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ÖgeFizik tabanlı tam yayılı hidrolojik modellerin kalibrasyonunda uydu tabanlı verilerin kullanılması(Lisansüstü Eğitim Enstitüsü, 2023-01-31)Hidrolojik model parametreleri geleneksel yaklaşımda havza çıkışında gözlenen günlük nehir akım verileriyle tahmin edilmeye çalışılır. Modern yaklaşımda ise akım verileri yanında herkese açık uydu tabanlı uzaktan algılama verilerinden de azami istifade edilmeye çalışılır. Uzaktan algılama verilerinin kullanıldığı yöntem ile ulaşılan alansal model çıktıları, sadece akım verisiyle elde edilen noktasal iyileştirme sonuçlarına göre daha tutarlı ve güvenilirdir. Bu nedenle fizik tabanlı sonlu elemanlar yöntemiyle çalışan matematiksel havza modellerinin uydu verileriyle kalibrasyonu dünyada giderek yaygınlaşmaktadır. Bu çalışmamızın amacı uzaktan algılama yöntemleriyle elde edilmiş buharlaşma ve terleme verilerinin hidrolojik model kalibrasyonuna etkilerini araştırmaktır. Bunun için veri kalitesi yüksek Fransa'nın Vienne havzasında fizik tabanlı tam yayılı mHM modeli kurulmuş ve 11 senaryolu kalibrasyon deneyleri yapılmıştır. 2002-2014 kalibrasyon dönemindeki modelin akım benzeşim performansı modelin günlük akım çıktıları ile gözlenen akım değerleri arasında hesaplanan KGE, modelin alana yayılı fiziksel performansı ise mHM'in uzun dönem (2002-2014) aylık buharlaşma ve terleme (AET) raster çıktı haritaları ile referans MODIS-AET raster haritaları arasında üçer aylık üç dönemde (1. dönem: Mart, Nisan, Mayıs, 2. dönem: Haziran, Temmuz, Ağustos 3. dönem: Eylül, Ekim, Kasım için) hesaplanan SPAEF değerleri ile ortaya konmuştur. 1998-2001 arası 4 yıl ön koşturma (spin-up) dönemi olduğundan performans hesaplarına dahil edilmemiştir. Model parametreleri Ostrich yazılımı içerisinde bulunan 750 iterasyonlu paralel pareto-DDS (PARA-PADDS) yöntemi kullanarak kalibre edilmiştir. Sonuçlara göre, sadece havza çıkışında konumlandırılan bir tek akım gözlem istasyonundan elde edilen akım verilerinin kullanıldığı kalibrasyonda (senaryo 1) modelin akım performansı beklendiği gibi çok yüksek (KGE 0.91, maksimum değeri 1); modelin AET performansı ise üç dönemde de çok düşüktür (SPAEF -0.16, -0.21, -0.26). Havza çıkışındaki AGİ ve nehrin farklı alt kollarında konuşlu 3 AGİ'den alınan akım verileriyle 4 AGİ'li kalibrasyonda (senaryo 2) ortalama KGE 0.91'den 0.37'ye düşerken ve üç dönemin SPAEF değerleri -0.72, 0.76, 0.55 olmuştur. Tek AGİ ve uydu verili kalibrasyonda (senaryo 3) akım performansında 0.91'den düşme çok sınırlı olmuş (KGE 0.90), bunun yanında AET performansı üç dönemde de önemli oranda iyileşmiştir (SPAEF 0.64, 0.77, 0.74). Akım ölçümü hiç olmayan sadece uydu verili kalibrasyonda (4. senaryo) su dengesi sağlanamamış (KGE -0.24), üç dönemde SPAEF 0.39, 0.69, 0.67 değerlerini almıştır. Veri eksikliği yaşanan havzalar için iki senaryo (5 ve 6) kurgulanmıştır. Bir yılda ve sadece her ayın ortasında tek ölçüm, toplamda 12 adet akım verisi ve MODIS-AET uydu verisiyle kalibrasyonda (senaryo 5) su dengesi ve AET performansının iyileştiği gözlemlenmiştir (KGE 0.67 ve üç dönemde SPAEF 0.65, 0.82, 0.76). MODIS-AET yanında sadece bir yıllık günlük akım verileri kullanılan 6. senaryoda KGE 0.72 ve üç dönemde SPAEF 0.64, 0.80, 0,79 değerlerini almıştır. Kurgulanan diğer 5 farklı senaryoda karasal gözlemler yerine global akış verilerinden elde edilen zaman serileri kullanılmıştır. Bu diğerlerinden farklı 5 senaryoda bilhassa hiçbir ölçüm verisinin olmadığı havzalarda çok amaçlı çoklu kalibrasyon yaklaşımının karasal gözlemlerden tamamen bağımsız olarak yürütülüp yürütülemeyeceği sorusuna cevap aranmıştır. ERA5_LAND ve GLDAS akış verilerinin kullanıldığı senaryolarda uydu verisi MODIS-AET kullanılmıştır. Bu senaryolar içinde S11`de GLDAS ve MODIS-AET aylık ortalamalar ile yapılan çok amaçlı çoklu kalibrasyonda su dengesi önemli ölçüde sağlanmıştır. Bu senaryo kurgusunda diğerlerinde olduğu gibi karasal gözlemlerin bulunmadığı kabulünden yola çıkarak akış verisi ve AET verisi ücretsiz olarak uydu ve uydu bazlı yeniden analiz ürünü olarak temin edilmiştir. GLDAS global yeniden analiz ürünü yayılı akış verileri uzun yıllar ortalması 12 aylık zaman serilerine dönüştürülerek MODIS`den alınan yayılı AET verileri ile birlikte kalibrasyonda kullanılmıştır. KGE değerinin 0,37`ye çıkmasına rağmen SPAEF değerlerinin sırası ile 0,63; 0,78 ve 0,75 değerlerini alması diğerleri ile kıyaslandığında su dengesini önemli ölçüde sağlamıştır. S7 senaryosunda 2002-2014 yılları arası ERA5_LAND akış verisinin zaman serileri kullanılırken MODIS AET verileri patern yönünden hedeflenmiştir. Bu kurguda KGE değerleri sıfıra yakın çok küçük değerler alırken SPAEF okumaları HTA ve EEK dönemlerinde yüksek okumalar vermiştir. Fakat su dengesi sağlanamamıştır. S8 kurgusunda ERA5_LAND için 2002-2014 arası uzun dönem aylık veriler kalibrasyonda kullanılmıştır. MODIS AET veriside çok amaçlı çoklu kalibrasyonun diğer amaç fonksiyonuna konu edilen alansal girdisi olmuştur. Bu kurguda SPAEF değerlerinin yüksek değerler alması (0,64; 0,78; 0,73) yanında KGE okumaları sınırlı bir iyileşme göstermiştir (0,18). Her ne kadar havzanın fiziki temsili iyileşmiş olsada su dengesi sınırlı kalmıştır. 9 numaralı senaryoda akış verisi uzun yılların ortalaması alınarak aylık toplamlar şeklinde akış serilerine sokulurken kalibrasyon için bir diğer girdi yine MODIS AET olmuştur. Bu kurguda SPAEF değerleri önemli ölçüde yükselme gösterirken (0,63; 0,77; 0,80) KGE değeri eksi değerler alarak (-0,18) su dengesinden uzaklaşılmıştır. S10 için yapılan kurguda hatanın amaçlandığı akış serileri ve patern yönünden amaçlanan AET verileri ERA5_LAND ürünü olarak temin edilmiş ve kalibrasyonda başka bir veri kullanılmamıştır. ERA5_LAND akış ve AET verileri uzun yıllar aylık ortalamalar şeklinde kalibrasyonda kullanılmıştır. Bu kalibrasyon neticesinde elde edilen debi ve AET simülasyonlarına ait benzeşim başarısı KGE için -0,23 değerini alırken SPAEF değerleri sırası ile 0,02; 0,29 ve 0,37 değerlerini almıştır. Su dengesinin en fazla bozulduğu ve performansı en düşük olan senaryo kurgusu burada ortaya çıkmıştır. Global ürünlerle yapılan kalibrasyonda en iyi performansı S11 senaryosu sağlarken en kötüsünü S10 sağlamıştır. Sonuçlarımız akım ölçümleri eksik ve yetersiz havzalar için ümit vericidir. Bu çalışma, fizik tabanlı modellerin uydu verileri ve uygun amaç fonksiyonları ile kalibre edildiklerinde havzanın fiziğiyle uyumlu, su dengesini de bozmayan optimum parametre setine ulaşılabildiğini göstermiştir. Bir diğer önemli çıktı ise karasal gözlemlerin hiç olmadığı bir havzada dahi ücretsiz uydu verileri ve global ürünler kullanılarak kalibrasyon başarısı sağlanabilmektedir.
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ÖgeAssessing the performance of gridded precipitation products – a comparative analysis of the Black Sea and East Africa regions(Graduate School, 2022-11-04)Hydrological and climatological studies require a good quality of precipitation data. It is difficult to assess the spatial and temporal variability of precipitation for a basin without sufficient gauging stations. Recently, several high-resolution public-domain reanalysis and gridded precipitation products (GPPs) have been produced. The performance of four GPPs in estimating the spatio-temporal distribution of precipitation was examined in this study. The chosen regions are the Rize province (Black Sea region) and the Blue Nile basin (East Africa region). Both basins have similar topograpy and high precipitation. In this study, the observed precipitation data were compared with the GPP datasets using statistical metrics and time-series plots. Then, the performance of these products was evaluated by assessing their capacity in estimating river flow with a calibrated physically based hydrological model- SWAT. On top of that, we have assessed the performance of the multi gauge calibration (MGC) technique to improve the SWAT model efficiency. We assessed four calibration methods to improve the model simulation outcome. The temporal and seasonal data performance of the GPPs was, then, assessed before testing the quality of prediction with various statistical analysis metrics. Finally, the climate change impact on the hydroclimatology of both basins was studied using GCM scenario for future climate predictions. Estimating the parameters that represent the various hydrological processes is one of the main issue hydrologists need to solve since it is impossible to measure all the hydrological parameters. We tested four methods where calibration was done using flow data: only from upstream area (US), only from downstream area (DC), using both upstream and downstream areas of the basin (MGC), and using first the upstream then downstream flow data (UCDC). The results showed that model calibration using the MGC and UCDC techniques proved to have improved the model performance, unlike the single gauge calibrations. The reason is the model obtains much wider information on the basin characteristics to adjust its parameters when more than one gauging station is used simultaneously for calibration. Our study has contributed to the validation of gridded precipitation products for the mountainous regions of the Black Sea and East Africa regions which have scarcity in weather gauging station. In addition to statistical and visual map assessment, we adopted a hydrological model (SWAT) parameterized for these basins to make original assessments on the hydrological responses for each GPP dataset precipitation inputs. The resulting graph showed that the annual cyclic behavior of all data is quite consistent with each other, like having a peak on May. The result for the Ikizdere basin indicated that the peak water yield magnitude estimattion in May is significantly greater than the observed water yield for CFSR and MSWEP datasets. However, the water yield value was lower for APHRODITE. Moreover, water yields were highly overestimated during the periods May-December by the MSWEP simulation, which is due to overestimated precipitation in the first four months (January-April) when most of the precipitation falls in the form of snow. The most comparable simulated flow regime with the observation was that of the ECMWF simulation flow. When we come to the Blue Nile basin, it is considered the most important river basin for the Nile River as it generated much of the annual flow. Hence, having a good accuracy of summer precipitation (rainfall) estimate is essential for Blue Nile basin since much of the annual rainfall falls in the highland region during the summer season (Jun – Sep). The MSWEP precipitation dataset has overestimated the peak flows which is obviously caused by the overestimation of rainfall in the summer season (Jun-Sep). The CFSR dataset performance was poor with negative deviations specifically for the wet season of the year (Jun-Sep). It resulted in underestimation of flow, especially for the peak flows which could be explained by the underestimation of precipitation over the study area. Among the GPPs, ECMWF captures the annual cycle of the measured flow cycle with little deviations. Like the Ikizdere basin, it has proved to perform better for the Blue Nile basin, where both the total water yield and surface flows for the wet has been estimated with good accuracy. The results allign with the previous studies outcomes which concluded that the ECMWF weather data could not only be successfully used in place of surface weather observation records, but also improve hydrological modelling performance. For both study areas, the ECMWF gridded precipitation estimates have been proven to be the most comparable with the observed precipitation suggesting that the dataset could be implimented for mountaneous areas of the world with very scarce ground weather observation stations. Finally, the seasonal average simulated flow of Ikizdere basin was forced with the GCM climate change scenarios and compared with the observed flow at basin outlet. There is consist trend in the forecasted flow for the various GCM projections. There is a dipole of climate projection underperformance in the sense of underestimation for winter & autumn seasons, whereas, overestimating for the spring season. For winter (Dec – Feb) and autumn (Sep-Nov), all the climate models forecast decrease in flow for the river, whereas for the spring season (Mar-May) all the GCMs forecasted an increase in flow. Hence, towards the end of the century, the climate projections indicate a decreasing trend for the winter season and an increasing trend for spring season. This finding agrees with the previous study results where the long-term historical precipitation data analysis demonstrated a decreasing trend in winter season for the Black Sea region. The case is difference for summer season where the GCM scenarios didn't agree on the precipitation projection trend. Generally, the impact of climate change on the seasonal precipitation of the Rize province project a decreasing trend for the winter season and increasing trend for spring season towards the end of the century. When we come to the Blue Nile basin, the GCM scenarios did not agree on the future climate projections. An increase in precipitation as well as river flow from Rosieres is projected by some of the emission scenarios (MIMR and INCM3) throughout the year except in March and April, which increases outflow in the river. Contrary to that, the other scenarios (BCM2 and CSMK3) estimate a decrease in precipitation and outflow. When we have a closer look into the emission scenarios, the A1B scenarios generally predict increased river flow for the Blue Nile river, while B1 predicts decrease in flow. A low flow, especially in summer (Jul-Sep) mean significant reduction in the heads of reservoirs in Ethiopia, Sudan and Egypt which will have a severe impact on the livelihood of people.
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ÖgeHysterical effects in flow characteristics in the wake region of group of cylinders during the passage of gradually varying unsteady flow(Graduate School, 2022-09-06)In recent studies, it has been witnessed that a group of cylinders offer some distinct advantages compared to mono-pile when applied as a support structure in marine and riverine environments. It is well established that an array of cylinders presents a viable option to a single solid cylinder with lower cost, lower scour and contraction effects. Donghai Bridge offshore wind farm in China is a practical real-world example where this type of structures are of significant importance as an offshore wind turbine support structure. In the pertinent literature, an overwhelming majority of flow-body interaction investigations are studied under steady flow conditions. Furthermore, researchers mainly focus on oscillatory flow when dealing with unsteady flow and using steady state approximation for gradually varying unsteady flows. Yet, several flow conditions observed in nature such as tsunamis, meteorology driven flows, tidal currents and river hydrographs fall into the category of gradually varying unsteady flow. In this thesis, the influence of gradually varying unsteady flow around a group of cylinders (Hexagonal arrays of Circular Cylinders, HACCs) was investigated by flume experiments. The experiments are carried out in a rectangular flume with dimension 30 m in length, 1 m in width and 1.25 in depth. The bed was smooth concrete and the sides were plexiglass walls. A honey-comb pattern was used at the inlet to ensure smooth inlet conditions. The water was recirculated through a monobloc pump and the water depth was kept constant at 30 cm through entire experiments. The flow discharge is controlled via an inverter system. By entering the desired input through the pump's control unit, unsteady and steady flow conditions are repeatedly and reliably produced. Two unsteady flow cases generated with same minimum and maximum velocities, but different durations in order to investigate the effect of unsteadiness degree. The flow velocity started at 0.04 m/s and increased to a peak of 0.23 m/s. One steady case had the duration of 90 seconds, the other had 120 seconds. Same experiments also carried out under steady flow conditions for benchmarking purposes. Velocity and water depth measurements were taken with a frequency of 100 Hz. Two resistance type level meters are used, one located 2.5 meters upstream the other downstream with the same distance. Instantaneous recording of water depth and water surface are carried out. Simultaneously, velocity measurements are collected with the help of an Acoustic Doppler Velocimeter. Velocity measurements are taken at both horizontal and vertical planes. In total, 290 measurement points were utilized, 140 points at horizontal plan and 150 points at vertical plan. The resolution of the measurement grid is increased near the obstacle in order to capture turbulence characteristics. The obstacle, HACC, consisted of 7 circular cylinders with a diameter of 3.4 cm. The circumambient diameter of the HACC was 16 cm and the solid volume fraction was 0.32. The HACC placed 12 m from the inlet to ensure fully developed flow conditions. Two arrangements of HACC, namely staggered and regular arrangement, in order to investigate the effect of obstacle orientation. In brief, three flow cases (steady, unsteady 90 seconds, unsteady 120 cases) and two HACC configurations are used. In total, 6 experimental runs are performed. Each experimental run consisted of 290 velocity measurement points. The analysis of collected data is started with the despiking of the raw data. The spikes in the velocity measurements are removed with a method widely used in the literature. Then the synchronization procedure is carried out. Velocity and water depth measurements are synchronized through their computer time recording. 290 velocity measurements that are recorded at different times are synchronized by the help of water surface slope measurements. Since water depth measurements are kept constant through all experiments, they are used as a benchmarking point. Finally, turbulence decomposition is done, turbulent and mean flow recordings are obtained to carry out post-processing. Experimental findings resulted in several significant conclusions. It is found that velocity deficit between wake and contraction region exhibits a hysterical character between rising and falling stages. The negative water surface slope is observed during the falling stage of the unsteady flow. This adverse pressure gradient causes earlier boundary layer separation and broader wake region. This leads to a stark shear layer rear the obstacle and higher lateral momentum transfer. During the passage of unsteady flow, counter-clockwise hysteresis is observed between depth-averaged velocity and turbulence kinetic energy. This means that for a given velocity, the falling stage produces higher turbulence compared to the rising stage. This effect was observable irrespective of the HACC arrangement. Furthermore, it was also observed that this hysterical relationship becomes more evident further downstream. The arrangement of HACC is also observed to be of importance in terms of hysteresis. It is observed that hysterical loops are less dramatic for the regular HACC. The hysteresis is mitigated by the strong bleed jets that occur in the wake region of regular HACC. It is known that due to the particular geometry of regular HACC, a significant amount of flow can go through the obstacle and create bleed flow which highly influences wake characteristics in terms of stabilizing the wake and controlling mixing process. It was concluded that the amplified bleed jets are the primary reason behind the suppressed hysterical behaviour. Another critical point that is outlined is the effect of unsteadiness on pile behaviour in terms of flow-body interaction. The pile is observed to render the pile to behave in a more streamlined manner. For a given velocity, the unsteady cases produced smaller recirculation compared to the steady case. The recirculation zone is also observed to be larger during the falling stage compared to the rising stage. Yet, this effect also seems to be less pronounced for the regular arrangement of HACC. The strong bleed jets are presumed to weaken this behaviour.
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ÖgeSu dağıtım şebekelerinde en uygun basınç yönetimi metodunun belirlenmesi(Lisansüstü Eğitim Enstitüsü, 2022-09-15)Su dağıtım şebekelerinde meydana gelen yüksek basınçlar, hem su kayıplarını, hem de boru arızalarının meydana gelme sıklığını arttırmaktadır. Su kayıplarını ve boru arızalarının miktarını azaltmak, ve su dağıtım şebekelerinin faydalı ömrünü uzatmak için yüksek olan basıncı düşürmek gerekmektedir. Fakat şebekeden su alan tüketicilerin tamamının basınçlı su kaynağından istifade edebilmesi için basıncın şebekede izin verilen minimum değerden daha düşük olmaması gerekmektedir. Bu sebeple basıncın hassas bir şekilde yönetilip su kayıpları ve boru arızalarının azaltılması, ve abonelerin suya erişiminin aksamaması önemlidir. Pratikte dört farklı basınç yönetimi metodunun var olduğu bilinmektedir. Bunlar Sabit Çıkışlı, Zaman Ayarlı, Debi Ayarlı ve Kritik Nokta Ayarlı Basınç Yönetimi metodlarıdır. Sabit Çıkışlı Basınç Yönetimi'nde şebekenin girişindeki PRV'nin (Pressure Reducing Valve = Basınç Düşürücü Vana) sabit bir çıkış basıncı vardır ve bu basıncın değeri zamana veya debiye göre değişmez. Zaman Ayarlı Basınç Yönetimi tatbik edilirken PRV çıkışında, gece saatlerinde gündüz saatlerine göre daha düşük çıkış basıncı verilmektedir. Böylece su tüketiminin az ve basıncın yüksek olduğu gece saatlerinde meydana gelen su kayıpları azaltılmış olur. Debi Ayarlı Basınç Yönetimi'nde PRV'nin çıkış basıncı, PRV'den geçen debiye göre sürekli güncellenir. Bu yöntemde debi arttığında çıkış basıncı artar, debi azaldığında da PRV'de yük kaybı arttırılır ve böylece çıkış basıncı azalır. Kritik Nokta Ayarlı Basınç Yönetimi'nde ise su dağıtım şebekesindeki kritik nokta basıncının şebekede izin verilen minimum değerde sabit tutulması hedeflenir. Burada kritik nokta, şebekedeki en düşük basınçların meydana geldiği noktadır. Bir su dağıtım şebekesinde en uygun basınç yönetimi metodunun belirlenebilmesi için hidrolik olarak modellenmesi gerekmektedir. Dört farklı basınç yönetiminin hidrolik olarak modellenmesi EPANET 3 adlı açık kaynak kodlu yazılımda gerçekleştirilmiştir. EPANET 3'ün mevcut versiyonu hidrolik çözücü olarak yarı-kararlı akımların hidroliğini esas alan Küresel Gradyan Algoritması'nı (GGA) kullanmaktadır. Bu çalışma kapsamında basınç yönetimi yapılırken ise sıkıştırılamaz değişken akımların hidroliğini esas alan Rijit Su Sütunu Küresel Gradyan Algoritması (RWC-GGA) kullanılmıştır. Büyüklüğü, tüketim paterni ve su kaybı miktarı farklı olan 18 su dağıtım şebekesi üzerinde yapılan basınç yönetimi hidrolik simülasyonları sonucunda hangi basınç yönetimi metodunun hangi tip şebekede ve hangi birim su maliyetinde en uygulanabilir olduğu belirlenmiştir. Bu analizlere göre birim su maliyetinin yüksek olduğu durumlarda Kritik Nokta Ayarlı, düşük olduğu durumlarda da Sabit Çıkışlı veya Zaman Ayarlı Basınç Yönetimi metodlarının malî açıdan en avantajlı seçenekler olduğu anlaşılmıştır.
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ÖgeComprehensive flood risk assessment and identification of the potential flood mitigation strategies(Graduate School, 2022-06-09)Floods are among the natural disasters frequently encountered in our country, i.e. Turkey, and across the globe. Considering some of the conditioning factors, such as geographical location, geological and hydrological structure and even demographic characteristics, that characterize the formation of natural disasters, the most common natural disasters in Turkey are described as floods. A total of 1209 floods occurred in Turkey between 1975 and 2015, resulting in 720 deaths and the inundation of 900,000 hectares. In addition, floods cause an annual average of 100 million dollars of economic loss. The constitution of floods may vary in different types; scuh that coastal floods are frequent in coastal areas, while river floods mostly occur in rural and/or urban areas, and urban flooding poses significant challenges in densely populated regions. In this context, especially in cities with high population densities, urban flood events not only cost human lives but also cause serious property damage. Istanbul is also among the cities that frequently face urban floods across Turkey. The city is the most populated city in Turkey with a population of approximately 16 million (2986 people/km²) and is at serious risk of flooding. Therefore, within the scope of this thesis, it is aimed to determine the regions that may be affected as a result of the floods potentially occur in Istanbul and to reveal the factors that trigger the vulnerability of these regions. In order to ensure the functionality of both data collection procedures and the early diagnosis actions to be determined on an administrative basis, analyzes were carried out on a district basis in this thesis. Through district-based analyzes, both hazard and vulnerability factors, which are the two most critical pillars of the risk concept, were carried taken into account. In line with the hazard cluster, stormwater pipe network, slope, imperviousness (in terms of curve number), number of rainy days and return period of storm event criteria were taken into the consideration. Within the scope of vulnerability cluster, vulnerable structures, population density, vulnerable population, education level, income level, transportation network, number of households and land use criteria were considered. Thus, this thesis not only tried to determine the regions having high susceptibility of flooding but also sought to designate the social environments, i.e., residents and/or buildings, that have the potential to be damaged as a result of floods. In the research articles included in this thesis, multi-criteria decision-making algorithms were used to perform the district-based flood risk mapping of Istanbul. In the first research article published within the scope of the thesis, district-based flood risk maps were generated using the fuzzy analytic hierarchy process, and risky districts and the criteria to be taken into account specific to these districts were identified. In the second research article published within the scope of the thesis, the perception differences on the flood risk of four different stakeholders (i.e., Istanbul Water and Sewerage Administration, Disaster Coordination Center, Istanbul Metropolitan Municipality and Universities) at Istanbul scale were analyzed. For these purpose, the technique for order of preference by the similarity-to-ideal-solution (TOPSIS) method was integrated along with the fuzzy analytical hierarchy process method utilized in the first study. As a result of the model configurations on the basis of expert judgments pertaining to abovementioned four institutions, flood risk, flood hazard and flood vulnerability maps were separately generated. The third research article published within the scope of the thesis focused on the interrelationships of the criteria that were not examined in the previous two studies. On the other hand, for the first time in the literature, analyzes were carried out using two distintictive criteria weighting methods (analytical hierarchy process for the hazard cluster and analytical network process for the vulnerability cluster) together. At this point, another innovation that has been methodically accomplished is the integration of the decision-making trial and evaluation laboratory (DEMATEL) method which was used in the refinement of the analytical network process framework. Visekriterijumska optimizacija i compromisno resenje (VIKOR) method, which is accepted as an improved version of the TOPSIS method, was performed to prioritize the districts in terms of flood risk by combining the outputs obtained from the two different criteria weighting methods and the numerical values of the corresponding criteria. According to the findings obtained in the first of the articles published within the scope of the thesis, land use, population density and the vulnerable structures were determined as the most important vulnerability criteria, while the return period of a storm event, imperviousness and stormwater pipe networks were obtained as the most significant hazard criteria. On the other hand, the comparison between the main clusters, i.e., vulnerability and hazard, indicates that these two classes have almost equal importance in terms of the flood risk concept in Istanbul. In addition, sensitivity analyzes were implemented in order to illustrate the stability and robustness of the fuzzy analytic hierarchy process applications. According to the district-based analyzes, Bayrampasa, Bagcilar and Esenler were found to be the three most risky districts with the significant effect of their dense populations. While Uskudar, Bayrampasa and Bagcilar districts stand out according to the hazard cluster representing the probability of flood events, it was concluded that special precautions should be taken for Gaziosmanpasa, Gungoren and Beyoglu districts according to the analyzes made within the generic of vulnerability cluster. According to the findings obtained in the second of the articles published within the scope of the thesis, disaster management and coordination authorities and local municipalities have point out that hazard and vulnerability clusters have almost similar importance in terms of flood risk. On the other hand, water and sewerage administrations take the hazard class into consideration, while universities consider vulnerability more important than the other. Once the produced flood risk maps and correlation analyzes are examined, one can conclude that there are high perception differences between the judgments of the experts from universities and water and sewerage administration, while perception similarities can be seen among other stakeholders. Therefore, this study highlighted that the inclusion of only one type of stakeholder in the flood risk management system is not sufficient to evaluate the overall flood risk criteria. Instead, it was concluded that the participation of various stakeholders from different disciplines is required to make more reliable flood risk analyzes. Hence, the results of this study not only provide a flood risk maps showing the most flood-prone districts of Istanbul, but also reveal the perception differences among various stakeholders who are responsible for taking the necessary measures to reduce, prevent and manage the flood risk. According to the findings obtained in the third of the articles published within the scope of the thesis, the income level, which is one of the criteria evaluated in the vulnerability class, not only affects all the vulnerability criteria, but also has been affected by the others (vulnerable structures, population density, vulnerable population, and education level). In addition, although the education level criterion affects all other criteria, it is only affected by the income level. Also, the population density criterion is almost as important as the education level according to the results of the study. The insight gained from the DEMATEL analysis has indicated that the population density is highly correlated with the education level and income level. Furthermore, the analyzes performed for the hazard cluster showed that the return period of a storm event is the most important criterion. Hence, especially considering extreme rainfall events where climate change has a great impact, district management authorities should take special measures such as flood-retardant structures and rainwater harvesting on their agenda to deal with the floods. In addition, storm water pipe networks and imperviousness criteria, which are among the other hazard related criteria, have been found to have very close importance to each other. At this point, the fact that districts with old or insufficient storm water drainage systems focus on these investments, increase the amount of green areas in districts where the land use includes urbanization intensively, or implement sustainable measures such as green roofs on existing buildings will make significant contributions to reducing the flood risk in the relevant regions and/or districts. In general, within the scope of this thesis, comprehensive flood risk analyzes were carried out for Istanbul. In addition, not only flood risk mapping, but also the ways to be followed for strategies to reduce the flood risk in risky areas are pointed out. In this context, it is believed that the publications contained in this thesis will be useful for not only Istanbul but also entire country and will play a guiding role in taking the necessary actions.