Impacts of climate nonstationarities on hydroclimatological variables in Turkey

Aziz, Rizwan
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.


Nonstationarity impacts on frequency analysis of yearly and seasonal extreme temperature in Turkey
Aziz, Rizwan; Yücel, İsmail; Yozgatlıgil, Ceylan (Elsevier BV, 2020-07-01)
This study investigates the temporal variability in yearly and seasonal extreme temperatures across Turkey using stationary and nonstationary frequency analysis. The analyses are conducted using Generalized Extreme Value (GEV), Gumbel and Normal distributions for minimum and maximum temperatures during historical (1971-2016) and projection period (2051-2100). The future nonstationarity impacts are quantified using a 12-member ensemble of The Coordinated Regional Downscaling Experiment (CORDEX) regional clim...
Evaluation of a satellite-based global flood monitoring system
Yılmaz, Koray Kamil; Tian, Yudong; Hong, Yang; Pierce, Harold F. (2010-01-01)
This study provides an initial evaluation of a global flood monitoring system (GFMS) using satellite-based precipitation and readily available geospatial datasets. The GFMS developed by our group uses a relatively simple hydrologic model, based on the run-off curve number method, to transform precipitation into run-off. A grid-to-grid routing scheme moves run-off downstream. Precipitation estimates are from the TRMM Multi-satellite Precipitation Analysis (TMPA). We first evaluated the TMPA algorithm using a...
Production of a high-resolution improved radar precipitation estimation map using gauge adjustment bias correction methods
Yousefi, Kaveh Patakchi; Yılmaz, Mustafa Tuğrul; Ozturk, Kurtulus; Yücel, İsmail; Yılmaz, Koray Kamil (null; 2020-05-08)
This study evaluates relative performances of different statistical algorithms to enhance radar-based quantitative precipitation estimation (QPE) accuracy using rain gauge network data. Initial investigations are implemented using observations obtained via 17 C-band radars located over different regions of Turkey. It was observed that there is an underestimation problem in radar estimations compared with the ground observations. According to the initial results, daily mean bias for radar estimations over di...
Comparison of missing value imputation methods in time series: the case of Turkish meteorological data
Yozgatlıgil, Ceylan; İyigün, Cem; Batmaz, İnci (2013-04-01)
This study aims to compare several imputation methods to complete the missing values of spatio-temporal meteorological time series. To this end, six imputation methods are assessed with respect to various criteria including accuracy, robustness, precision, and efficiency for artificially created missing data in monthly total precipitation and mean temperature series obtained from the Turkish State Meteorological Service. Of these methods, simple arithmetic average, normal ratio (NR), and NR weighted with co...
Quality and Homogeneity Analysis of Precipitation Data in North Cyprus
Yanmaz, Ali Melih; Akıntuğ, Bertuğ (2018-09-14)
This study aims to reveal procedures for testing and creating a set of complete, quality-controlled, and homogeneous precipitation data sets in North Cyprus. Database involves 37 daily precipitation series which are uniformly distributed throughout the study area with observation periods ranging from 1976 to 2015. As a first step of the procedures, the estimation of the missing values is carried out considering a range of distances with various estimation methods based on neighboring stations...
Citation Formats
R. Aziz, “Impacts of climate nonstationarities on hydroclimatological variables in Turkey,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.