İlgi alanları

• MakaleYalnız künye2026/r/bayburt/11185
  Depth-dependent predictability of soil temperature under Mediterranean climatic conditions: a frequency-based perspective

  Guleryuz, Didem; Yıldırım, Ümit; Güler, Cüneyt

  Soil-temperature predictability is inherently depth-dependent because atmospheric forcing is progressively attenuated and transformed into smoother, lower-frequency thermal dynamics with increasing depth. Under Mediterranean climatic conditions, where pronounced seasonality and strong surface forcing coexist, this depth-dependent transformation provides an informative basis for evaluating model behaviour. This study examines soil-temperature prediction at depths of 5, 10, 20, 50, and 100 cm using a multivariate dataset comprising 5,285 retained daily observations from the Mersin meteorological station on Türkiye’s eastern Mediterranean coast. Precipitation, air temperature, relative humidity, wind speed, and evaporation were used as predictors. Support vector regression, random forest, and LightGBM were evaluated using R², RMSE, and MAE. All three models performed strongly in the near-surface layers, with test R² values ranging from 0.948 to 0.954 at depths of 5–20 cm. Predictive performance declined with increasing depth as short-period variability weakened and the thermal signal became smoother and more seasonally structured. RF and LightGBM showed a greater numerical decline at 50–100 cm, whereas SVR achieved test R² values of 0.923 at 50 cm and 0.847 at 100 cm; however, inter-model differences remained modest and were interpreted descriptively. Lomb–Scargle spectral analysis, applied using the actual observation dates, indicated that short-period variability became relatively less pronounced with depth while seasonal-scale and low-frequency components remained prominent. Overall, the findings suggest that soil-temperature prediction should be interpreted in relation to depth-dependent temporal signal characteristics rather than as a search for a universally superior algorithm.

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• MakaleYayıncıda açık erişim2025Scopus SJRQ1/r/bayburt/10802
  Innovative governance for sustainable management of Mediterranean coastal aquifers: Evidence from Sustain-COAST living labs

  Ceseracciu, Chiara; Nguyen, Thi Phuoc Lai; Deriu, Romina; Branca, Giampiero; Vozinaki, Anthi-Eirini K.; Karatzas, George P.; Mellah, Thouraya; Akrout, Hanene; Yildirim, Uemit; Kurt, Mehmet Ali

  This study focuses on groundwater governance in Mediterranean socio-ecological systems, where anthropogenic and climate-related pressures lead to issues such as overexploitation, salinisation, and pollution, particularly in coastal areas. It provides empirical evidence of the practices and processes that foster governance learning and innovation towards adaptive and sustainable groundwater management, drawing on data from a comparative groundwater governance assessment of four case studies,each representing relevant issues within the mosaic of water challenges in the Mediterranean region. This study addresses several knowledge gaps by proposing a framework aligned with a socio-ecological systems approach, allowing for acomprehensive understanding of groundwater governance by consideringinterconnected social, economic, and environmental dimensions. The assessment process integrates diverse data and knowledge sources, and ensures the active participation of local stakeholders. The findings highlight several cross-cutting themes relevant to water governance innovation. These include transdisciplinary collaborations that recognise the multidimensionality of water governance, the role of cultural and social capital as catalysts for community mobilisation, the potential of community participation tools to promote voluntary behavioural changes, and the creation of social learning spaces to co-design scientifically robust and socially acceptable water management options. Furthermore, this study emphasises the integration of the Theory of Change to effectively engage stakeholders in the co-creation of tailored governance solutions, thereby enhancing the potential for sustainable policy outcomes.

  AtıfScopus17·WoS15

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• MakaleYayıncıda açık erişim2024/r/bayburt/13132
  Pollution Source and Soil Quality Assessments of Heavily Contaminated Soils by Selected Potentially Toxic Elements in a Human-Degraded Wetland Area

  Kurt, Mehmet Ali; Yalçın, Sezen; Güler, Cüneyt; Güven, Onur; Yıldırım, Ümit

  Wetlands are transitional between terrestrial and aquatic environments and have essential ecological functions. Unfortunately, due to anthropogenic activities and climate change, the area covered by wetlands is gradually decreasing worldwide, causing deterioration and loss of their critical and vital ecological functions. One of these degraded wetlands is the Hürmetçi Sazlığı, a nationally important wetland located in the Kayseri Province of Turkey. This study aims to determine the spatial and vertical (depth profile) distribution and the sources of the potentially toxic elements (PTEs) As, Cd, Pb, and Zn in the soils around the Hürmetçi Sazlığı Wetland (HSW) and to evaluate environmental risk factors using various soil quality indicators. According to the results obtained, it was determined that some parts of the wetland soils were significantly polluted in terms of As, Cd, Pb, and Zn. The concentrations (in mg/kg) of these PTEs in the soil around the wetland ranged between 9.12 and 273.9 for As, 0.38 and 1119.46 for Cd, 3.59 and 1807.66 for Pb, and 41.68 and 77,287.5 for Zn. Several soil quality indicators, including the Enrichment Factor (EF), Contamination Factor (CF), Ecological Risk Index (ERI), and Potential Ecological Risk Index (RI), were calculated to determine the quality and pollution levels of the collected soil samples. According to the calculated RI values, 70 out of 77 sites sampled in the area around the HSW are in the “High Risk” class in terms of all studied PTEs. The soil profile samples indicated that the topsoil (0–50 cm) was heavily contaminated by all PTEs, particularly near a zinc processing plant established in 1976. In addition, parts of the wetland further away from the Zn processing plant were also affected by arsenic pollution from geogenic sources, which can be associated with Plio-Quaternary volcanic activity in the region.

  AtıfScopus3·WoS3

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• MakaleYayıncıda açık erişim2023/r/bayburt/12967
  Evaluation of Groundwater Vulnerability in the Upper Kelkit Valley (Northeastern Turkey) Using DRASTIC and AHP-DRASTICLu Models

  Yıldırım, Ümit

  This study aimed to investigate groundwater vulnerability to pollution in the Upper Kelkit Valley (NE Turkey). For this purpose, vulnerability index maps were created using the generic DRASTIC and AHP-DRASTICLu models. The latter model was suggested by adding a parameter to the DRASTIC model and weighting its parameters with the analytical hierarchy process with the GIS technique. The results showed that areas with high and very high vulnerabilities are concentrated around the Kelkit Stream, which flows from east to west in the central part of the study area. In contrast, areas with low and very low vulnerability classes are located in the northern and southern parts of the study area. To validate the model results, a physicochemical characterization of groundwater samples and their corresponding vulnerability index values were statistically compared using the Spearman correlation method. In addition, the single-parameter sensitivity method was applied to analyze the models’ sensitivities. Results revealed a stronger correlation between the vulnerability index values of the AHP-DRASTICLu model (compared to the DRASTIC model) in terms of sulfate (R2 = 0.75) and chloride (R2 = 0.76), while there was a slightly weaker correlation for the electrical conductivity (R2 = 0.65) values of the groundwater samples. Sensitivity analysis indicated that the vadose zone, aquifer media, and land use are the most influential parameters responsible for the highest variation in the vulnerability index. Generally speaking, the results indicated that the AHP-DRASTICLu model performs better than the DRASTIC model for investigating groundwater vulnerability to pollution in the Upper Kelkit Valley.

  AtıfScopus9·WoS5

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• MakaleYayıncıda açık erişim2022/r/bayburt/13194
  Assessment of Climate Change Impact on Discharge of the Lakhmass Catchment (Northwest Tunisia)

  Ben Nsir, Siwar; Jomaa, Seifeddine; Yıldırım, Ümit; Zhou, Xiangqian; D’Oria, Marco; Rode, Michael; Khlifi, Slaheddine

  The Mediterranean region is increasingly recognized as a climate change hotspot but is highly underrepresented in hydrological climate change studies. This study aims to investigate the climate change effects on the hydrology of Lakhmass catchment in Tunisia. Lakhmass catchment is a part of the Medium Valley of Medjerda in northwestern Tunisia that drains an area of 126 km². First, the Hydrologiska Byråns Vattenbalansavdelning light (HBV-light) model was calibrated and validated successfully at a daily time step to simulate discharge during the 1981–1986 period. The Nash Sutcliffe Efficiency and Percent bias (NSE, PBIAS) were (0.80, +2.0%) and (0.53, −9.5%) for calibration (September 1982–August 1984) and validation (September 1984–August 1986) periods, respectively. Second, HBV-light model was considered as a predictive tool to simulate discharge in a baseline period (1981–2009) and future projections using data (precipitation and temperature) from thirteen combinations of General Circulation Models (GCMs) and Regional Climatic Models (RCMs). We used two trajectories of Representative Concentration Pathways, RCP4.5 and RCP8.5, suggested by the Intergovernmental Panel on Climate Change (IPCC). Each RCP is divided into three projection periods: near-term (2010–2039), mid-term (2040–2069) and long-term (2070–2099). For both scenarios, a decrease in precipitation and discharge will be expected with an increase in air temperature and a reduction in precipitation with almost 5% for every +1 °C of global warming. By long-term (2070–2099) projection period, results suggested an increase in temperature with about 2.7 °C and 4 °C, and a decrease in precipitation of approximately 7.5% and 15% under RCP4.5 and RCP8.5, respectively. This will likely result in a reduction of discharge of 12.5% and 36.6% under RCP4.5 and RCP8.5, respectively. This situation calls for early climate change adaptation measures under a participatory approach, including multiple stakeholders and water users.

  AtıfScopus11·WoS11

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• MakaleYalnız künye2021/r/bayburt/14269
  MORPHOMETRIC ANALYSIS TO INFER HYDROLOGICAL BEHAVIOUR OF CORUH RIVER BASIN (NORTHERN TURKEY) USING GIS TECHNIQUE

  Yildirim, Umit

  Morphometric analysis is a very practical approach for evaluating hydrological processes for watersheds. The combination of morphometric, geological, and geomorphological characteristics of the river basin helps to gain further insights in forecasting hydrological phenomena (such as flooding, soil erosion, and groundwater potential). In this study, the morphometric analysis of the Coruh River Basin was conducted using GIS to establish effective water management. Firstly, the basic morphometric parameters (basin area, basin length, basin perimeter, stream order, stream number, and total stream length) were calculated for both CRB and its subbasins. Then, characteristic morphometric parameters (drainage density, drainage texture, form factor, length of the overland flow, topographic wetness index, and stream power index) were determined. Results showed that the infiltration capacity of the subsurface material was low, and the surface runoff was slow in the subbasins located close to the CRB's outlet. Therefore, these subbasins are more sensitive to flooding, erosion, and landslides compared to others. Soil erosion and thus sediment loss is higher in 1st, 2nd, 3rd, and 5th subbasins, and the groundwater potential is higher in headwater areas of the basin. This study revealed that the GIS-based morphometric analysis is beneficial to implement water management tool at the watershed scale.

  AtıfWoS1

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• MakaleYayıncıda açık erişim2021/r/bayburt/13426
  Identification of groundwater potential zones using gis and multi-criteria decision-making techniques: A case study upper coruh river basin (ne Turkey)

  Yıldırım, Ümit

  In this study, geographic information system (GIS)-based, analytic hierarchy process (AHP) techniques were used to identify groundwater potential zones to provide insight to decisionmakers and local authorities for present and future planning. Ten different geo-environmental factors, such as slope, topographic wetness index, geomorphology, drainage density, lithology, lineament density, rainfall, soil type, soil thickness, and land-use classes were selected as the decision criteria, and related GIS tools were used for creating, analysing and standardising the layers. The final groundwater potential zones map was delineated, using the weighted linear combination (WLC) aggregation method. The map was spatially classified into very high potential, high potential, moderate potential, low potential, and very low potential. The results showed that 21.5% of the basin area is characterised by high to very high groundwater potential. In comparison, the very low to low groundwater potential occupies 57.15%, and the moderate groundwater potential covers 21.4% of the basin area. Finally, the GWPZs map was investigated to validate the model, using discharges and depth to groundwater data related to 22 wells scattered over the basin. The validation results showed that GWPZs classes strongly overlap with the well discharges and groundwater depth located in the given area.

  AtıfScopus65·WoS52

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• MakaleYayıncıda açık erişim2021/r/bayburt/13282
  Modelling of the discharge response to climate change under RCP8.5 scenario in the Alata river basin (Mersin, SE Turkey)

  Yıldırım, Ümit; Güler, Cüneyt; Önol, Barış; Rode, Michael; Jomaa, Seifeddine

  This study investigates the impacts of climate change on the hydrological response of a Mediterranean mesoscale catchment using a hydrological model. The effect of climate change on the discharge of the Alata River Basin in Mersin province (Turkey) was assessed under the worstcase climate change scenario (i.e., RCP8.5), using the semi-distributed, process-based hydrological model Hydrological Predictions for the Environment (HYPE). First, the model was evaluated temporally and spatially and has been shown to reproduce the measured discharge consistently. Second, the discharge was predicted under climate projections in three distinct future periods (i.e., 2021–2040, 2046–2065 and 2081–2100, reflecting the beginning, middle and end of the century, respectively). Climate change projections showed that the annual mean temperature in the Alata River Basin rises for the beginning, middle and end of the century, with about 1.35, 2.13 and 4.11 °C, respectively. Besides, the highest discharge timing seems to occur one month earlier (February instead of March) compared to the baseline period (2000–2011) in the beginning and middle of the century. The results show a decrease in precipitation and an increase in temperature in all future projections, resulting in more snowmelt and higher discharge generation in the beginning and middle of the century scenarios. However, at the end of the century, the discharge significantly decreased due to increased evapotranspiration and reduced snow depth in the upstream area. The findings of this study can help develop efficient climate change adaptation options in the Levant’s coastal areas.

  AtıfScopus16

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