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• MakaleYalnız künye2026/r/gumushane/13675
  The Trend of Monthly Mean Streamflow Values and Regimes in the Susurluk Basin (Türkiye) with Mountain and Semi-Arid Climates

  Yıldız, Mehmet Berkant; Toğrul, Burçe; Kankal, Murat; Akçay, Fatma; Şan, Murat; Nacar, Sinan

  This study diagnoses monthly trends in streamflow magnitude and regime for the Susurluk Basin (Türkiye), which spans semi-arid and mountainous sub-climates. Monthly records from 1990 to 2019 were analyzed at 14 stream gauges and nine precipitation stations. Trends are assessed with the Mann–Kendall (MK) test alongside recent graphical approaches, Improved Visualization for Innovative Trend Analyses (IV-ITA) to resolve value class-based (low/high) behavior, and Innovative Polygon Trend Analysis (IPTA) with the Star Concept to quantify intra-annual transitions. Before the trend analyses, the stations were tested to determine whether their values were homogeneous, and any inhomogeneous stations were excluded from the study. The consistency between the trends of nine precipitation stations and the streamflow data in the basin was analyzed. Across the basin, the average streamflow increased by approximately 40–60% between January and March at many measurement points. However, it then decreased by around 80% in April, albeit at a more moderate rate in December. This suggests significant rebalancing occurred during the December–April period, when most of the annual streamflow occurs. IV-ITA exhibits broadly similar trends for both low and high streamflow classes, with notable exceptions in January–February. Precipitation–streamflow trend directions are largely consistent in the high-flow season (December–April), supporting the notion that climatic control influences the detected shifts. To contextualize these signals, basin-wide land-use/land-cover shifts (1990–2018), notably urban growth, forest expansion, and cropland reconfiguration, provide process context, indicating that a larger fraction of rainfall is routed as fast surface runoff while infiltration and base streamflow recharge decline, alongside seasonally modified water demand. Collectively, the MK+IV-ITA+IPTA framework reveals class-specific and intra-annual dynamics that are obscured by monolithic tests alone and provides decision-relevant evidence for allocation, drought–flood risk, and operations in an intensively managed basin.

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• MakaleAçık Erişim2026/r/gumushane/13580
  Development of the seasonal non-monotonic Mann-Kendall test for hydroclimatic data

  Şan, Murat

  Climate change can show different characteristics at low and high values of a time series, leading to non-monotonic trends. The Mann-Kendall (MK) and seasonal MK tests can only detect monotonic trends and ignore different behaviors in low and high value groups. To overcome this limitation, extending the recently proposed non-monotonic MK (NMK) test, the seasonal NMK (SNMK) test is proposed. The method was applied to four stations in Türkiye with four different climatic and topographic characteristics using monthly total precipitation data for the 1969-2020 for seasonal trend behavior. The results showed that while no significant trends were detected in entire time series, intra-seasonal and annual data, both monotonic and non-monotonic significant trends emerged in seasonal analyses. Especially in two stations, opposite changes in low and high values, increased seasonal variance and non-monotonic seasonal trends were observed. The test can be used for regional trend analysis by replacing seasonal data with regional data. It is also predicted that the SNMK test can be used as an effective decision support tool in areas with high seasonality such as water resources management, agriculture, energy planning and disaster management.

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• MakaleYalnız künye2026/r/gumushane/12318
  Analysis of the Changes in River Water Quality and Quantity with Innovative Trend Methods

  Şan, Murat; Nacar, Sinan; Bayram, Adem; Kankal, Murat

  This study aims to investigate trends and changes in water quality (WQ) and quantity parameters under low-medium-high groups and seasonal trends employing innovative methods. The data were collected from three monitoring stations in the Broad River Basin (USA). The data spanning the years 1987–2020, on water temperature (WT), dissolved oxygen (DO), discharge (Q), and electrical conductivity (EC) parameters, were used for analysis. A combination of innovative trend analysis with binary segmentation (ITABS) was proposed for objective group separation for the purpose of group trend analysis, allowing for the capture of changes in both location and shape parameters. Recently proposed innovative polygon trend Wilcoxon significance test (IPTWST) and innovative polygon trend analysis (IPTA) were also used to examine seasonal trends for the first time, providing a graphical and qualitative analysis of seasonal behavior. The seasonal Mann-Kendall test was also used to compare them. The ITABS method grouped WQ parameters into more than one group, except for the DO parameter. Especially from EC and Q parameters, it is concluded that the trends in groups do not always contribute to the overall trend or at the same rate. Group trends, therefore, should not be ignored for water resources management. According to IPTA and IPTWST, although there is no clear trend in certain seasons, it is evident that seasonal trends exist, and the Q and EC parameters have a more complex structure. The IPTWST method has the advantage of being able to graphically show the inter-seasonal behavior, although it is identical to the seasonal Mann-Kendall method.

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• MakaleYalnız künye2026/r/gumushane/12204
  Monthly precipitation trends in Türkiye under complex topography and varying climate: a seasonal Mann–Kendall and innovative polygon trend framework

  Şan, Murat; Nacar, Sinan; Kankal, Murat

  The impacts of climate change are increasingly sensible, and Türkiye with its varied topography and diverse climate types is particularly exposed to these shifts. Understanding how precipitation patterns are evolving across its regions is therefore critical. While trend analysis is a widely used tool for this purpose, conventional approaches overlook periodicity, limiting their practical value for water resource management and irrigated agriculture. Therefore, this study aims to examine seasonal trends in long-term (1969–2020) monthly total precipitation in Türkiye, in which each calendar month is treated as a separate season in the sense of seasonal trend-analysis terminology, accounting for altitude, slope, geographical region, and Köppen climate classification. For this purpose, the seasonal Mann-Kendall (SMK) test and the innovative polygon trend Wilcoxon significance test (IPWST), a relatively new graphical method, were used, and the two approaches were comparatively evaluated. According to the study’s results, the rate of increase in coastal areas, specifically the Aegean and Black Seas, exceeds the rate of decrease. In contrast, the reverse is observed in inland and eastern regions. The IPTWST method indicates a more pronounced increasing trend in the Marmara and Mediterranean regions. Furthermore, although analogous trends are observed at lower slopes and altitudes, analyses indicate that these trends are more strongly related to altitude, with the rate of increase decreasing as altitude increases. The IPTWST identified significant or weak trend signals at a larger number of stations than the SMK, particularly in relation to altitude. Nationwide, the two methods revealed significant increases of 7% and decreases of 6%, respectively; this pattern was supported by statistical tests, reflecting the variability of regional climates and the influence of topographic factors on trend analysis.

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• MakaleYalnız künye2026/r/gumushane/12112
  Stationarity or nonlinear nonstationarity? Assessing standard duration extreme rainfall under Türkiye’s complex topography and climate variability

  Şahin, Nagehan; Şan, Murat; Kankal, Murat

  The impact of climate change on extreme rainfall regimes requires a reassessment of the design processes of traditional hydrological structures. For this purpose, conducting an in-depth analysis of the nonstationary nature of extreme rainfall in regions with complex topography and climate is of great importance. This study examines the stationary and nonstationary states of standard duration (5 min–24 h) annual maximum rainfall data across Türkiye. For this purpose, the intensity-duration-frequency relationship was analyzed using data at 100 homogeneous stations during 1980–2020. The analyses were performed using the generalized extreme value (GEV) distribution with eight linear and non linear location and scale parameters, based on stationary and nonstationary models. Time was included as a covariate in nonstationary models. The corrected akaike information criterion and likelihood ratio test were used to select the appropriate GEV distribution. Findings indicate that stationarity is generally dominant, but nonstationarity is relatively higher in a nonlinear manner in cold climates and complex topography. The effect of location and scale parameters was found to be individual in the short duration and combined in the long duration. It was observed that nonstationarity was relatively higher in complex topography than in flatter regions up to 8 h. Still, the diversity of nonlinear models decreased over the long duration. In conclusion, this study emphasizes the need to consider nonstationary approaches in designing hydrological structures, especially in climate change.

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• MakaleAçık Erişim2025/r/gumushane/19703
  Seasonal Wilcoxon and Scatter Diagram Combination Trend Test

  Şan, Murat

  Climate change, one of the biggest problems of the last century, is of great concern. It is essential and common to examine the impacts of climate change as a holistic trend for different climatic and hydrological parameters with periodicity. However, considering the periodicity character of monthly, weekly, etc., is particularly important for analyzing and understanding seasonal trends. This is because seasonal trends help manage and regulate irrigation and agricultural activities and water resource systems. This study proposes the seasonal Wilcoxon and scatter diagram combination trend test (SWTT) method as an alternative to the seasonal Mann Kendall (SMK) method. This method is based on the combination Wilcoxon test and scatter diagram (CWTSD) trend test which assesses holistic trends. The data utilized for this study came from three sources: flow records from the Danube River, Romania, temperature records from Oxford, UK, and precipitation records from Kobe, Japan, to compare SWTT and SMK methods. The SWTT method shows very similar trends to the SMK, but the SWTT method takes a step forward because it is based on a graphical method providing a visual overview of seasonal trends. The SWTT can also be used as a regional trend test in the same way that the SMK method is used as a regional trend test by using station data instead of seasons The r-codes of the proposed method and the sample dataset are available at the related link.

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• MakaleYalnız künye2025/r/gumushane/12505
  Spatial and temporal patterns of drought under different scenarios for Türkiye in the 21st century

  Yıldız, Mehmet Berkant; Nacar, Sinan; Şan, Murat; Kankal, Murat

  This study investigates the impact of climate change on drought conditions in Türkiye for two distinct future periods: the near future (2021–2050) and the far future (2071–2100), under two emission scenarios (RCP4.5 and RCP8.5). High-resolution regional climate projections from 19 GCM-RCM combinations within the EURO-CORDEX framework were evaluated. Based on performance analysis against ERA5-Land data, the four best-performing models were selected for multi-model ensemble averaging (MMEA). Drought conditions were assessed using the Standardized Precipitation Index (SPI) at 3-, 6-, and 12-month time scales. Three trend analysis methods, Innovative Trend Analysis (ITA), Modified Mann-Kendall (MMK), and Sen's Slope, were applied to examine spatiotemporal drought patterns. SPI-based analyses show a significant increase in short- and medium-term variability (SPI-3 and SPI-6) and long-term droughts (SPI-12), especially in the Central Anatolia, Southeastern and Eastern regions. The applied trend detection methods consistently point to a widespread drying tendency, with more pronounced changes projected in the latter half of the century. Under the RCP4.5 scenario, although the drought signals are less severe, the persistence of negative trends highlights that Türkiye will still be at risk, even with moderate efforts to mitigate climate change. These findings underscore the urgent need for integrating climate-driven drought projections into national and regional planning efforts.

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• MakaleAçık Erişim2025/r/gumushane/12490
  Combined innovative trend analysis methods for seasonal trend testing

  Şan, Murat

  While holistic trend identification is essential, it does not consider the periodic, e.g., monthly, trend characteristics needed to identify seasonal trend behavior. Furthermore, identifying seasonal trends can help manage or regulate water resources systems and irrigation and agricultural operations. In this study, the innovative trend significance test (ITST), the revised ITST, and the Wilcoxon signed-rank test, which are non-parametric methods, are proposed as alternative seasonal trend tests by combining them with the innovative polygon trend analysis (IPTA), which provides visual and linguistic examinations of seasonal behaviors. Groundwater level data from the Chilgrove House (United Kingdom), flow data from the Danube River Basin (Romania), precipitation and temperature data from Türkiye were used to compare the proposed methods with the seasonal Mann-Kendall (SMK) method. For temperature and groundwater level data, all methods showed an increasing trend at different confidence intervals, but for other data, trends emerged according to the characteristics of the methods. So, some of the proposed methods are more rigid than the SMK in trend detection, while others are more sensitive. In addition to the advantage of its applications to seasonal trend behaviors, the proposed significance tests are combined with the IPTA method and comparable alternative methods to the SMK. So, seasons with a clear increase or decrease can be seen visually in the proposed combined methods contrary to the SMK method. Thus, both seasonal trend behaviors and inter-seasonal transitions can be examined graphically, and seasonal significance testing can be applied. According to the characteristics of these combined methods, they can be used not only for seasonal trend tests, just like the SMK method, but also for regional trend tests using stations data instead of seasons.

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• MakaleYalnız künye2025/r/gumushane/12374
  Analysis of drought in upper Moulouya Basin (Morocco): a combination of drought indices, classic and innovative trend tests

  Qadem, Zohair; Hadria, Rachid; Ettaqy, Abderrahim; Kankal, Murat; Şan, Murat; Nacar, Sinan

  This study aimed to examine the temporal and spatial variation of drought in the upper Moulouya Basin, Morocco’s arid and semi-arid region. For this purpose, the Standardized Precipitation Index (SPI) was calculated at various time scales (3, 6, 12, and 24 months) using precipitation data collected from eight stations between 1977 and 2019. The data trends were analysed by classical modified Mann-Kendall (MMK) and Innovative Trend Analysis (ITA). Severe drought events were identified in the 1980s, and 1998–2000, while exceptionally wet years were recorded in periods 1996–1997 and 2008–2012. SPI trend analyses revealed a holistic increase on almost all timescales and at all stations. The increase was found to be higher in more extended time scales. Except for a few stations, SPI values in dry, normal, and wet classes of ITA method increased in the second half (1998–2019) compared to the first half (1978–1997). The ITA method detected different trends for different classes at two stations compared to the MMK method. This situation revealed the importance of analysing the trends of different methods in drought studies. These results are essential for water resources management and adaptation to climate change in arid and semi-arid zones.

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• MakaleYalnız künye2024/r/gumushane/14440
  Innovative Polygonal Trend Analysis (IPTA) in detecting the seasonal trend behavior of statistically downscaled precipitation for the Eastern Black Sea Basin of Turkey

  Nacar, Sinan; Şan, Murat; Kankal, Murat; Okkan, Umut

  This study compares projected and past seasonal precipitation trends in the Eastern Black Sea Basin, Turkey. Historical data from twelve stations representing the basin during 1981–2010 was used, while statistically downscaled data from two representative concentration pathway scenarios (RCP4.5 and RCP8.5) outputs of the GFDL-ESM2M general circulation model were utilized for 2021–2050. To determine the seasonal trend behaviors of precipitation variables and transitions between consecutive months, the Innovative Polygon Trend Analysis (IPTA) was implemented. Furthermore, the star concept was employed to illustrate the changing sizes between consecutive periods. Both scenarios showed considerable summer and autumn declines at almost all locations, with low seasonal precipitation variability. These scenarios indicated January to be the important month for trend shift, except for Rize, Pazar, and Hopa stations. The formation of several polygons, polygons intersecting, and polygons not forming on the global regression line show that the hydro-climatic cycle might be chaotic.

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