Abstract:The North Atlantic Oscillation (NAO) is a large-scale mode of natural climate variability governing the path of Atlantic mid-latitude storm tracks and precipitation regimes in the Atlantic and Mediterranean sectors. The primary focus of this study is to investigate the variability of lake levels in seven lakes scattered across Turkey using the method of continuous wavelet transforms and global spectra. The long winter (December, January, February and March) lake-level series and the NAO index (NAOI) series were subjected to wavelet transform. The global wavelet spectrum (energy spectrum of periodicities) of lake levels and winter NAOI anomalies, in most cases, revealed a significant correlation. It was shown that the Tuz, Sapanca, and Uluabat lakes reflect much stronger influences of the NAO than the other four lakes. In contrast, weak correlations were found in the coastal areas of the Mediterranean and eastern Turkey. The periodic structures of Turkish lake levels in relation to the NAO revealed a spectrum between the 1-year and 10-year scale level. Although the periodicities of more than 10-year scale levels were detected, explaining significant relations between the NAO and these long-term periodicities remains a challenging task. The results of this study are consistent with the earlier studies concerning the teleconnection between the NAO and climate variables in Turkey.

Many statistical methods have been developed and used over time to analyze historical changes in hydrological time series, given the socioeconomic consequences of the changes in the water cycle components. The classical statistical methods, however, rely on many assumptions on the time series to be examined such as the normality, temporal and spatial independency and the constancy of the data distribution over time. When the assumptions are not fulfilled by the data, test results are not reliable. One way to relax these cumbersome assumptions and credibilize the results of statistical approaches is to make a combined use of graphical and statistical methods. To this end, two graphical methods of the refined cumulative sum of the difference between exceedance and non-exceedance counts of data points (CSD) and innovative trend analyses (ITA)-change boxes alongside the classical statistical Mann–Kendall (MK) method are used to analyze historical precipitation changes at 16 stations during 1960–2015 in the Black Sea region of Turkey. The results show a good match between the results of the graphical and statistical methods. The graphical CSD and ITA methods, however, are able to identify the hidden trends in the precipitation time series that cannot be detected using the statistical MK method.

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The recently advanced approach of wavelet transforms is applied to the analysis of lake levels. The aim of this study is to investigate the variability of lake levels in four lakes in the Great Lakes region where the method of continuous wavelet transform and global spectra are used. The analysis of lake-level variations in the time-scale domain incorporates the method of continuous wavelet transform and the global spectrum. Four lake levels, Lake Erie, Lake Michigan, Lake Ontario, and Lake Superior in the Great Lakes region were selected for the analysis. Monthly lake level records at selected locations were analyzed by wavelet transform for the period 1919 to 2004. The periodic structures of the Great Lakes levels revealed a spectrum between the 1-year and 43-year scale level. It is found that major lake levels periodicities are generally the annual cycle. Lake Michigan levels show different periodicities from Lake Erie and Lake Superior and Lake Ontario levels. Lake Michigan showed generally long-term (more than 10 years) periodicities. It was shown that the Michigan Lake shows much stronger influences of inter-annual atmospheric variability than the other three lakes. The other result was that some interesting correlations between global spectrums of the lake levels from the same climatic region were found.

Altyapı sistemleri, kentsel sistemin temel öğelerindendir. Elektrik, su, doğalgaz ve internet gibi temel ihtiyaçların kesintisiz sağlanabilmesi, kullanım sonucu açığa çıkan atık suların güvenli bir şekilde uzaklaştırılabilmesi için altyapı sistemlerinin gelişen kent hayatına cevap verebilecek nitelikte ve sürdürülebilir olması gerekmektedir. Kırsal alanlardan kentlere doğru olan göçler sonucu artan kent nüfusu, altyapı sistemlerinin önemini arttırmaktadır. Yeni hatlarının yapımı, var olan hatların bakım ve onarımı özellikle yoğun nüfuslu kentlerde önem kazanan bir konu haline gelmektedir. Söz konusu işlemler açık kazı yöntemiyle yapılabileceği gibi, sosyal ve ekonomik maliyetlerin yüksek olmasından dolayı kazısız yöntemler son yıllarda tercih edilmektedir. Özellikle hızla gelişen teknolojiler ile birlikte kazısız yöntemler, geleneksel açık kazı yöntemlerine göre teknik, ekonomik ve sosyal açılardan daha uygulanabilir olmaktadır.