; Gonencgil, Barbaros
    This paper focuses on spatiotemporal characteristics of precipitation indices of Turkey's precipitation data for the periods 1966-2014. Seven precipitation indices include the number of extremely wet days, very wet days, heavy precipitation days (10 mm and 20 mm), simple daily intensity days, and consecutive dry and wet days. The indices are based on homogenized precipitation data. Besides, long-term changes and trends in the time series of precipitation indices in terms of climatic variability were investigated using nonparametric time series analysis methods. The results obtained are summarized as follows. Extremely wet and very wet day indices include significant decreasing trends in most stations. The trend is statistically significant at some stations in the Mediterranean region and southeastern Anatolia region. The number of heavy precipitation day indices tend to decrease in most of the stations in the Mediterranean precipitation zone, throughout Turkey. Simple daily intensity index generally displays an increasing trend. Consecutive dry days include an overall upward trend throughout Turkey. The inner and in the west of southeastern Anatolia regions have displayed a statistically significant increasing trend. Consecutive humid days tend to decrease overall outside of Turkey's internal parts. The study also examined the relationships between atmospheric oscillation indices and precipitation indices. Accordingly, the atmospheric oscillation index that has the most decisive effect on the Turkish precipitation indices is NAO.
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    Öğe
    Long-Term Changes in Hot and Cold Extremes in Turkey
    (Istanbul Univ, Fac Letters, Dept Geography, 2018) Acar, Zahide; Gonencgil, Barbaros; Korucu Gumusoglu, Nebile
    Extreme weathers are the leading cause of weather-related disasters all over the world. Many people lose their lives each year due to the triggering effect of cold or hot weather. The extreme days are generally defined as a period of several days of abnormally cold or hot weather. Increased frequency of these days could lead to death and disasters. This study analyzes the variability of minimum and maximum temperature defined anomalous temperature events. Daily minimum and maximum air temperature data from 156 weather stations in Turkey are analyzed to determine percentile threshold values (99th, 95th and 1st, 5th) at each station. Two statistical tests are applied to analyze trend in extreme values, namely Mann-Kendall trend analysis and cluster analysis. The Mann-.Kendall analysis demonstrates an increase in frequency of hot and extremely hot days, whereas cold and extremely cold days show a decreasing trend in Turkey. The extreme cold days have been the highest of the year 1972, 1983, 1992 and 1993, respectively. After 2005, extreme cold days begin to decrease. The frequency of extreme hot day has increased since 2000. Especially in 2010, it has been the warmest year in Turkey from the records of the stations during the study period.
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    OBSERVED VARIABILITY STANDARDIZED PRECIPITATION INDEX IN TURKEY
    (Stef92 Technology Ltd, 2016) Deniz, Zahide Acar; Deniz, Ozan; Gonencgil, Barbaros
    Drought is a natural hazard that is derived from defective precipitations. If precipitation is not sufficient during a longer period, scarcity of water and drought can be risk for living and human activities. Standardized Precipitation Index (Standardized Precipitation index (SPI)) commonly is used for the evaluation of drought frequency and severity. SPI is mainly from rainfall within the time period established by dividing the standard deviation of the mean of the difference is obtained. This technique is used an analysis of precipitation data. SPI, usually 1, 3, 6, 9 and 12-month precipitation totals by comparing the degree of moisture is based on statistical techniques. In this study, precipitation data is provided by the Turkish State Meteorological Service. SPI variability is investigated at 156 meteorological stations in Turkey. During the years of 1971, 1972, 1986, 2000 and 2003 have experienced moderate and severe extreme drought conditions. 1966, 1967, 1975, 1998 and 2010 years have experienced extreme and moderate wet conditions.
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    Öğe
    Trends of summer daily maximum temperature extremes in Turkey
    (Taylor & Francis Ltd, 2015) Deniz, Zahide Acar; Gonencgil, Barbaros
    This work seeks to understand the variability of warm and cool events during summer in Turkey. Daily maximum air temperature data from 97 weather stations were analyzed to determine percentile threshold values (99th, 95th, 90th, 1st, 5th, and 10th) at each station. Trends in the percentile values were determined using the Mann-Kendall trend test. The analysis demonstrates an increase in frequency of warm, hot, and extremely hot days, whereas cool, cold, and extremely cold days show a decreasing trend. Increasing trends are statistically significant at the 0.05 and 0.01 levels for 13 and 46% of the stations, respectively. Significant decreasing trends have been detected at 0.05 and 0.01 levels for 19 and 15% of 97 stations, respectively. Analysis of the observations shows that the number of warm and hot event started to increase in the 1970s. Warm events are comparatively more numerous than cold events in western and southern parts of the country.
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    Öğe
    Variations in Temperature Extremes in Turkey
    (Istanbul Univ, Fac Letters, Dept Geography, 2017) Acar-Deniz, Zahide; Gonencgil, Barbaros
    The study area is located between 36 degrees to 42 degrees N and 26 degrees to 45 degrees E. In this study, we have used the data that has been provided by the Turkish State Meteorological Service (TSMS), including the daily minimum, maximum, and average temperatures that were recorded at 156 meteorological stations. Daily data are converted into monthly and seasonal data to explain the descriptive statistics during winter and summer. Datasets that are used to determine temperature extremities comprise daily and original data. This study aims to understand the spatial and temporal distribution patterns of extreme summer and winter temperatures in Turkey. The Kruskal- Wallis (K-W) test is performed to determine whether any significant changes in the temperature data are observed. The Mann-Kendall (M-K) order correlation coefficient method is performed to understand the nature and magnitude of the variability in data. According to K-W test statistics, a statistically significant inhomogeneity is observed, particularly during summer at all stations at most of the temperatures. Furthermore, according to the M-K test statistics, a statistically significant increase in temperature extremes (i.e., during summer days, tropical nights, and extreme temperature range) is observed throughout Turkey.