Effects of climate change on water resources in Omerli basin

Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2014

Thesis Language: English


Principal Supervisor (For Co-Supervisor Theses): İsmail Yücel

Co-Supervisor: Sevda Zuhal Akyürek


This study investigates the impacts of climate change on water resources through precipitation and discharge analyses in Omerli catchment Istanbul, Turkey. Precipitation and temperature data are obtained from GCM (Global Circulation Model)/RCM (Regional Climate Model) combinations based on A1B carbon scenario via Europen Union (EU)-ENSEMBLESproject. The data is obtained at 25 km resolution on daily time scale for reference period between 1960 and 1990 and future period between 2071 and 2100. The HBV (Hydrologiska Byråns Vattenbalansavdel-ning) model is used to investigate discharge properties of study area. First the HBV is calibrated by some of catchment properties along with PEST (parameter estimation) method. Because RCM scale is comparatively coarse (25 km) for catchment scale its results are downscaled to 1 km using the Geographically Weighted Regression (GWR) method. RCM precipitation with and without GWR method are evaluated for characteristics of extreme precipitation events and they are used in the HBV model for estimating the extreme discharges along with reference and future periods. All RCMs strongly underestimate precipitation. GWR improves underestimation tendency of RCMs precipitation especially for extreme events. Depending on precipitation inputfrom RCMs with and without GWR the HBV also shows significant underestimation in daily and extreme runoff but it provides better estimates with GWR input. The magnitude ofextreme events increases in winter, spring, and summer but decreases in fall from reference to future period. Return periods of the extreme events increase in the future period and therefore, Omerli Basin is under water stress with changing climate.