Impacts of climate nonstationarities on hydroclimatological variables in turkey

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2018



Supervisor: İSMAİL YÜCEL


Using multiple nonstationary frequency distributions, this study investigated the impacts of nonstationarities on yearly and seasonal extremes of hydroclimatological variables for observations and CORDEX projected data of period 2050-2100 in Turkey. Future streamflow is generated using the calibrated HBV-light hydrological model. Evaluation of CORDEX models suggests that for precipitation RCMs originated from GCMs EC-EARTH and HadGEM2-ES and for temperature GCM HadGEM2-ES coupled with RCM CCLM4-8-17 showed better agreement with observations. GEV distribution fits observation better than other distributions for all variables. During historical period generally in Turkey, and particularly in the eastern part, nonstationarity impacts are positive on yearly as well as seasonal temperature maxima (up to 5°C) and minima (up to 10°C). These impacts are amplified during the projection period. For observed precipitation, positive impacts (up to 50%) are recorded for yearly maxima but many stations, particularly in South-Eastern Anatolia, Central Anatolia, and Eastern Anatolia, exhibited negative impacts (up to 40%). Mostly positive impacts are found during the projection period for vi yearly and seasonal precipitation maxima. Some reversal in the impact type also appeared from the current to the future period. In Upper Euphrates basin, for annual high flows, four sub-basins showed positive impacts (up to 12%) and four sub-basins showed negative impacts (up to 30%) however mostly positive impacts are obtained for annual and seasonal maxima of low flows. Bias-adjusted RCMs tend to lose the nonstationarity signal for precipitation. It is suggested that in the operational and planning strategies of existing and new hydraulic structures, the nonstationarity approach should be taken into account to be in the safe side and economical scale. More precautions should be given to water conservation as milder minimum temperatures might contribute to less snowpack in mountainous regions.