Person: AKBAŞ, ABDULLAH
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AKBAŞ
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ABDULLAH
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Publication The effects of spatial resolution variability of digital elevation models on flood hazard analysis(Istanbul Univ, Fac Letters, Dept Geography, 2023-01-01) Özdemir, Hasan; ÖZDEMİR, HASAN; Akbaş, Abdullah; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0001-8885-9298; 0000-0003-2024-0565; Y-4236-2018; AAI-6814-2021Raster-based Digital Elevation Models (DEMs) represent the surface topography as the primary input in flood hazard and risk studies. The study aims to reveal the variability of the hazard at the base of the Ulus settlement by performing flood hazard analyses with different source and resolution DEMs, which are used on a global and local scale and form a primary input for many studies. For this purpose, DEMs data, such as MERIT 90m, FABDEM 30m, TopoDEM 10m, DEM5m, LiDAR 1m, and UAV 0.1m, for the Ulus River basin and settlement and the 500-year flood produced for the river tributaries using the SWAT rainfall-runoff model were used. To examine spatial resolution variability, flood hazard analyses were performed based on the two-dimensional LISFLOOD-FP hydrodynamic model, using a fixed Manning n value (n=0.035). As a result, although there is an increase in cost, time, and model instabilities from low resolution to high resolution, it is essential to choose the most appropriate DEM according to the required detail and scale of the hazard analysis to be able to obtain more accurate results. While the model time and average computational errors from low resolution to high resolution increased, the water extent and the spatial distribution of the hazard classes produced for people and buildings decreased. The FABDEM data is more advantageous in regional studies than others, whereas the LiDAR data can be used in basin-scaled studies. In addition, the DEM5 data also can be used in basin-scaled studies after clearing the heights of the buildings and vegetation groups.Publication Regional distribution and characteristics of major badland landscapes in Turkey(Elsevier, 2022-08-24) Avcıoğlu, Aydoğan; Görüm, Tolga; Akbaş, Abdullah; Moreno-de las Heras, Mariano; Yıldırım, Cengiz; Yetemen, Ömer; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0003-2024-0565; AAI-6814-2021Badlands are extremely rugged, outstanding landscapes that can be seen in all ice-free climate regions over erosion-susceptible unconsolidated materials, and they have drawn attention with their spectacular and iconic forms. Unlike nearly all badlands researches conducted at the experimental site and watershed scale, so far, the broader-scale evaluation has been neglected in the analysis of badland distribution, characteristics, and dynamics. Our study provides an integrative new insight into badland landscapes by investigating the distribution, characteristics and controlling factors of Turkish badlands on a broad, regional scale. We inventoried Turkish badlands using aerial imagery and studied their distribution using K-means clustering, an unsupervised machine learning algorithm, based on a set of major conditional geo-environmental factors that control the regional distribution and characteristics of badlands, including tectonics, lithology, topography, climate, and vegetation. Here, we identified, a total of 4494 km(2) of badland areas which are non-uniformly distributed across Turkey, substantially clustered in the Central Anatolian Plateau (CAP). According to our regional analyses, we have determined a total of five badland regions comprising three major types classified as Semi-arid, Mediterranean, and Montane (humid), together with two transitional types in-between the Semi-arid and Montane badland regions. Our results indicate that temperature seasonality (0.83), mean annual precipitation (0.83), and precipitation seasonality (0.76) are predominantly assigned to the badlands clusters. The clastic rocks are revealed as the most crucial and inevitable factor for the development of Turkish badlands, which are represented in a wide geologic time-scale (Cretaceous to Quaternary) and diverse lithological units (i.e., lacustrine, volcaniclastics, and terrestrial). Neogene and Paleogene terrestrial clastics (77 %) constitute the majority of the litho-logic settings of these badland landscapes. The active and complex tectonic history of Turkey has portrayed the fundamental frame of the identified badland regions, by providing a susceptible environment (i.e., development of sedimentary basins) and promoting badland development through successive base-level changes. Furthermore, tectonically-modulated (i.e., formation of orogenic belts, and uplifting of CAP) climate dynamics outline the distribution pattern and differentiation of the regional characteristics of badlands in Turkey. Overall, our regional-scale approach to badland mapping and regional synthesis may decipher not only the tectonic and climatic conditions of the identified badlands regions, but it may also contribute to the implementation of future effective strategies for the detection and mapping of erosion susceptible and high sediment flux areas in very broad spatial contexts of similar unexplored territories.Publication Is there a consistency in basin morphometry and hydrodynamic modelling results in terms of the flood generation potential of basins? A case study from the ulus river basin (Turkiye)(Elsevier, 2023-08-02) Özdemir, Hasan; Akbaş, Abdullah; ÖZDEMİR, HASAN; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Fiziki Coğrafya Ana Bilim Dalı; Coğrafya Bölümü; 0000-0001-8885-9298; 0000-0003-2024-0565; AAI-6814-2021; Y-4236-2018Floods are natural phenomena that increase their impact every year due to increasing natural and anthropogenic variables, which are effective individually or together. Many research studies have focused on understanding the causative factors. This study aims to reveal whether there is a consistency in the results of the basin morphometry and hydrodynamic model used to understand the flood generation potential of river basins. Both analyses have been discussed individually in many papers but are not comprehensively compared. The Ulus settlement (Turkiye), where Ulus upstream, Suleyman, Alpi, and Eldes tributaries converge, was chosen as a study area. The results of the two analyses were evaluated in terms of their potential ability to produce floods over the subbasins and the Ulus settlement. Eight basin morphometric parameters were applied to the 10 m resolution TopoDEM data, and the results were evaluated according to the Normalised Morphometric Flood Index (NMFI) method, which helps decrease subjectivity in ranking the results. Flow data of the ungauged subbasins were produced using the SWAT rainfall-runoff model, and 2, 5, 10, 20, 50, 100, 200, 500, and 1000 years maximum flow data were generated using flood frequency analysis, and the different flow data were modelled based on 1 m LiDAR DEM using the LISFLOOD-FP 2D-hydrodynamic model. According to the results, the Suleyman subbasin has the highest flood generation potential in basin morphometry and hydrodynamic modelling. It is followed by the Alpi subbasin at high potential, Ulus upstream and Eldes subbasins at medium potential. As a result, we determine there is a consistency in basin morphometry and hydrodynamic modelling results. The basin morphometry and the developed NMFI can be used to determine and understand the flood-generating potential of basins or subbasins in data-scarce regions regarding flood modelling.Publication Influence of atmospheric circulation on the variability of hydroclimatic parameters in the Marmara Sea river basins(Taylor, 2023-06-02) Akbaş, Abdullah; Özdemir, Hasan; AKBAŞ, ABDULLAH; ÖZDEMİR, HASAN; Fen Edebiyat Fakültesi,; Fiziki Coğrafya Ana Bilim Dalı; Coğrafya Bölümü; 0000-0003-2024-0565; 0000-0001-8885-9298; AAI-6814-2021; Y-4236-2018Understanding the influence of atmospheric circulation on the variability of hydroclimatic parameters can considerably contribute to water management. In this study, atmospheric dynamics on rainfall/runoff variability in Marmara Sea river basins were investigated via principal component analysis (PCA) and trend analyses. Correlation maps were obtained for rainfall/runoff PC scores and 500 hPa geopotential using ECMWF Reanalysis v5 (ERA5). The correlations between rainfall/runoff PC scores and teleconnection indices were employed to support the PCA analysis. The first component, a monopolar structure, expresses northerly atmospheric influence on the rainfall/runoff; the second component, a dipolar structure, explains the low rainfall/runoff conditions; the last component defines local properties. Teleconnections demonstrate that North Atlantic Oscillation (NAO) is highly correlated with rainfall and runoff PC scores, particularly in winter. Moreover, runoff trends are consistent with rainfall trends except for summer, and these trends and oscillations are related to the teleconnections. Therefore, the anomalies can be predicted based on atmospheric conditions.Publication Multi-proxy sedimentary records of dry-wet climate cycles during the last 2 ka from lake cildir, east anatolian plateau, Turkey(Comitato Glaciologico Italiano, 2019-01-01) Erginal, Ahmet Evren; Çagatay, M. Namık; Selim, H. Haluk; Çakır, Cağlar; Yakupoğlu, Nurettin; Acar, Dursun; Kaya, Hakan; Karabıyıkoğlu, Mustafa; Akbas, Abdullah; AKBAŞ, ABDULLAH; Bursa Uludağ Üniversitesi; 0000-0003-2024-0565; AAI-6814-2021Multi-proxy analyses together with AMS radiocarbon dating of sedimentary organic carbon of a sediment core from Lake Cildir, NE Turkey was carried out to study temporal changes in climate over the last two millennia. The lake is characterized by very fine to coarse silt-sized, carbonate-free sediments deposited at a relatively low sedimentation rate of less than 0.31 mm/yr. Results from element geochemistry, total organic carbon (C-org), and physical properties (gamma density and magnetic susceptibility results testified the occurrence of alternating cycles of drier and wetter climatic periods since about 2.2 ka cal BP. The period from 2166 +/- 112 cal BP to the onset of Little Ice Age, including the Medieval Climatic Anomaly, is represented by alternation of warm and wet conditions with intervening relatively low-magnitude dry periods. The cold Little Ice Age period, on the other hand, was dry, with upward decreasing trends of Zr and Ti and C-org as well as relatively low values of Rb/Sr, indicating decreasing chemical weathering intensity in the drainage basin and low organic productivity in the lake.Publication Termination of little ice age in Northeastern Anatolia: A multi-proxy paleolimnology study of lake aygir sediments, (Kars, ne Anatolia)(Tmmob Jeoloji Muhendisleri Odasi, 2022-04-01) Erginal, Ahmet Evren; Yakupoğlu, Nurettin; Çakır, Çağlar; Kükrer, Serkan; Akbaş, Abdullah; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0003-2024-0565; AAI-6814-2021Sedimentary, geochemical and stable isotope analyses of a sediment core (core AY) recovered from Lake Aygir (NE Anatolia) provide evidence of the climatic shifts during the last similar to 500 yrs. Sediments in Lake Aygir are composed of silty clay with a modeled similar to 0.16 cm/yr sedimentation rate. Multi-proxy analyses of the downcore distribution of detritally-deposited proxy elements, total calcium carbonate, organic carbon and stable isotopes reveal climatic records of the Industrial Epoch (IE; 18th-19th centuries) and the termination of the Little Ice Age (LIA; AD 1350 to 1850), represented by fluctuating Total Organic Carbon (TOC), Ca, Sr and relatively low detrital precursors (Fe, Ti, K, Rb, Zr), indicating low chemical weathering and dry conditions. The upper part of the core (192 cal yrs BP to present), identified with high detrital input, contains an increasing trend of Fe, Ti, K, Rb, and Zr together with high delta O-18 and delta C-13 values, indicating warmer conditions during the IE.Publication Human or climate? differentiating the anthropogenic and climatic drivers of lake storage changes on spatial perspective via remote sensing data(Elsevier, 2023-12-05) Akbaş, Abdullah; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0003-2024-0565; AAI-6814-2021Lakes are an essential part of the terrestrial water system in which storage changes are controlled by water balance and human impact. Although there are some attempts to define storage changes on a global scale, ex-amination of spatial relations is poorly quantified. In this study, therefore, lake storage changes have been investigated using remote-sensing-derived data around the globe. Hence, 372 artificial/natural lakes were obtained, covering between 1992 and 2019. Watersheds belong to river was extracted via HydroSHED data. Based on watershed, dominant climate types were determined via Ko center dot ppen-Geiger classification. Similarly, the areal average CRU TS v.4.05 monthly gridded precipitation time series and human footprint data based on watersheds were obtained to understand the drivers of lake storage changes. The nonparametric Mann-Kendall and Sen's slope trend analyses were applied to the lake storage change and precipiation values in order to determine long-term increases and decreases. A bivariate map was constructed between storage changes trend vs precipitation trend and human footprint to reveal the drivers of lake storage changes in terms of spatial aspects. The trend analysis and bivariate map results show that North America, the East African Highlands, and the Tibet plateau are important increasing hotspots, where precipitation is a significant driver for storage oscillations, except for the Tibet plateau. Besides, the Brazilian Highlands, Pacific Mountain System, and Intermontane of conterminous USA are other decreasing hotspots in which human footprint and decreasing precipitation collectively affect these changes. Furthermore, results clearly show that anthropogenic influence is low in the northern and mountainous areas, and storage changes have a linear relationship with precipitation. In contrast, intense human climate interaction influences lake changes in plains areas and arid/temperate climates.Publication All models are wrong, but some are useful: Determining the low (drought) and high (flood) flow characteristics in ungauged basins(İstanbul Üniversitesi, 2022-01-01) Akbaş, Abdullah; Özdemir, Hasan; AKBAŞ, ABDULLAH; ÖZDEMİR, HASAN; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0003-2024-0565; 0000-0001-8885-9298; AAI-6814-2021; Y-4236-2018Although instrumental observations in basins are essential for understanding basin processes, acquiring observational data from all locations is challenging. Therefore, this study aims to simulate low and high flows and compare them with observations. With this aim, 90 sub-basins were generated, and hydrological response units (HRUs) were obtained by overlaying data such as land use, slope, and soil. Hydrological processes were simulated based on water balance using meteorological data within the basin and the HRUs. The model results were used for calibration by means of the SWAT-CUP using data from station E13A031. The modeled results that were obtained for simulating basin processes are considered sufficient. The different time series characteristics (i.e., magnitude, frequency, duration, and timing) belonging to low and high flow characteristics have been estimated and compared with the observed data. Even though good coherence was present between the observed and modeled low/high flow metrics, many sources of uncertainty exist that caused over-and under-estimations regarding some metrics. Furthermore, the metrics for all sub-basins have been calculated. According to the results, the Kocanaz basin reflects high differences in the metrics for low and high flows compared to the other basins. In this context, hydrological models offer opportunities for planning and watershed management in order for understanding climate and land-use changes.Publication The effect of post-wildfire management practices on vegetation recovery: Insights from the sapadere fire, Antalya, Turkiye(Frontiers Media Sa, 2023-04-07) Yıldız, Cihan; Comert, Resul; Tanyas, Hakan; Yılmaz, Abdussamet; Akbaş, Abdullah; Akay, Semih Sami; Yetemen, Ömer; Görüm, Tolga; AKBAŞ, ABDULLAH; Fen Edebiyat Fakültesi; Coğrafya Bölümü; 0000-0003-2024-0565; AAI-6814-2021Post-wildfire management actions mainly targeting the removal of salvage logs and burned trees is a common but controversial practice. Although it aims to regain some of the natural and economic value of a forest, it also requires disturbing burned areas, which may have some negative consequences affecting, for instance, the carbon cycle, soil erosion, and vegetation cover. Observations from different geographic settings contribute to this scientific debate, and yet, the spatiotemporal evolution of the post-fire road network developed as part of fire management practices and its influence on vegetation recovery has been rarely examined. Specifically, we still lack observations from Turkiye, though wildfires are a common event. This research examined the evolution of the vegetation cover in relation to post-fire road constructions and the resultant debris materials in areas affected by the 2017 Sapadere fire in Antalya, Turkiye. We used multi-sensor, multi-temporal optical satellite data and monitored the variation in both vegetation cover and road network from the pre-to post-fire periods between 2014 and 2021. Our results showed that fire management practices almost doubled the road network in the post-fire period, from 487 km to 900 km. Overall, 7% of the burned area was affected by these practices. As a result, vegetation cover in those areas shows only similar to 50% recovery, whereas undisturbed areas exhibit similar to 100% recovery 5 years after the event. Notably, such spatiotemporal analysis carried out for different burned areas would provide a better insight into the most suitable post-fire management practices. Our findings, in particular, show that the current practices need to be revisited as they cause a delay in vegetation recovery.Publication Seasonality, persistency, regionalization, and control mechanism of extreme rainfall over complex terrain(Springer Wien, 2023-04-04) Akbaş, Abdullah; AKBAŞ, ABDULLAH; Bursa Uludağ Üniversitesi; 0000-0003-2024-0565; AAI-6814-2021Extreme rainfall has enormous importance in hazard management as well as the design of critical infrastructures for urban and rural areas. Also, complex terrain has a vast influence on spatial and temporal patterns of extreme rainfall. In this study, therefore, many different properties such as spatial similarity (regionalization) and temporal variability (trends and seasonality) of extreme rainfall were quantified over Turkey in which topography heavily influences meteorological parameters in short distances due to orientation and height of mountain chains. Moreover, spatial and temporal extreme rainfall characteristics are poorly quantified and investigated in Turkey. Principal component analyses (PCA) were used in order to reveal the parameters that have influence on rainfall, and three components were observed based on Kaiser Rule. The three PC explain the effect of topography, large-scale weather systems, and seasonality on extreme rainfall. Model-based clustering via retained component scores were used to generate the extreme rainfall regions. Eight different extreme rainfall regions have been obtained with different return periods and growth curves calculated based on regional frequency analysis via generalized extreme values distribution (GEV) distribution based on the goodness-of-fit measure. SWM (Southwest Mediterranean) and HEBS (Humid Eastern Black Sea) are remarkable regions than other extreme rainfall regions in terms of the magnitude of extreme rainfall because of the interaction of topography with tracks of weather systems. The circular statistic shows a strong gradient in terms of extreme rainfall seasonality between the coastal and interior parts of Anatolia. Moreover, positive trends and persistence in extreme rainfall have been detected in all regions as a signal of the increase in natural hazards. In general, orographic barriers and their interaction with large-scale weather systems shape the spatiotemporal variability of extreme rainfall and creating a negative gradient between interior and frontal parts of the Anatolian plateau.