Browsing by Author "Tayfur, Gokmen"

Now showing 1 - 9 of 9

Citation - WoS: 9
Citation - Scopus: 11
A Joint Evaluation of Streamflow Drought and Standard Precipitation Indices in Aegean Region- Turkey
(SPRINGER BASEL AG, 2023) Ayse Gulmez; Denizhan Mersin; Babak Vaheddoost; Mir Jafar Sadegh Safari; Gokmen Tayfur; Tayfur, Gokmen; Vaheddoost, Babak; Safari, Mir Jafar Sadegh; Mersin, Denizhan; Gulmez, Ayse
Water is an invaluable substance that ensures the life cycle and causes hydrologic events worldwide. Water deficit also known as drought is a naturally occurring disaster that affects the hydrometeorologic and/or climatic responses in time and space. In this study the meteorologic and hydrologic droughts in Buyuk Menderes Kucuk Menderes and Gediz basins in Turkey are investigated. The streamflow drought index (SDI) and standard precipitation index (SPI) are used considering different time windows. To achieve this the monthly streamflow at Cicekli-Nif Besdegirmenler-Dandalas Bebekler-Rahmanlar and Kocarli-Koprubasi hydrometric stations together with monthly precipitation at 14 meteorologic stations during 1973-2020 (47 years) are used. The SDI and SPI with 1 3 6 and 12 months moving average are then used to express the association between the meteorologic and hydrologic droughts in the basin. Results showed that the SDI depicts no abnormal situations while the SPI rates in the 1980s and 2010s indicated severe droughts. It was concluded that the inner parts of the basins are prone to frequent droughts and there is a concordance between SPI and SDI patterns at the basin level. However minor discrepancies between SPI and SDI do exist and probably originated from temporal delays and water abstraction.
Citation - WoS: 3
Citation - Scopus: 2
Assessing the Spatial and Temporal Characteristics of Meteorological Drought in Afghanistan
(Birkhauser, 2025) Gökmen Tayfur; Ehsanullah Hayat; Mir Jafar Sadegh Safari; Tayfur, Gokmen; Hayat, Ehsanullah; Safari, Mir Jafar Sadegh
Afghanistan is suffering from periodic events of drought which has exacerbated in recent years due to extreme climate events in the region. Having an arid to semi-arid climate the country faces significant challenges of water resources management especially for irrigation as reliance on agriculture is cumbersome. This study is undertaken to characterize historical meteorological drought in Afghanistan to provide an insight on where and when meteorological drought events happened in different River Basins (RBs). The study mainly employs the gamma-Standardized Precipitation Index (gamma-SPI) to analyze historical meteorological droughts across Afghanistan from 1979 to 2019. Monthly precipitation data is obtained from the Ministry of Energy and Water (MEW) of Afghanistan which is a combination of observed data from ground stations and gap-filled data by the MEW for the study period. Gridded gamma-SPI values are interpolated and mapped to visualize patterns of spatial drought across the entire country. The results indicate that countrywide extreme drought events occurred in 1999 2000 2001 2010 2016 2017 and 2019 particularly affecting southern western and southwestern regions. Decreasing rainfall occurred in all five RBs with the most considerable decline observed in the 1999–2008 period. The study reveals the increasing frequency and severity of meteorological droughts in Afghanistan. It also emphasizes on the vulnerability of agriculture and water sectors due to the drought events. The findings of the study suggest the need for better drought monitoring preparedness awareness and adaptation of strategies to ensure water security and agricultural sustainability in the face of climate change. © 2025 Elsevier B.V. All rights reserved.
Assessing the Spatial and Temporal Characteristics of Meteorological Drought in Afghanistan (Nov- 10.1007/s00024-024-03578-x- 2024)
(SPRINGER BASEL AG, 2025) Gokmen Tayfur; Ehsanullah Hayat; Mir Jafar Sadegh Safari; Tayfur, Gokmen; Hayat, Ehsanullah; Safari, Mir Jafar Sadegh
Assessment of Drought in Izmir District Using Standardized Precipitation Index
(Springer Nature, 2025) Tayfur, Gokmen; Vaheddoost, Babak; Safari, Mir Jafar Sadegh; Mersin, Denizhan; Gulmez, Ayse
Developing feasible structural flood mitigation measures for arid regions using hydrological and hydraulic modelling: a case of Baledweyne City Somalia
(Springer Science and Business Media Deutschland GmbH, 2025) Abdullahi Abdulwahid Ibrahim; Gökmen Tayfur; Mir Jafar Sadegh Safari; Tayfur, Gokmen; Ibrahim, Abdullahi Abdulwahid; Safari, Mir Jafar Sadegh
Flood mitigation measures are essential in several aspects of environmental sustainability such as environmental protection and development infrastructure resilience and climate change adaptation strategies. This study investigates several remedial measures such as flood and disaster risk reduction strategies to protect Baledwayne City Somalia. The developed hydrological-hydraulic model is successfully calibrated using the 2019 flood event. Inundation maps for different mitigation measures are developed to determine the most appropriate one(s) that may reduce flood impact and protect the city especially the residential areas against peak discharge of a 500-year return period. The investigated mitigation measures include (1) operating the Warabole Diversion Canal (2) building two detention ponds at the upstream sections of both right and left floodplains (3) building levees (dikes) along both sides of Shabelle River and (4) restoration of the river. Results show that the remedial measures for the Warabole Diversion Channel and the river restoration are insufficient to protect the city. Building ponds on the right- and left-hand sides of the river substantially protects the city from flooding by reducing the flooded area from 88.6 to 31.5 km2 which is equivalent to a reduction of 35.5%. Construction of dikes on both sides of the river does not protect the city by overflowing an area of 75.2 km2 (84.9%). A combination of several measures is also investigated and it is found that ponds must be built along with any alternative measure. When all four measures are combined it becomes clear that the city’s residential areas would be fully protected significantly reducing the overall flooded area of the city to 27.9 km2 (31.5%). These flooded areas are behind the detention pond which is designed to hold floodwater and gradually drain it back to the river. © 2025 Elsevier B.V. All rights reserved.
Citation - WoS: 26
Citation - Scopus: 31
Drought Assessment in the Aegean Region of Turkey
(SPRINGER BASEL AG, 2022) Denizhan Mersin; Ayse Gulmez; Mir Jafar Sadegh Safari; Babak Vaheddoost; Gokmen Tayfur; Tayfur, Gokmen; Vaheddoost, Babak; Safari, Mir Jafar Sadegh; Mersin, Denizhan; Gulmez, Ayse
Drought indices are commonly used to monitor the duration and severity of droughts. In this regard the continuously changing climate regardless of its cause or effect pushes the limit of the water deficit through time and space. Izmir is a raising city in Turkey which owns various water resources including but not limited to seashores lakes river streams and groundwater aquifers. In this study the long-term precipitation and temperature records from 14 meteorological stations between 1973 and 2020 (for 47 years) are used to investigate the drought characteristics in Buyuk Menderes Kucuk Menderes and Gediz basins located in the Aegean region of Turkey. For this the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) Percent of Normal (PNI) and the so-called Discrepancy Precipitation Index (DPI) are used with consideration to 1- 3- 6- and 12-month moving averages to investigate the drought patterns. Results showed that the monthly indices depict very similar results for the entire region. However in the 1980s and 2010s droughts were more severe than the rest of the historical records. When the moving average operator is implemented in the analysis (3- 6- and 12-month periods) neither SPI nor the SPEI showed the same results at any stations. It is illustrated that the periods of severe and normal drought have occurred in the past yet the indices that are obtained using average values are generally within the normal limits but extreme values (extremely arid or extremely wet) occurred occasionally. It is also concluded that although there is a similarity between the implemented indices the DPI and PNI depict the highest resemblance.
Citation - WoS: 3
Citation - Scopus: 3
Ensemble and optimized hybrid algorithms through Runge Kutta optimizer for sewer sediment transport modeling using a data pre-processing approach
(Elsevier B.V., 2023) Enes Gul; Mir Jafar Sadegh Safari; Omerul Faruk Dursun; Gökmen Tayfur; Tayfur, Gokmen; Dursun, Omer Faruk; Safari, Mir Jafar Sadegh; Gul, Enes
Uncontrolled sediment deposition in drainage and sewer systems raises unexpected maintenance expenditures. To this end implementation of an accurate model relying on effective parameters involved is a reliable benchmark. In this study three machine learning techniques namely extreme learning machine (ELM) multilayer perceptron neural network (MLPNN) and M5P model tree (M5PMT), and three optimization approaches of Runge Kutta (RUN) genetic algorithm (GA) and particle swarm optimization (PSO) are applied for modeling. The optimization and ensemble hybridization approaches are applied in the modeling procedure. For the case of hybrid optimized models the ELM and MLPNN models are hybridized with RUN GA and PSO algorithms to develop six hybrid models of ELM-RUN ELM-GA ELM-PSO MLPNN-RUN MLPNN-GA and MLPNN-PSO. Ensemble hybrid models are developed through coupling the ELM and MLPNN models with the M5PMT algorithm. The data pre-processing approach is applied to find the best randomness characteristic of the utilized data. Results illustrate that the RUN-based hybrid models outperform the GA- and PSO-based counterparts. Although the MLPNN-RUN and MLPNN-M5PMT hybrid models generate better results than their alternatives MLPNN-M5PMT slightly outperforms MLPNN-RUN model with a coefficient of determination of 0.84 and a root mean square error of 0.88. The current study shows the superiority of the ensemble-based approach to the optimization techniques. Further investigation is needed by considering alternative optimization techniques to enhance sediment transport modeling. © 2023 Elsevier B.V. All rights reserved.
Citation - WoS: 37
Citation - Scopus: 40
Historical Trends Associated with Annual Temperature and Precipitation in Aegean Turkey Where Are We Heading?
(MDPI, 2022) Denizhan Mersin; Gökmen Tayfur; Babak Vaheddoost; Mir Jafar Sadegh Safari; Tayfur, Gokmen; Vaheddoost, Babak; Safari, Mir Jafar Sadegh; Mersin, Denizhan
The trend analysis of annual temperature (daily average) and total precipitation has been conducted for 14 stations located in the Aegean Region Turkey. The Sen Spearman’s rho and Mann-Kendall test methods are used in the detection of the historical trends in the region. The Pettitt test is also implemented to find the significance of the trend while the Theil-Sen approach is applied to detect the change point(s) in the time series. Findings of the following study indicate that both precipitation and temperature time series in the selected stations depict statistically significant trends with increasing nature. The rate of increase in precipitation and temperature by the Theil-Sen test is found to be 4.2–7.9 mm/year and 0.20–0.35 °C/decade respectively. It is also found that the turn points of the temperature trends determined by the Pettitt test occurred in 1998 for all the stations. According to the results the magnitude of the extreme events would change in the future which may help in conceptualizing the framework and the resilience of the infrastructures against climate change. © 2022 Elsevier B.V. All rights reserved.
Citation - WoS: 17
Citation - Scopus: 22
Meteorological Drought Assessment and Trend Analysis in Puntland Region of Somalia
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Nur Mohamed Muse; Gökmen Tayfur; Mir Jafar Sadegh Safari; Tayfur, Gokmen; Muse, Nur Mohamed; Safari, Mir Jafar Sadegh
Drought assessment and trend analysis of precipitation and temperature time series are essential in the planning and management of water resources. Long-term precipitation and temperature historical records (monthly for 41 years from 1980 to 2020) are used to investigate annual drought characteristics and trend analysis in Somalia’s northern region. Six drought indices of the normal Standardized Precipitation Index (normal-SPI) the log normal Standardized Precipitation Index (log-SPI) the Standardized Precipitation Index using the gamma distribution (Gamma-SPI) the Percent of Normal Index (PNI) the Discrepancy Precipitation Index (DPI) and the Deciles Index (DI) are used in this study for the annual drought assessment. The log-SPI the gamma-SPI the PNI and the DPI could capture historical extreme and severe droughts that occurred in the early 1980s and over the last two decades. The results indicate that Somalia has gone through extended drought periods over the past quarter century exacerbating the existing humanitarian situation. The normal-SPI gamma-SPI and PNI indicate less and moderate drought conditions whereas log-SPI DPI and DI accurately capture historical extreme and severe drought periods, thus these methods are recommended as annual drought assessment tools in the studied region. Not only are the PNI and DPI less correlated to each other but their correlation coefficient (CC) with SPI-based drought indices are not as high as SPI-based indices which are close to unity. For the purpose of the trend analysis the Mann Kendall (MK) test the Spearman’s rho (SR) test and the Şen test are used. Furthermore the Pettitt test is implemented to detect the change points and the Thiel-Sen approach is used to estimate the magnitude of trend in the precipitation and temperature time series. The results indicate that there is overall warming in the region which has experienced a significant shift in trend direction since 2000. The trend analysis of annual precipitation data time series shows that Bossaso and Garowe stations have significant positive trends while the Qardho station has no trend. In 1997 and 1998 respectively abrupt changes in annual precipitation are detected at Qardho and Garowe stations. Due to the civil war of more than three decades in Somalia and the non-institutionalized governance to inform historical drought conditions in the country determining the most appropriate meteorological drought index would help to develop a drought monitoring system for states and the entire country. © 2023 Elsevier B.V. All rights reserved.