LEE- Yer Sistem Bilimi Lisansüstü Programı

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http://hdl.handle.net/11527/19499

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Konu "iklim değişikliği" ile LEE- Yer Sistem Bilimi Lisansüstü Programı'a göz atma
  • Öge
    Analysis of global climate change on the hydrography of the Black Sea using CMIP6 climate models
    (Graduate School, 2023-01-06) Çetin, Derin Ülger ; Ilıcak, Mehmet ; 601191004 ; Earth System Science
    Climate change has numerous impacts on Earth from past to today. Specially after industrial revolution, the impact of climate change on Earth has been increasing and therefore has been focus of interest by scientists. The study of climate change has become important in terms of examining the negative effects such as drought, floods, the increase in the frequency and impact of severe hurricanes, as well as the increase of ocean and sea water levels, pH changes, salinity and temperature changes, and the melting of glaciers. The models used in this paper created using the close relationship between the ocean and the atmosphere and the use of past climate parameters, with an aim of modeling the ocean parameters for the next century. In this study, the behavior of the Black Sea water in different climate models for the next century was tried to be understood by considering the sea surface water temperature, salinity and heat exchange with the atmosphere, and comparisons between the models were included. In this study, we have analyzed the spatial and temporal variations of sea surface temperature (SST) and sea surface salinity (SSS) in the Black Sea using nine different climate models from the CMIP6 database. We have also examined the net heat flux (Qnet) and the heat transport through the Bosporus Strait, as well as the frequency and duration of marine heatwaves (MHWs) in the Black Sea. Our results show that the Black Sea is expected to experience significant warming and changes in salinity in the 21st century, with SST increasing by an average of 4.5 °C and SSS increasing by an average of 2.25 psu. These changes are expected to have significant impacts on the Black Sea ecosystem, as well as on human populations and industries in the region. Our analysis of SST and SSS using the nine CMIP6 models reveals a spatially asymmetrical pattern, with the western part of the Black Sea expected to experience greater warming than the eastern part. The multi-model mean also shows that the warming trend in the Black Sea is expected to continue in a nearly monotonic, corresponding to the increase phase of global climate change due to anthropogenic activities. Our analysis of Qnet and heat transport through the Bosporus Strait reveals that the asymmetrical warming pattern in the Black Sea is not due to heat transport from the Bosporus, but rather to net heat flux. We also found that the Rim Current system may play a role in this asymmetrical warming pattern. Our analysis of MHWs in the Black Sea shows that there is expected to be a regime shift in SST, with the frequency and duration of MHWs increasing significantly in the 21st century. In some models, the total number of days considered MHWs is projected to reach over 300 days per year by the end of the century. In conclusion, our study provides new insights into the expected impacts of global climate change on the Black Sea, highlighting the need for further research and efforts to mitigate and adapt to these changes. The asymmetrical warming pattern and the expected increase in MHWs have significant implications for the Black Sea ecosystem, as well as for human populations and industries in the region. Further research is needed to better understand the mechanisms driving these changes and to develop strategies for addressing their impacts.
  • Öge
    Fire history and climate change: Black pine forests in Western Anatolia
    (Graduate School, 2022-06-15) Şahan, Evrim Ayşe ; Dalfes, Hasan Nüzhet ; Köse, Nesibe ; 601172003 ; Earth System Science
    Wildfire is a part of the ecological processes that is highly important for the sustainability of forest ecosystems in the Mediterranean Basin. Species adapted to crown fires, such as Turkish pine, are capable of regeneration after a fire and establishing new forests. On the contrary, tree species such as black pine adapted to surface fires have regeneration problems after severe crown fires, and mass extinctions in some regions can be observed. Many studies have revealed that the fire frequency of forests in the Mediterranean Basin is expected to increase due to climate change and the fire regime of black pine forests will shift from surface fires to crown fires. In order to understand the fire regime changes in the black pine forests in the Mediterranean Basin, including Turkey, centuries-long fire records are needed. Thus, dendrochronology is one of the most reliable and effective methods commonly used in fire history studies. In this doctoral thesis, the aims are to develop a high-resolution fire reconstruction of black pine forests in Turkey, determine the seasonality of historical fires, understand the association between climate variability and fire occurrence, understand the variability of spatiotemporal patterns of fires throughout the main distribution areas of black pine forests in Turkey using tree-ring analysis, and monitor the cambium activity in black pine forest. Several spatial and temporal studies are conducted in order to understand the effects of fire management strategies, climate types or geographical gradients on regional fire regimes in the world. A large number of dendrochronology-based studies were conducted, especially in North America, to understand the spatiotemporal patterns in different geographical gradients and different climate types and also corroboration of empirical data. However, in the Mediterranean basin, a few fire history studies based on dendrochronological methods was conducted in Greece, France and Spain to understand the regional fire regime and the relationship between fire and climate. To my knowledge, there is no any conducted fire history study for any species based on tree-ring analysis in Turkey. A total of 211 samples were collected from ten sites throughout western Anatolia. The collected samples were dated by standard dendrochronological methods and the seasonality of each sample was determined. The site-level composite and regional fire chronologies were created for Kütahya, Isparta, Bolu, and western Anatolia. The major fire years were calculated with the criteria that greater than or equal to 25% of recording samples have fire scars on that year in at least two of the samples, while the regular fire years were determined by recording samples have fire scars on that year in at least two of the samples. The relationship between the major fire years and climate was analysed using Superposed Epoch Analsis. Understanding the seasonality of historical forest fires facilitates the development of concepts related to fire as an ecological and evolutionary process. In order to understand the fire regime of a region, determination of the seasonality is a must. In dendrochronology-based fire history studies, the seasonality of fire scars is mostly classified according to the intra-ring position of the fire scars as a classical method. However, studies of cambial phenology are needed to accurately correlate the position of a fire scar with the months in a year. Because the timing of the earlywood and latewood production (cambial cell production) varies according to the species, location and climate. In this context, the aim of this part of this thesis is to determine in which months the cambium activity of black pine forests starts and in which month the early/latewood cells form. In order to monitor cambium activity, a total of 144 microcores were sampled from three sites near the fire history reconstruction sites during a vegetation period (April-November 2021). Monitoring the cambial activity helped to obtain information about which month(s) are risky for forest fires. The first tree-ring based 553-year long fire history reconstruction and cambial activity of black pine forests were presented to improve our understanding of the regional fire regime components with the effect of climate in Turkey. The fire return interval of black pine forests in Anatolia was calculated from a minimum of one year and a maximum of 105-year intervals over the study period. The seasonality of most of the fire scars in western Anatolia occurred in the latewood period. As conducted in a cambial activity study of black pine forests in western Anatolia, latewood tracheid cells are formed from (August in Isparta) from September to November. Since most of the fires in western Anatolia occur in latewood, the risky months for fires in the study area are from (July in Isparta) August to November (the late summer and autumn) based on xylogenesis studies. The relationship between climate and fire years calculated with regional fire chronologies showed that the major fires in Kütahya and Bolu are associated with dry years, while the wet conditions two years prior to major fire events in Isparta. The decrease in fire frequency was observed in the late 19th and early 20th centuries due to human-induced fire suppression activities. That can cause the accumulation of combustible material and pose a risk for more intense fires. Based on future climate projections, as a result of increased drought frequency, we will face extended fire seasons that may shift the fire regime from the surface to crown fires and even cause mega fires. A large number of simultaneous fires were recorded in the period between the mid-1800s and the early 1900s. The decrease in fire frequency after the early 1900s coincides with the first forest protection law in 1937. As a result of the comparison of fire years in western Anatolia, Spain, and Greece, more common fire years were found in studies of Greece than in Spain. The differences in climate conditions of the eastern and western Mediterranean due to frontogenesis or depressional activity might explain these different common fire years. The year 1879 was the most extensive fire year in Greece in the 19th century and it was recorded as one of the most common fire years in western Anatolia. The year 1945 was the only common fire year in the Mediterranean region sites. Results in this study showed that the fires in 1945, observed simultaneously in Anatolia, Greece, and Spain, occurred in the most severe and widespread drought among the spatially visualized common fire years. In this study, long-term fire history data were developed by using dendrochronological methods to understand the fire regime of black pine forests for the first time in Turkey. These fires were analyzed with a new approach with the determination of the seasonality by taking samples with microcores. Unlike studies only current fires are analyzed or fire history reconstructions, the results were obtained by integrating both ecological and statistical methods.