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İstanbul Teknik Üniversitesi (2019)

Investigating The Hydroclimatic Changes İn The Euphrates-tigris Basin Under A Changing Climate

Yılmaz, Yeliz ;

Titre : Investigating The Hydroclimatic Changes İn The Euphrates-tigris Basin Under A Changing Climate

Değişen İklim Koşulları Altında Fırat-Dicle Havzası’ndaki Hidroiklimsel Değişikliklerin İncelenmesi

Auteur : Yılmaz, Yeliz ;

Université de soutenance : İstanbul Teknik Üniversitesi

Grade : Doctor of Philosophy (PhD) 2019

Résumé partiel
From 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.

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Page publiée le 16 décembre 2020