Climate change now tops the list of challenges facing water resources, because it changes not only averages but also the regularity, intensity, and timing of rainfall. The thesis under discussion addresses this challenge in the Middle Euphrates region, trying to answer a specific question: how will the climate of this region change in the coming decades, and what will be the impact on drought and surface runoff? The thesis begins with the global picture: according to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the Earth’s temperature rose by about 0.85°C between 1880 and 2012. If emissions continue on their current path, this century may add a rise of between 1.1 and 4.6°C. This is reflected in changing precipitation patterns and an increased likelihood and severity of drought, and these risks are greater in arid and semi-arid regions. The Middle East is among the most affected regions, and Iraq is among its most vulnerable countries, as studies project reduced available water, more frequent heat waves and dust storms, and sudden floods. To gauge the scale of local warming, the thesis relies on an earlier study in southwestern Iraq, which projected a temperature rise of 1.78 to 2.07°C during 2040–2069 under the moderate scenario RCP4.5, and 2.2 to 2.63°C during 2070–2099. Under the high scenario RCP8.5, the increase reaches 2.18 to 2.85°C, then 2.93 to 3.7°C, in the same two periods. These figures show that the gap between the two scenarios widens over time, and that what we do about emissions today determines the extent of warming decades from now. To translate global projections into local detail, the study used five global climate models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5): CanESM2, CSIRO-Mk3.6.0, HadGEM2-ES, MIROC5, and NorESM1-M. These models have coarse spatial resolution, with grid cells between 1.2 and 2.8 degrees, so they cannot by themselves describe the climate of a city or a small basin. For this reason, a downscaling technique was used, which links changes in the global model to local station data. The downscaling tool here is the LARS-WG weather generator, version 6. It analyzes data from a single station, namely daily rainfall and maximum and minimum temperatures, and extracts their statistical characteristics into dedicated files. It then generates artificial daily series that mimic these characteristics, adjusting their parameters according to the changes projected by the global models under each scenario. Before relying on it, it was calibrated against 1991–2020 data, and the correlation between observed and simulated values was 0.97 to 0.99 for rainfall and about 0.999 for maximum and minimum temperatures, with temperature error ranging from roughly 0.19 to 0.33°C. These results give confidence that the generated series represent the climate of the five stations. After generating the future series, the study assessed the impacts of climate change using two drought indices. It concluded that droughts in the Middle Euphrates will be longer and more severe during 2021–2060, with the peak of risk concentrated around the middle of the century. For example, the most severe drought in Diwaniyah is projected between 2050 and 2052, with an intensity of about -2.97 according to the SPEI index, which captures the effect of temperature, and the longest drought in Samawah is projected to last about two and a half years, between 2050 and 2053. This indicates that rising temperatures add a new burden on top of the deficit caused by low rainfall. The study did not stop at drought; it also fed the climate series into the HEC-HMS model to measure their impact on runoff. The results were mixed. In Diwaniyah, the projected peak flow ranged from an increase of about 5% to 15% under the moderate scenario, to a decrease of about 25% to 37% under the high scenario, depending on the year studied. In Hillah, results varied between increase and decrease from one year to another. This means that climate change does not imply only steady drying, but also greater fluctuation between scarce years and others that may produce sharp runoff peaks, which calls for preparing for both at once. The thesis points out the limits of these projections. They rely on satellite-derived rainfall data, on climate models that differ from one another, and on emission scenarios that are assumptions about the future, not predictions. The results should therefore be read as possible trends that help with planning, not as final figures. The thesis concludes with clear recommendations: reducing greenhouse gas emissions and shifting to clean energy; expanding the hydrological analysis to cover other basins in the Mesopotamian plain; and incorporating river inflows and more diverse climate scenarios into drought studies to reduce uncertainty. The core message is that adapting to the new climate begins with an accurate understanding of what awaits each basin individually, followed by water planning that balances the risks of scarcity against the risks of floods. Presented by: Zahraa Hussein Mohammed (Assistant Lecturer) Source: Zahraa Hussein Mohammed Aziz (2024). Projections of Climate Changes in Hydrological Regime of the middle Mesopotamian plain