AYBE- İklim ve Deniz Bilimleri Lisansüstü Programı - Doktora
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Konu "Climate change" ile AYBE- İklim ve Deniz Bilimleri Lisansüstü Programı - Doktora'a göz atma
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ÖgeInvestigating The Hydroclimatic Changes İn The Euphrates-tigris Basin Under A Changing Climate(Eurasia Institute of Earth Sciences, 2019-03-25) Yılmaz, Yeliz ; Şen, Ömer Lütfi ; 601122003 ; Climate and Marine Sciences ; İklim ve Deniz BilimleriFrom the beginning of human history, the transboundary waters of the Euphrates and Tigris Basin (ETB) have been the main freshwater resources of the Middle East region. The basin is located on the territories of four major riparian countries (Iraq, Turkey, Iran, and Syria). These waters have been primarily used for irrigation, energy production, domestic use, and livestock. The Euphrates and the Tigris rivers are fed by the snowmelt from the surrounding high mountains. Previous studies showed that the waters of these two rivers are being affected by anthropogenic climate change. However, particularly the modeling studies did not include the effects of the extensive irrigation schemes that have been applied within the scope of the Southeastern Anatolian Project (GAP). GAP is the largest regional development project carried out by Turkey within the headwaters of the basin. GAP includes such investments as irrigation schemes and the construction of major dams. At the current stage of GAP, 22 dams and 19 hydroelectric power plants have been planned, and over the one fourth of the planned irrigation projects are complete. In the future, a total area of approximately 1.8 million hectares will be irrigated. Since the beginning of 90s, the applied irrigation plans have already caused massive land use and land cover (LULC) changes in the region. We estimate that the water resources of the region will be more vulnerable due to the combined effects of greenhouse forcing and LULC changes. In this thesis, we carefully investigate the effects of human-induced changes on the regional climate and water budget of the ETB. The research questions of the thesis are designed holistically with the previous studies about the basin in mind. For this purpose, we conducted comprehensive research under four main topics. First, several remote sensing products and a meteorological reanalysis data set were analyzed for the Near East region. The relationship between the decline in the water resources and snowpack is investigated. Secondly, the outputs of several General Circulation Models (GCMs) from CMIP5 were compared over the basin in order to find the "best" performing GCM in simulating the climate of the region. The outputs of the selected GCM are used as initial and boundary conditions to force the regional climate model for dynamical downscaling. Thirdly, the hydroclimatic effects of the LULC changes are assessed by comparing the results of three simulations. These simulations are performed under the current climate conditions by using three land use map that show the different irrigation levels. We also analyzed these outputs to conduct an extreme value analysis in order to understand the effects of irrigation on regional maximum temperatures. Lastly, we investigated the combined effect of the changes in the atmospheric composition and LULC. We calculated the water budgets of the headwaters and the GAP region under the changing climate. Gravimetric satellite data from GRACE is used to investigate the terrestrial water resources of the basin, and to calculate the change in trends. Globally available GRACE data give information on the terrestrial water storage anomalies between 2002 and 2016. We found that the Euphrates and Tigris Basin has a negative water storage anomaly trend of 27.4 mm per year for the areas above 1000 m. Our finding is consistent with the results from previous studies which use the same data set but for a shorter time period. As the reason of the decline in water resources, they pointed out the groundwater use particularly after the long-term drought in 2007. In this study, we claim that there is a significant relationship between the decline in both water resources and the montane snowpack in the headwaters. Owing to the sparse observational network in the Near East region, we employed several remotely sensed satellite products (optical, passive microwave, and gravimetric) and a new meteorological reanalysis data set in order to analyze the snowpack in the ETB. Comparisons between the GRACE and the remote sensing products showed statistically significant correlations for different elevation thresholds. Moreover, high resolution MODIS data indicate a worrying reduction in snow-cover duration. We calculated significant declines up to 4 weeks per decade for the areas above 1000 m, particularly over the Taurus and Zagros mountains known as headwaters of the basin. In order to select a GCM amongst the CMIP5 models that represents the climate of Turkey and the Euphrates and Tigris Basin, we analyzed several temperature and precipitation outputs between 1971 and 2000. Those outputs were compared with a high resolution (0.5°x0.5°) gridded observational data set, namely Climate Research Unit (CRU). Since all models have different spatial resolutions, model outputs were regridded to the spatial resolution of CRU. Then, these models were ranked according to their statistics. We also used the Taylor diagrams to detect the GCM that produces similar values to the observations. Since the focus of the study is on the water budget, the weight is given to the precipitation performance of the models. As a result, the EC-EARTH model was selected to drive the regional climate model for the future scenarios. A regional climate model, RegCM4, was employed to simulate the individual and combined effects of irrigation induced LULC changes and climate change. Historical simulations were produced by using three different land use maps which reflect the increase of irrigated and dammed areas. These three maps were created by using the data from the European Environmental Agency and the Turkish State Hydraulic Works based on the default land use map of RegCM4. Results of a reanalysis data set (NNRP) were used to force the RegCM4 model in order to produce dynamically downscaled high resolution regional data over the Eastern Mediterranean and Black Sea region in 48 km, and in a nested domain over Turkey in 12 km. By enabling the subgrid feature of the land surface model of RegCM4, land surface variables were computed at a horizontal resolution of 3 km. To evaluate the model results, CRU temperature and precipitation data, and Global Land Data Assimilation System (GLDAS) evapotranspiration data were used. Comparisons between these three simulations revealed that irrigation causes a local cooling over the GAP region (up to 0.8 °C) and a slight increase in precipitation (spatially averaged 7%). Simulation results indicate that irrigation projects have significantly altered the regional water budget due to an increase in evapotranspiration of around 51% (partly irrigated) and 114% (fully irrigated) compared to pre-GAP conditions. The dramatically increasing water demand of the semi-arid irrigated region is currently barely compensated by the headwaters of the ETB. Taking into account the committed water release to the downstream countries shows that there might not be enough water for all the planned irrigation schemes in the GAP region. These concerning results are found by assuming that the current climate conditions are stationary. However, the future projections from the previous studies pointed towards the changing climate conditions due to anthropogenic greenhouse gas emissions. For this purpose, we performed future simulations by forcing the RegCM4 model with the outputs of EC-EARTH and adding the planned irrigation schemes on them. Future simulations are produced with two scenarios (RCP4.5 and RCP8.5) for the middle (2046-2065) and the end (2081-2100) of the century. To be able to account for the LULC changes, we also used two land use maps that show no irrigation and fully irrigated conditions. In this way, we addressed both individual and integrated effects of LULC change and greenhouse forcing. The results from future simulations for mid-century show an insignificant temperature increase over the GAP region due to irrigation's cooling effect. But, this cooling effect is completely local. Significant temperature increases are projected up to 2.5 °C in the rest of Turkey. Moreover, the severe scenario (RCP8.5) estimates that increase in temperature reaches up to 5 °C at the end of the century, while this change is around 2 °C in the GAP region. The simulations with RCP4.5 scenario produced a slight increase in precipitation for both future periods, a decline in precipitation is projected with RCP8.5 scenario. Lastly, as in the historical simulations, significant increase in evapotranspiration is estimated in the GAP region. So, water loss through evapotranspiration is projected to have higher values. Hence, the future water budget for fully irrigated conditions indicates that water storage in the headwaters is not enough for the water demand of the GAP region. Taking into account the water release to the downstream countries (15.8 billion m3 per year) shows that future irrigation plans are unsustainable. Even if this water will not be released, the water needed for irrigation in the GAP region is projected to be more than the stored water in the headwaters according to the severe scenario at the end of the century. The results of the thesis paint a bleak picture for future water availability in the ETB in case of continuing on the current water use plans. In the previous studies, it is showed that using different irrigation techniques can help to reduce water loss by increasing the irrigation efficiency. Another adaptation method is to build new deeper dams with a smaller surface area in the colder headwaters. Additionally, the sustainability of the planned irrigation schemes can be reevaluated by considering the results from future projections. The water dispute in the ETB among the riparian countries is a long-standing complex issue of transboundary water sharing. The water loss through the increased evapotranspiration may play a crucial role in shaping the future of water resources management and policies in this water-stressed region.