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The effects of global warming and climate change appear as increasing or decreasing trends in hydrometeorological records in different locations. Identifying trends in long-term (more than 30 year) data is possible through a variety of methodologies as well as classical Mann–Kendall (MK), Regression (R), Spearman's Rho (SR) methods in addition to the innovative trend analysis (ITA) approaches. The most used method in the literature is the MK trend determination test, but it has limited assumptions, and the trend slope is calculated according to Sen's median procedure. However, Sen's approach is an empirical methodology that considers a single median slope from all possible consecutive lag slopes. This paper provides the theoretical probability distribution function (PDF) that matches Sen's slopes, and an innovative probabilistic trend slope methodology is proposed with a set of slope risk levels, rather than statistical slope calculation. The application of the proposed methodology is presented for long-term Danube River annual discharge data in Romania and precipitation records at Antalya resort center in the south along the Mediterranean coast of Turkey. A set of trend lines, objectively different risk levels, are obtained. It has been determined that there are decreasing and increasing monotonic trends in each historical time series record. Therefore, for extreme events, it is possible to consider a particular risk level trend characteristic, i.e., floods and droughts, rather than the classical mean or median level trend definition. [ABSTRACT FROM AUTHOR]

The wind has considerable effects on the ecosystem and evaporation as an essential parameter of the hydrological cycle. Therefore, determining historical changes in the wind will help to specify these effect levels. Although there are studies on the determination of wind speed trends by several researchers in Turkey, it is necessary to investigate the changes in the trend structure with recent data. For this purpose, the trends of monthly surface wind speed data from 1970 to 2021 belonging to 199 meteorology observation stations in Turkey are determined in the present study. The nonparametric Mann–Kendall test and Sen's slope method are used in the trend analysis accounting for serial correlation effects. The trend analysis results of wind speed data are evaluated temporally and spatially for seven geographical regions within Turkey. As a result of this study, a prominent part of stations in Turkey shows a decrease or significant decrease trend. In addition, as a result of comparisons made with previous studies, it is determined that the trend structure of the wind speed in the country has changed. In the annual and monthly wind speeds, it is observed that the number of stations has a "significant trend" decreased considerably. [ABSTRACT FROM AUTHOR]

Drought is a natural disaster that can have devastating economic, environmental, and social impacts on a global, national, and regional scale. Remote sensing technology is the most powerful tool to determine of drought categories and analyse drought severity, vulnerability and its trends. Because data that is temporal, quick, wide-area, and repeating can be obtained via remote sensing technologies. The calculation of drought indices with the use of remote sensing technology is crucial for assessing the severity of the drought and its evolution over time. In this study, the Central Anatolian Basin, one of Turkey's agricultural basins, was subjected to a temporal and spatial drought analysis between 2000 and 2023. In order to analyze the agricultural drought in the Central Anatolian Basin, drought indices such as Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Normalized Difference Drought Index (NDDI), Vegetation Condition Index (VCI), Temperature condition index (TCI), Vegetation Health Index (VHI), Precipitation Condition Index (PCI), and Scaled Drought Condition Index (SDCI) were calculated. Moderate resolution Imaging Spectroradiometer (MODIS) data collection were used to calculate the NDVI, NDWI, NDDI VCI and TCI drought indices and PCI was calculated using the Climate Hazards Group Infrared Precipitation with Station CHIRPS data set. With the results obtained, the change in drought severity in the Central Anatolian Basin over the years was observed and drought severity, plant health status and surface temperature were compared. Additionally Temporal trend and Spatial trend of agricultural drought were determine using Sen's slope and The Mann – Kendal non parametric test. [ABSTRACT FROM AUTHOR]

Water is one of the most essential elements for human life and must be provided for life necessities. Historical changes in hydro-meteorological data are vital for operating and planning water structures. Drought indices are commonly used in the literature to assess the drought. Long-term streamflow records were used to evaluate the hydrological drought based on the Stream Flow Drought Index (SDI) in Sakarya, Kızılırmak and Yeşilırmak basins located in Turkey for 56 years (1965–2020) with sixteen stations. SDI values were calculated at 1-, 3-, 6-, and 12-month scales based on moving averages (MA) to analyze the drought. Run Test and Double Mass Curve were applied to analyze the streamflow data. Moreover, Sen's Innovative Trend Detection Test (SITDT), Innovative Polygon Trend Analysis (IPTA), Mann–Kendall and Sen's slope were applied to evaluate the trend in the streamflow. Findings show that similar results were obtained for SDI-1, SDI-3, SDI-6, and SDI-12 results based on MA at the same stations. Although different droughts occurred, normal droughts were observed more. Downward trends were detected in streamflow data based on IPTA, SITDT, Mann–Kendall and Sen's slope. As a result, assessment of hydrological drought and trend analysis in these basins will contribute to water resources planning and management in the basins. [ABSTRACT FROM AUTHOR]

Knowledge of the historical changes in streamflow is essential for operating and planning water structures. Hence, the monthly mean streamflow trends of 20 streamflow gauge stations in Turkey's Mediterranean basins, which are sensitive to climate change, are examined using the Mann–Kendall test, and trend slopes are calculated using Sen's slope method. Furthermore, the innovative trend significance test (ITST) and recently proposed innovative polygon trend analysis (IPTA) method are used to analyse the historical changes in streamflow values at the stations. The trend analysis results of a total of 240-time series between 1977 and 2015 are evaluated and compared with three different trend methods. As a result of the study, the MK method determined significant trends in only 24% (3 increasing, 55 decreasing), ITST in 83% (41 increasing, 158 decreasing), and IPTA in 82% (38 increasing, 158 decreasing) of the 240-time series. The IPTA and ITST methods are more sensitive to determining significant monthly streamflow trends than the MK method. In addition, there is a more significant decrease in the streamflow values of the stations located east of the basin, and the trend slope value reaches − 26%/decade. Therefore, the results of the streamflow trend in the Mediterranean basins will benefit decision-makers in planning the efficient use of water resources in the region. [ABSTRACT FROM AUTHOR]

The division and evaluation of data series used in monitoring drought into different time intervals is a practical approach to detecting the spatial and temporal extent of drought spread. This study aimed to determine meteorological drought's spatial and temporal distribution using overlapping and consecutive periods and cycles of the standardized precipitation index (SPI) time series in the Mediterranean region, Turkey. In the scope of the research, SPI values for the SPI12, SPI6 (1), and SPI6 (2) seasons were calculated for consecutive and overlapping hydrological years (1978–1998/21 years, 1978–2008/31 years, and 1978–2018/41 years) at 28 meteorological stations. Autocorrelation, Mann–Kendall, and Sen slope trend tests were applied at a 5% significance level for each season (SPI12, SPI6 (1), and SPI6 (2)) and different time scales (21, 31, and 41 years). For each season and period, maps of the SPI drought class, average formation of drought class, Mann–Kendall (MK) trend, and Sen's slope (SS) trend test statistics for the Mediterranean region were obtained, and the spatial distribution rate of trends was determined by drawing hypsometric curves. Changes in drought occurrence at different time scales were thoroughly evaluated with the changing length of data recording. Consequently, it was determined that the mild wet (MIW) and mild drought (MID) classes dominate the study area in the Mediterranean region. Significant and nonstationary changes detected in extreme wet and drought occurrences (extreme wet, EW; severe wet, SW; extreme drought, ED; severe drought, SD) were found to pose a risk in the study area. It was observed that there were spatially and temporally insignificant decreasing drought trends in the Mediterranean basin, considering that the time scales of these trends slowed down. Despite a nonsignificant trend from the MID drought class to the MIW drought class, it is predicted that the MIW and MID classes will maintain their dominance in the Mediterranean region. The central part of the study area (central Mediterranean basin) is the region with the highest drought risk. [ABSTRACT FROM AUTHOR]

Studies associated with climate change and variability are of great importance at both the global and local scale in the global climate crisis. In this study, change-point detection and trend analysis were carried out on mean, maximum, minimum air temperatures and total precipitation based on monthly, seasonal and annual scale in Bartın province located in the western Black Sea Region of Turkey. For this aim, 4-different homogeneity tests (von Neumann test, Pettitt test, Buishand range test and standard normal homogeneity test) for changepoint detection, Modified Mann-Kendall test and Şen's innovative trend test for trend analysis, and Sen's slope test for the magnitude estimation of trends were used. According to the test results, the summer temperatures in particular show increasing trends at the 0.001 significance level. Mean maximum temperature in August, mean minimum temperature in June and August, and mean temperature in July and August are in increasing trend at the 0.001 significance level. Over a 51 year period (1965-2015) in Bartın province, the highest rate of change per decade in air temperatures is in August (0.55°C for Tmax, 0.46°C for Tmin and 0.43°C for Tmean) based on Sen's slope. However, the study showed that apart from October precipitation, there is no significant trend in monthly, seasonal and annual precipitation in Bartın. Increasing trends in mentioned climate variables are also visually very clear and strong in Şen's innovative trend method, and they comply with the statistical results. As a result, the study revealed some evidence that temperatures will increase in the future in Bartın and its environs. [ABSTRACT FROM AUTHOR]

Over the past decades, low flow has been highly impacted by climate change across Turkey, and it is important to investigate low flow trends and drivers of this change to guide water resources management. The standard normal homogeneity test (SNHT), the Pettitt test, and the Buishand range test were used for homogeneity analysis. A comprehensive assessment of trends and variability in low flows from 88 flow stations located in 26 river basins across Turkey and their attributions in a changing climate were presented. The Mann–Kendall (MK) and modified Mann–Kendall test (mMK) were utilized to detect the significance of trends, while Sen's slope method was used to identify the magnitude of trends. According to the trend test results, the low flow records of 34 stations indicated statistically decreasing trends, whereas those of four stations indicated a statistically increasing trend. We also analyzed how climate variables affect low flow variations. Correlations between climate variables (temperature and precipitation) and large-scale climate models with low flow were determined by Spearman's Rho test. North Atlantic Oscillation (NAO), Western Mediterranean Oscillation (WeMO), Southern Oscillation Index (SOI), and Pacific Decadal Oscillation (PDO) were investigated for their relation with the low flow variability. The results showed that low flow data were generally positively correlated with precipitation, and this result was particularly pronounced on the annual scale. Unlike precipitation, low flow series have a negative correlation with temperature data, and correlations are clearer during dry periods. In most areas, NAO and SO were negatively correlated with low flow patterns in Turkey, while PDO and WeMO were positively correlated with low flow series. The results indicate that low flows in most regions are more sensitive to precipitation than temperature and large-scale climate models. In addition, this research reported that the use of seasonal indices made some seasonal correlations more pronounced than their annual counterparts. These results suggest that seasonal climate indices can be potential candidates for low flow prediction. [ABSTRACT FROM AUTHOR]

In this study, trend analyses of six climatic variables (mean, minimum, and maximum temperature, relative humidity, wind speed, and precipitation) for 1966-2020 are conducted for the Southeastern Anatolia Region, which is the main focus of the integrated development project in Turkey (Turkish acronym GAP). The trends for seasonal and annual periods are determined using the Mann-Kendall (MK) test, and Sen's slope method and regression analyses are used to find the trends' slopes. Moreover, Innovative Trend Analysis (ITA) is also used to find the time series changes for low, medium, and high values. As a result of the analyses, the mean, minimum, and maximum temperatures in the GAP region show increasing trends according to both methods. Significant trends are obtained at a limited number of stations for the precipitation, relative humidity, and wind speed with the MK test, while consistent decreasing trends are found at most stations with the ITA method. [ABSTRACT FROM AUTHOR]

Trend identification procedures are used to identify systematic monotonic trendlines in a given hydro-meteorological time series recording to represent time-dependent variations as increases or decreases. Different methodologies have been proposed for such descriptions, but most of them require restrictive assumptions such as normal (Gaussian) probability distribution function (PDF), serial independence, and long sample sizes. In particular, pre-whitening and over-whitening are recommended to meet the need for serial independence, but they cannot transform a serially dependent series into a completely independent one. In this paper, a new trend methodology is proposed based on the characteristics of crossings along any given straight line within the given time series, and the sought-after trend component is the one with the maximum number of crossings. This approach does not require any restrictive assumptions. Unlike previous trend algorithms, the proposed cross-empirical trend analysis (CETA) does not give a single trend, but a series of trends at different levels within the variation range of hydro-meteorological time series records. For the sake of brevity, only three levels are considered in this article, at 10%, 50%, and 90% risk levels. The comparison of the CETA approach is presented with the classical and frequently used Mann–Kendall (MK) trend determination procedure method based on Sen's slope calculation. For very small series correlation coefficients and normal PDF function cases, CETA and the classical technique give almost the same trendline within the ± 5% error band. The application of this methodology is presented for monthly and annual discharge records of the Danube River and annual precipitation records from seven geographical regions of Turkey. [ABSTRACT FROM AUTHOR]

In this study, the trend of monthly mean and annual streamflow values of 16 streamflow gauge stations in the Tigris basin, which holds 13% water potential for Turkey, is determined. The monotonic trends are calculated using non-parametric Mann−Kendall (MK) test. To remove serial correlation from time series, a modified 'pre-whitening' method is used. The trend slopes are determined by Sen's slope method. Moreover, innovative trend analysis (ITA) method is also used to determine trends of low, medium and high streamflow values. As a result of the study, trend indicators, namely, Z values of MK tests and D values of the ITA method are compared and it has been observed that the trend directions by MK and ITA are generally similar. Nevertheless, only the negative D values calculated by ITA are mostly higher than the negative Z values calculated by MK. The ITA results of the annual mean streamflow show 80% of the stations show a strong decrease in trend for high values. Most of the significant trends found by MK are obtained in a decreasing direction, and the linear slopes are mostly determined in the range of ±2% per year. According to the spatial analysis, the significant decreasing trends are generally located in the middle region of the basin. [ABSTRACT FROM AUTHOR]

Despite the recent popularity of studying the effects of climate change on critical regions worldwide, there is a paucity of data documenting the results from trend analysis for these regions based on hydro‐climatic variables such as precipitation and temperature. The purpose of this study was to undertake a spatio‐temporal precipitation and temperature trend analysis for the Seyhan and Ceyhan River Basins located in the south of Turkey. The data for the seasonal and annual temperature variations (minimum, maximum and mean) and the total precipitation outputs obtained from the 14 stations in these basins are considered. The non‐parametric Mann–Kendall and the Mann–Kendall rank correlation tests are employed to determine the trend and its year of initiation. The linear slopes of the trends are calculated by using Sen's slope estimation technique and the spatial distributions for the slope of trends are presented. The results show that statistically significant upward trends exist for these basins based on the annual maximum temperature values, and the years of initiation of the trends are determined as mid‐1990 and mid‐2000. [ABSTRACT FROM AUTHOR]

A comprehensive evaluation of trends in annual instantaneous maximum flows (AIMF) from 153 gauge stations located in 26 river basins in Turkey is presented. Two traditional non-parametric trend tests, the Mann-Kendall (MK) and Spearman's rho (SR), are used to quantify the significance of trends, while Sen's slope method is applied to determine the magnitude of trends. The traditional tests indicate that the AIMF records of 57 stations showed statistically decreasing trends, while those of six stations showed an increasing trend. Sen's trend method, which provides more detailed assessment of the trends in different clusters (low, medium and high), was applied to the AIMF series and the results were compared with traditional tests. Sen's trend method indicated that all flow clusters at nine stations have increasing or decreasing trends, although no significant trend was detected by the MK and SR tests. [ABSTRACT FROM AUTHOR]

Trend analyses are the necessary tools for depicting possible general increase or decrease in a given time series. There are many versions of trend identification methodologies such as the Mann-Kendall trend test, Spearman's tau, Sen's slope, regression line, and Şen's innovative trend analysis. The literature has many papers about the use, cons and pros, and comparisons of these methodologies. In this paper, a completely new approach is proposed based on the crossing properties of a time series. It is suggested that the suitable trend from the centroid of the given time series should have the maximum number of crossings (total number of up-crossings or down-crossings). This approach is applicable whether the time series has dependent or independent structure and also without any dependence on the type of the probability distribution function. The validity of this method is presented through extensive Monte Carlo simulation technique and its comparison with other existing trend identification methodologies. The application of the methodology is presented for a set of annual daily extreme rainfall time series from different parts of Turkey and they have physically independent structure. [ABSTRACT FROM AUTHOR]

We investigated the spatiotemporal variability of remotely sensed gross primary productivity (GPP) over Türkiye based on MODIS, TL-LUE, GOSIF, MuSyQ, and PMLV2 GPP products. The differences in various GPP products were assessed using Kruskal–Wallis and Mann–Whitney U methods, and long-term trends were analyzed using Modified Mann–Kendall (MMK), innovative trend analysis (ITA), and empirical mode decomposition (EMD). Our results show that at least one GPP product significantly differs from the others over the seven geographic regions of Türkiye (χ2 values of 50.8, 21.9, 76.9, 42.6, 149, 34.5, and 168; p < 0.05), and trend analyses reveal a significant increase in GPP from all satellite-based products over the latter half of the study period. Throughout the year, the average number of months in which each dataset showed significant increases across all study regions are 6.7, 8.1, 5.9, 9.6, and 8.7 for MODIS, TL-LUE, GOSIF, MuSyQ, and PMLV2, respectively. The ITA and EMD methods provided additional insight into the MMK test in both visualizing and detecting trends due to their graphical techniques. Overall, the GPP products investigated here suggest 'greening' for Türkiye, consistent with the findings from global studies, but the use of different statistical approaches and satellite-based GPP estimates creates different interpretations of how these trends have emerged. Ground stations, such as eddy covariance towers, can help further improve our understanding of the carbon cycle across the diverse ecosystem of Türkiye. [ABSTRACT FROM AUTHOR]

This study comprises application of non-parametric trend analysis (Mann-Kendall test and Sen’s Slope estimator techniques) and multidimensional scaling method to water quality data sets. Water samples analyzed (for chloride, nitrate-nitrogen, sodium, sulfate and total dissolved solid parameters) semi-monthly at seven river monitoring stations in Tahtali Basin, Turkey for 6 years were evaluated. The results revealed that agricultural discharges caused spatial differences in terms of water quality in the basin. Moreover, variable concentrations generally decreased or did not change over time. This study showed that, trend detection and data grouping methods help decision makers to judge effectiveness of management programs. [ABSTRACT FROM AUTHOR]

Drought is considered to be one of the most devastating natural disasters. In recent years, determination of historical droughts has gained more importance. This can be attributed to the fact that once the trend of historical droughts is determined, it should be possible to struggle against drought more effectively. In this study, the drought analysis is performed in the Southeastern Anatolia Project (GAP) region, which is Turkey's biggest integrated project, using the monthly total precipitation data from 15 stations in nine provinces. Standardized precipitation index (SPI), being one of the most frequently used methods in the literature, is used to determine the drought indices. Temporal drought and occurrence of drought are calculated for 3, 6 and 12 month time scales. The non-parametric Mann–Kendall and Mann–Kendall Rank Correlation tests are used to determine the monotonic trends of drought indices and its year of initiation. The "Pre-whitened" method is used to remove serial correlation from time series before analysis. Linear slope of the trend is determined by Sen's Slope method, and Inverse Distance Weighting method is used for the spatial analysis. According to trends of temporal drought of the GAP region, a decreasing trend is found in 30% of the stations for 12-month SPI values with a statistical significance. Based on the results obtained from spatial analysis, there is a decreasing trend in most of the region for almost all time scales, and the slopes of trend are relatively higher in the north and south of the region. [ABSTRACT FROM AUTHOR]

Determining the change in the amount of evaporation is important for water resources management, design of water structures and preparing water action plans. In this study, trends of total monthly pan evaporation data for Gaziantep, Şanlıurfa and Mardin stations located as Southeastern Anatolia Region, which is important agricultural area of Turkey, are carried out using non-parametric Mann-Kendall (MK) and Innovative Trend Analysis (ITA) methods. The linear trend slope is determined with Sen's slope method. As a result of the study, the significant increasing trend is found with MK test in May and September at 95% confidence level and in October at 90% confidence level. The highest increase in this station according to the linear trend slope values is calculated 0.98%/year. As a result of analysis with ITA method, there is a trend occurrence in low, medium, and high values. It is concluded that ITA method can be used as an alternative method to monotonic trend analysis methods, since its ease of calculation and its ability to give results graphically. [ABSTRACT FROM AUTHOR]

ABSTRACT This study examines the spatial and temporal dynamics of wind speeds over Turkey by analysing data from 206 weather stations for a 32-year period (1975-2006). Trends in annual, seasonal, and monthly average wind speeds were determined using the Mann-Kendall trend test with the trend-free pre-whitening procedure. The strengths of trends were estimated by calculating the Sen's slope. The possible causes of wind speed changes were discussed. The analysis showed that the majority of the stations (73%) in Turkey had average wind speeds between 1.6 and 3.3 m s−1 during the 32-year period. From 1975 to 2006, 72% of stations had downward trends in annual average wind speeds. Downward trends were statistically significant at the 0.05 level for 62%. Significant upward trends were detected in only 16% of 206 stations. The rate of change in annual average wind speed data was on average −0.014 m s−1 year−1. The trends detected in monthly average wind speed data were mostly downward with an average strength between −0.007 and −0.017 m s−1 year−1. The directions and strengths of wind speed trends identified for the 1975-2006 period over Turkey are similar to the trends detected in wind speeds in many other regions over the earth. The changes in wind speeds in Turkey are most strongly related with the changes in general circulation patterns and air temperatures. The effects associated with changes in surface roughness and data quality are minor compared to other two factors. [ABSTRACT FROM AUTHOR]

Drought is a natural disaster that has potential effects on the environment, life quality, water resources and economy. It has been clustered into 4 classes which are meteorological, hydrological, agricultural and socio-economic. Hydrological drought means reductions and deficiencies in the surface and ground waters that occur as a result of the long-term lack of precipitation. In this study, using the Streamflow Drought Index (SDI) and mean monthly streamflow data from 24 stations for the time scales of 1, 3, 6, 9 and 12 months, a hydrological drought analysis for the Yeşilrmak Basin of Turkey has been investigated. Being an extreme occurrence, droughts have been identified by their length of duration and severity. Finally, in order to more accurately and thoroughly assess the trends based on the classifications of dry and wet conditions, Innovative Trend Analysis (ITA) has been enhanced by the addition of 5 vertical and 5 horizontal lines, which constitute a novel side of the study. Results shows that the distribution of percentage drought occurance, wet categories are greater than drought categories. All throughout the basin, the mild drought class dominates with the highest occurrence percentages. Furthermore, according to evaluations of drought severity and duration, the longest-lasting drought—145 months—occurs in SDI-9 from 1997 to 2009, while the most severe drought—136.13—happens in SDI-12 from 2001 to 2009. Beginning around 2000, the region has been exposed to some of the longest-lasting and worst droughts ever recorded. By IDW, it has been analyzed that different parts of the basin are affected by droughts based on time scale while SDI-9 and SDI-12 show a similar distribution in drought and wet categories. According to ITA data, there is generally a trend in most drought time scale categories, and these trends have exhibited a majority of decreasing trend characteristics. [ABSTRACT FROM AUTHOR]

Trend analysis benefits collecting and analyzing reliable data in climate change studies. In this context, long-term temperature and precipitation data analysis, two variables sensitive to climate change, is essential. This study aims to holistically and partially determine the annual trends of precipitation and temperature time series for 1970–2019 at nine selected stations in the Susurluk Basin, Turkey. The innovative trend significance test (ITST), innovative crossing trend analysis (ICTA) method, and Mann-Kendall (MK) test were used to determine holistic trends. Also, partial trends were determined using successive average methodology (SAM). For the precipitation variable, while an increasing trend was determined for the ITST, there was mostly no trend for the other methods. While a strong increasing trend was detected for the temperature according to the ITST and MK methods, no trend was observed in any station according to the ICTA method. According to the SAM results, the maximum trend durations for the peak and trough change points were 4.9 (10.3) and 5.3 (8.4) years, respectively, for precipitation (temperature). The strong temperature trends in the basin will likely continue, requiring precautions against extreme events such as drought. [ABSTRACT FROM AUTHOR]

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Precipitation is a particularly important part of the Earth's hydrological cycle and, therefore, is a necessary variable for maintaining natural balance. This study investigated past, present, and future changes in precipitation in the Marmara region, and examined the effects of global warming on this variable. The study period was from 1960 to 2020, and the climate data of 15 synoptic stations in the Marmara region were used for this purpose. To achieve the objectives of the study, linear and 6th order polynomial regression, ombrothermic and hythergraph diagrams, geostatistical models, Mann-Kendall test, Pearson correlation, standard Z-scores, and multi-layer perceptron artificial neural network models (MLP-ANN) were used to model and predict precipitation. The results of the linear regression analysis showed that of the 15 stations, 6 stations had an increasing trend, 6 stations had a trendless pattern, and 3 stations had a decreasing trend. In terms of periodic analysis, the main downward trend started in 1964 and continued until 1992, while the main periodic upward trend started in 1992 and continued until 2016. The synoptic stations in the Marmara region showed a lack of precipitation over six to seven months of the year, and the precipitation changes in the region were stronger than the temperature changes. In addition, the highest precipitation was observed on the southeast coast of the Black Sea, and the lowest precipitation was observed in the eastern parts of the region. Moreover, except for the Bilecik and Kocaeli stations, the changes in the long-term trend of precipitation at the other stations were significant. Among the 15 stations, only the Kocaeli and Sarıyer stations showed a positive correlation with global temperature during the annual period. In addition, the developed ANN model was accurate in simulating and predicting precipitation and showed an upward trend over the next seven years. [ABSTRACT FROM AUTHOR]

In this study, the historical droughts at eight meteorological observation stations in the Tigris basin of Turkey are evaluated between 1965 and 2020. The drought indices are calculated using the Standardized Precipitation Index (SPI) method for 3-, 6-, and 12-month time scales. In order to examine the change of droughts from the past to the present, three different periods designated as the first period (FP), second period (SP), and third period (TP), which correspond respectively to the time intervals of 1965–1983, 1983–2001, and 2001–2020, are taken into consideration. The trend of the drought index values is determined by innovative trend analysis (ITA). It is concluded that the mean value of the peak drought indices in the basin increased significantly from FP to TP for all time scales. The percentages of extreme and severe drought occurrences in SPI-3 and SPI-6 have increased from the past to the present. In SPI-12, although there is a significant decrease in the mean percentage of extreme drought occurrence at FP and SP, it increased considerably at TP. The trend analysis results of the SPI-3 values indicate that the number of decreasing trend stations in the basin increased from the past to the present. There is also a considerable increase in the number of stations with a decreasing trend in almost all drought classes (drought or wet) in SPI-6 and SPI-12. [ABSTRACT FROM AUTHOR]

The investigation of variability in hydrometeorological variables is crucial for water resources management and planning. In this study, trends in monthly streamflow were investigated using a novel wavelet-based Innovative Polygon Trend Analysis (W-IPTA) approach in the Konya Closed Basin, Turkey, which has semi-arid and changing climate conditions. Initially, homogeneity tests were applied to the streamflow data of thirteen discharge gauging stations, and eight of them were found homogeneous. Then, IPTA was performed, and mostly decreasing trends in mean streamflow were detected, particularly in the southern part of the basin. Increasing trends were generally observed in the standard deviation of streamflow data and the transitional period between winter and spring months in mean values in the western part of the basin. The W-IPTA indicated that decreasing trends were in short-term periods in the southern part of the basin while increasing trends were in the western part of the basin. In addition, decreasing trends were determined in the long-term period in most stations in the basin. The relationship between atmospheric teleconnections (i.e., North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and North Sea Caspian Pattern (NCP)) and streamflow data was investigated using Spearman's rank correlation and wavelet coherence analysis. A significant negative relationship between the NAO, AO, NCP, and streamflow was determined, especially in the winter months. Accordingly, it was found that the atmospheric teleconnections could be influential on the trends in the streamflow regime as well as anthropogenic and geographical factors in the basin. [ABSTRACT FROM AUTHOR]

The Euphrates–Tigris River Basin (ETRB), one of the largest river basins in the Middle East, is also among the most risky transboundary basins in the world. ETRB has a critical importance for the region both politically and economically due to its location. Evaluating the increasing regional impacts of climate change is even more important for the sustainable management of water and soil resources, especially in transboundary basins such as ETRB. Türkiye is one of the most important riparian countries of the ETRB and the Türkiye part of ETRB constitutes the headwater of the basin. In this study, the temporal variability of the annual total precipitation data for the period 1965–2020 of eighteen stations located in the Türkiye part of the ETRB was investigated. Classical Mann–Kendall (MK) test was used to statistically determine the monotonic trend of precipitation. In addition to the MK method, analyses were carried out with three innovative trend methods, which have the ability to interpret trends both statistically and graphically. These innovative trend methods are Şen innovative trend analysis (Şen-ITA), Onyutha trend test (OTT) and trend analysis with combination of Wilcoxon test and scatter diagram (CWTSD). The results obtained show that there is a decreasing trend in annual total precipitation in ETRB according to all trend methods generally used for the examined period. In addition, the results obtained from the relatively new OTT and CWTSD methods show strong consistency with the results of the other two methods. The advantages such as performing numerical and visual trend analysis with innovative OTT and CWTSD methods, identifying trends in low–medium–high value data and detecting sub-trends have shown that these methods can be used as an alternative to the widely used MK and Şen-ITA. [ABSTRACT FROM AUTHOR]

This paper investigated the trends and variability in warmest daily maximum (TXx) and warmest daily minimum (TNx) air temperatures, and heatwave characteristics in Turkey in May during 1950–2020. It also analysed the climatological and synoptic meteorological evolutions of heatwave (HW) observed in May 2020. Trend analysis revealed significant increasing trends in TXx and TNx series and heatwave characteristics in May since 1950. Since the mid‐1980s, a continuously increasing trend in TXx and TNx series, and the number, frequency, and magnitude of the heatwaves were observed that accelerated with the mid‐1990s. The most severe heatwave in Turkey since 1950 in May was observed in 2020. The record‐breaking daily maximum (daily minimum) air temperatures were noted at 32 (23) of 96 stations in May 2020, mainly over Turkey's western and southern parts. Record‐high maximum (minimum) air temperature was 43.2°C (31.1°C) reached for the first time in May since 1950. The generalized extreme value model applied to the May TXx and TNx series revealed that the daily air temperatures in May 2020 exceeded 100 years' return periods at many stations of Turkey. This heatwave was linked to a regionalized strong anticyclonic blocking anomaly circulation and other associated atmospheric anomalies in May 2020. This also resulted in the centring of an unprecedented subsiding, calm, and stable warm air mass over Turkey. Adiabatic warming and drying developed very likely under subsidence control because of relatively weak circulation conditions. Such circumstances resulted in extremely hotter conditions in May 2020 compared to the long‐term averages. [ABSTRACT FROM AUTHOR]

Drought is caused by the imbalances in the factors that make up the hydrological cycle, especially the rainfall. Droughts triggered by climate change can occur anywhere in the world. This study aims to conduct a detailed seasonal drought analysis through the monthly precipitation statistics of 126 observational points in Turkey during 1925–2016. The drought analysis was performed for four different periods: 1925–1949, 1950–1974, 1975–1999, and 2000–2016. First, the standardized precipitation index values were calculated with the Pearson Type III distribution. The 3-month period, used in seasonal drought analysis, was preferred. Information about the course of drought was obtained with the Mann–Kendall trend analysis. The severity, duration, and frequency of drought were found with the Theory of Runs model. The joint return period of drought severity and drought duration were obtained with the copula approach. The mapping was done with the inverse distance weighted method. The findings indicate that the lowest SPI value (− 2.12) was observed in spring 1972 and the highest SPI value (2.14) was observed in winter 1941. Very dry conditions were recorded with a frequency of 16% in the spring season of the 1925–1949 period; the most normal arid conditions were documented in the autumn season of 1950–1974 with a frequency of 52%. Extreme drought conditions were reported in the spring season in 1992. While there was an insignificant increase in drought in spring, summer, and winter, a significant increase was observed in autumn especially interior parts of Turkey. Theory of Runs results indicate that the highest intensity, with a value over 2, was observed in the southeast of Turkey during the winter and spring seasons during the 1925–2016 period. The Frank copula function was found to be the most suitable function in calculations of the drought severity and duration calculation for Turkey. The return periods of weak, moderate, and severe droughts were between 127.53 and 78.96, 68.85 and 59.60, 60.28 and 57.65 months, respectively. It was determined that the drought severity increased in the inner regions during the 20- and 100-year drought return periods with the values varying between 5 and 16, 7, and 32, respectively. [ABSTRACT FROM AUTHOR]

This study characterises the spatial and temporal behaviours of maximum precipitation over the Black Sea Region in northern Turkey. Maximum precipitation data of 14 standard durations changing from 5 min to 24 h were used from 21 meteorological stations in the region with record lengths ranging from 25 to 71 years. In line with the objective of the study, tests for the detection of outliers, homogeneity, and trend were applied in order to reveal the structural characteristics of the data set. Tests detected no outlier, and the homogeneity analysis found only three stations fully homogeneous, all others being inhomogeneous. Change points identified in the data set by the homogeneity tests were linked to the local characteristics of meteorological stations. Trend analysis revealed that slightly more than half of the meteorological stations are exposed to a positive trend in the maximum precipitation of one standard duration at a minimum. The main conclusion is that maximum precipitation is subject to change over the Black Sea Region in Turkey. [ABSTRACT FROM AUTHOR]

The aim of this study is to conduct a drought analysis at Kars station in the northeast of Turkey using six different meteorological parameters by utilizing The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method based on the entropy weight method. As of the input parameters of the study, the mean monthly rainfall, mean monthly maximum and minimum temperature, mean monthly relative humidity, mean monthly wind speed, mean monthly sunshine duration, obtained by the Kars meteorology station for 1990 and 2018 period are used. In the second section of the study, Mann–Kendall trend analysis was applied to TOPSIS results. The findings of this study indicated that the drought tends to increase in January, May and October. In the final section of the study, multivariate regression analysis, which accepts six different parameters as independent variables and TOPSIS drought index results as dependent variables, was performed. According to the findings of this study, there were no cases of extreme wet, severe wet, medium wet, severe drought and extreme drought at the Kars station. The driest months are May and June. The wettest months are March and November. [ABSTRACT FROM AUTHOR]

The issue of detection of hydrometeorological trends remains relevant because of the importance of climate change in design, operation, and management studies related to water resources. This study examines the effects of changes in climate and land use on monthly flows (1962–2018) in the Eastern Black Sea basin, Turkey, using innovative trend analysis methods. In this context, innovative polygon trend analysis (IPTA) and innovative trend significance test (ITST) were used to detect the trends and compared with Mann-Kendall test. Only stations with homogeneous data that did not experience non-climatic changes are used in the analysis. IPTA and ITST approaches are much more sensitive than Mann-Kendall in detecting trends. Although the innovative methods are mostly compatible with each other (90%), IPTA presents additional information about trend transitions between successive parts of time series. Results indicate significant decreasing trends in summer months, likely due to diminishing precipitation and effective evaporation. [ABSTRACT FROM AUTHOR]

Climate change is an event that has significant effects as direct or indirect on ecosystem and living things. In order to be prepared for the effect of climate change, it is necessary to anticipate these changes and take measures for this change. Therefore, many studies have been carried out on changes in climate parameters in recent years. The most common method used in these studies is trend methods. Innovative Polygon Trend Analysis (IPTA) and Trend Polygon Star Concept are trend analysis methods. IPTA Method divides data series into two as first and second data set and analyzes these two data sets by comparing them with each other. Trend Polygon Star Concept analyzes distance between two months in data set in graph, which is result of IPTA, and shows analysis result by dividing it into four regions. Therefore, in this study, monthly average temperature data are analyzed by using this two-polygon method. This data set is for 22 years (1996–2017). Polygon graphics were created as a result of study. Besides, trend slopes and lengths of temperature data with IPTA Method were calculated. The values of graphs created with Trend Polygon Star Concept Method on x- and y-axis were given in a table. When the results of both analysis methods were examined for a station, the following results were observed. For example, a regular polygon was not seen in arithmetic mean and standard deviation graphs of IPTA Method of Bandirma Station. Besides, when general evaluation of arithmetic mean analysis results was examined an increasing trend in most months. When arithmetic average graph created by Trend Polygon Star Concept Method of Bandirma Station was examined, transition between two months was seen first and third region. When standard deviation graph was examined, transitions between two months were seen in all four regions. [ABSTRACT FROM AUTHOR]

The analysis of long-term rainfall data in a changing climate is important because it has many sectoral applications such as agriculture, infrastructure, and water resources management. Statistical analyses of the annual maximum rainfall data were performed using the Mann–Kendall (MK) trend test to evaluate the annual maximum trend characteristics of the rainfall time series, the innovative trend analysis (ITA) method to detect categorial trends, and the ITA indicator to digitize the ITA results. Storm durations of 5, 10, 15, 30 min and 1, 3, 6, 24 h annual maximum rainfall series at 13 central stations in Central Anatolia, Turkey were used. According to the MK test results, there were no significant upward or downward monotonic trend at four stations, whereas the remaining nine stations showed a significant upward or downward monotonic trend. Significant negative and positive trends were identified for the sub-hourly and hourly rainfall, whereas significant positive trends were detected for hourly storm durations. Significant trend results were mostly consistent with the general ITA results. The sub-hourly storm duration data were more consistent in terms of significant trends. Conversely, when evaluated according to low, medium, and high data values in the rainfall series (categories), the high data values showed different trends. Although no trend was detected with the MK test, the ITA results showed an upward or downward trend for 25 rainfall series. 29 of 30 significant MK test results were consistent with the ITA indicator results, compared with 24 of 30 results of the visually inspected ITA results. [ABSTRACT FROM AUTHOR]

In this study, annual and seasonal precipitation trend analysis was performed in the Euphrates-Tigris basin, Turkey, using innovative trend analysis (ITA) and discrete wavelet transformation. In this context, it was seen that there is a downward trend in winter, spring and annual precipitation, whereas precipitation has an increasing tendency in summer and autumn seasons, in the greater part of the basin. When annual and seasonal data were decomposed into wavelet components, the most significant trends were observed for high-periodic wavelet components, such as D3 (8-year), D4 (16-year) and D5 (32-year), where these components represent the periods of the precipitation data. Then, the relationship between North Atlantic Oscillation (NAO) and trend in precipitation was investigated. In this regard, it was found that there could be a significant relationship between the NAO and precipitation trends of the Euphrates-Tigris basin, especially in winter, based on the wavelet ITA. [ABSTRACT FROM AUTHOR]

In this study spatial and temporal variations of climatic growing season parameters in western Anatolia, Turkey, during 1966-2015 are analysed. The beginning of the growing season (end of the growing season) for all threshold values of 5, 7 and 10°C is delayed (advances) from the southwest to the northeast over the study area. The growing season length (GSL) increases from northeast to southwest. The growing season start (GSS), growing season end (GSE) and GSL are strongly correlated with elevation, low-elevation stations having earlier GSS, later GSE and longer GSL than stations at higher elevations. The regional average GSS shifted 7.3, 10.0 and 10.5 days earlier, while the regional average GSE moved 4.8, 6.1 and 6.2 days later, increasing the GSL by 12.0, 16.6 and 15.9 days for 5, 7 and 10°C, respectively. A comparison of mean values between subperiods documented significant changes at more than 50% of stations for GSS and GSL from the subperiod 1977-1997 to the subperiod 1998-2015 and almost no significant change between 1966-1976 and 1977-1997 for all thresholds. Correlation analysis showed that the East Atlantic Pattern was the main driver for GSS and the North Sea--Caspian Pattern for GSE, followed by the East Atlantic/Western Russia Pattern and the North Atlantic Oscillation, respectively. Monthly and annual precipitation totals and precipitation distribution within a year have not changed significantly, suggesting that air temperature has become more influential on GSS and GSE. [ABSTRACT FROM AUTHOR]

The aim of the study was to evaluate the sediment prediction performance of Revised Universal Equation (RUSLE) and Musgrave Equation at the Ekinli pond catchment, North central part of Turkey. Ekinli pond was built in 1977 for irrigation purposes. The accumulation of sediment in the ponds negatively affects their functions. There are many dams located within the study area whose operations have been adversely affected by excessive reservoir sedimentation. Accurate estimation of sediment deposition is important in the design of a pond. The calculated amount of sediment volume deposited in the Ekinli reservoir was 21600.75 m³ and the average sediment yield was 514.3 m³ y-1 between 1977 and 2018. In the Ekinli basin, the availability of bathymetry measurements between 1981 and 2006, provided the appropriate conditions to validate the results of the predicted sediment yield since the deposited sediment volume could be quantified as 552.3 m³ y-1. The measured and estimated sediment amounts for the Ekinli reservoir have shown an excellent accordance. In the 42-year time period, 6.74% of the water storage capacity of the pond has been lost. From 1977 to 2000, the entire basin was grassland and 38% of the basin area has been afforested. The landuse change reduced a little the amount of sediment in the reservoir. The Mann–Kendal and Theil–Sen Slope estimator statistics indicated a decreasing trend of sediment amount. [ABSTRACT FROM AUTHOR]

This study was performed by the reevaluation of historical Universal Soil Loss Equation using field experiment data that was obtained between 1978 and 1995 in Tokat, Turkey. In the study area, the annual average rainfall was 452 mm and about 50% of erosive rainfall events were less than 10 mm. The duration of average erosive rainfall event was 6 h and the average event intensity was 3.83 mm h-1. The average erosive rainfall time in daylight (06:00-18:00), night (18:00-06:00) and mix rainfall conditions were 223.1 and 191.6, 450.2 min, respectively. The maximum rainfall amount, event intensity, storm erosivity, the maximum intensity of 10 min (IM10), the maximum intensity of 15 min (IM15), the maximum intensity of 30 min (IM30) were mostly occurred in daylight erosive rainfalls. But the maximum soil loss and runoff produced by night erosive rainfall. This situation was attributed to the short-term effect on soil erodibility of day and night temperature differences in spring which is rainfall erosivity is high for the region. Higher correlation is observed between soil loss and IM10 compared to IM30. USLE R-factor showed a good correlation with Modified Fournier Index (MFI) for the region. The Mann–Kendal and Theil–Sen Slope estimator statistics to detect the direction and magnitude of an available monotonic trend in some erosivity parameters as well as soil loss and runoff. Trend analysis showed monotonic decreasing of all rainfall physical properties, soil loss and runoff. [ABSTRACT FROM AUTHOR]

This paper addressed the spatial and temporal variations of precipitation concentration across western Turkey, by analyzing daily and monthly precipitation time series recorded at 28 stations over the period 1966-2011. Four indices: daily precipitation concentration index (DPCI), monthly precipitation concentration index (MPCI), precipitation concentration degree (PCD) and precipitation concentration period (PCP) were used. The results showed higher values of DPCI in northwestern and southern parts and lower values in western-central, central, eastern and northeastern parts, and the southern part was the most critical part of the study area, with the highest values of DPCI, MPCI, PCD and annual total precipitation, but the lowest number of rainy days. MPCI and PCD values showed a seasonal precipitation regime over the whole study area and exhibited a pattern decreasing from southwest to northeast, which implies a more uniform distribution of monthly rainfall in a year toward the northeast. PCP values showed that annual precipitation mainly falls in December and January. Trend analysis demonstrated mostly non-significant decreasing trends for all indices, implying a very slight tendency toward a more regular precipitation distribution in a year and a slightly earlier occurrence of precipitation over western Turkey. [ABSTRACT FROM AUTHOR]

ABSTRACT Soil temperature change is reported to be an important indicator of climate change, as soil temperature integrates all processes occurring at and above the soil surface. Analysis of long-term trends in soil temperatures and their relationship to climatic variables could provide valuable information on climate change. In this study, soil temperature trends were analysed on seasonal and annual scales at depths of 5, 10, 20, 50 and 100 cm over the period from the 1970s to 2006 at eight sites in the Büyük Menderes Basin in Western Turkey. Also, air temperature, rainfall and sunshine duration records were analysed for trends, and for their correlations with soil temperatures. The results showed a general increase in soil temperatures at all depths and in all seasons. The most significant warmings were observed in summer, especially in the upper layers (5, 10 and 20 cm). The trend magnitudes ranged from −0.91 to 2.05 °C decade−1, depending on site, season and depth. It was observed that air temperature had a clear and dominant influence on soil temperature change. Soil temperatures were also affected by sunshine duration and rainfall. These findings are expected to contribute to our understanding of the linkage between soil temperature change and global warming. [ABSTRACT FROM AUTHOR]

ABSTRACT New investigation techniques for detecting hydro-meteorological data trends are required due to significant changes in precipitation and streamflow affecting the planning and operation of water resources. In this study, the trends analysis is carried out for the observation of climatic and hydrologic parameters such as temperature, humidity, precipitation and streamflow in the Euphrates Basin located in the Southeastern Anatolia Project (referred to as GAP from the Turkish acronym for Güneydoǧu Anadolu Projesi) region, which is the most important integrated water resources project in Turkey. The relationships between different meteorological and hydrological parameters in the basin are evaluated using the overlay mapping technique, popular in various engineering disciplines. The significant trends are indicated on the thematic maps and the visible changes are observed in different parts of the basin. Decreasing trends are detected in minimum streamflow, while the increasing trends in the annual mean and maximum temperature and in the annual mean and maximum humidity parameters are observed for many stations. The study concludes that the overlay mapping technique can be used effectively to observe the climatic changes and trends in hydrometeorological variables. The results are expected to help water resources managers and policy makers in decision-making for better planning in water resources planning and management. [ABSTRACT FROM AUTHOR]

Accurate knowledge of solar irradiation reaching the earth's surface is one of the most important pieces of information to use in global warming studies. In this respect, trend analysis of solar irradiation data for the long term is an essential evaluation method of climate change. Sunshine duration data have been recorded for many years, directly correlated to solar irradiation. Therefore, trend analysis of sunshine duration data is also an important research topic of climate change. Global research from different regions of the earth showed diming (1950s to about 1980s) and brightening (about 1980s to recent years) periods in solar irradiation. The present work aims to obtain the trends of the measured sunshine duration over Turkey. Seasonal and yearly bright sunshine hours of 36 selected stations are used and quite similar trends are seen. A decreasing trend (between 1970 to about 1990) is clearly identified for most of the stations. Nevertheless, the increasing period after 1990 is not so clear; however, we observed either zero trend variation or a reduction in the rate of decrease of sunshine duration for most of the locations. The decreasing period might be attributed to human-induced air pollution. [ABSTRACT FROM AUTHOR]

Detection of changes over the long term for a series of hydrological variables is an important and critical issue, which is subject to increasing interest. In this study, trend analysis of the streamflow of the Euphrates basin, which is the biggest basin in Turkey, is carried out. The nonparametric trend tests (Mann-Kendall and Spearman's rho) are applied to annual average, minimum and maximum streamflow data of 22 selected stations in the Euphrates basin. All the streamflow records date back over at least 24 years, with lengths in the range 24-44 years. The Mann-Kendal rank correlation test is used to determine the year in which trends begin. The linear slopes of trends are calculated by using Sen's estimator of slope technique. Based on the test's procedures, with respect to annual minimum streamflow, significant decreasing trends are detected for six stations and an upward trend is found for only one station. While no trend appears relating to annual maximum streamflow for any station, a decreasing trend is found with respect to annual mean streamflow for one station. The results are expected to assist water resources managers and policy makers in making better planning decisions in the Euphrates basin. [ABSTRACT FROM AUTHOR]