جستجوی مقالات مرتبط با کلیدواژه « تخمین گر شیب سن » در نشریات گروه « جغرافیا »

This study investigated the trend of hydroclimate parameters of the Miankaleh wetland using the Mann-Kendall test and Sen slope estimator. Temperature, precipitation, and evaporation parameters were used from the synoptic stations . Also, the discharge data were used from the hydrometric stations of Khalil Mahalleh, Tazeh Abad, Baghoo, and Vatana stations. The results of the Mann-Kendall test showed that the temperature in the Dashte-Naz station in spring and summer seasons has a significant increasing trend with 95% confidence and a significant decreasing trend in winter. Also, there is an increasing trend in Hashem Abad station, with a 95% confidence level in the spring and autumn seasons. Precipitation in Dashte-Naz station with a 95% confidence level has a decreasing and increasing trend, respectively. The most frequent trend changes in Dubai are related to Vatana station, which has a decreasing trend on an annual scale. Evaporation in Dashte-Naz station has a decreasing trend in the autumn and winter seasons and has an increasing trend in spring. Also, in Hashem Abad station, the evaporation rate in autumn has a decreasing trend. The Sen slope estimator method results showed that precipitation in Dashte-Naz station in December was -2.983, and on the annual scale, it is related to Hashem Abad station with -6.283. The highest monthly positive trend line slope of all parameters is related to August precipitation in Dashte- Naz station with a value of 3.20, and the highest annual scale is related to evaporation in Hashem Abad station with a value of 2.157.

Changes in hydrological-climatic series can occur in different ways. Change can occur suddenly or gradually (trend) or in more complex forms. In general, trend analysis is performed to obtain information and study whether a trend or a pattern can be extracted from this information. Information about precipitation trends is important, because precipitation trends are related to water-related problems in the region, environmental and water management goals. This information will be the most valuable when studying climate change and its effects on water resources management. Determining the precipitation trend has been one of the most important activities of hydrologists and meteorologists in advancing climate change studies. In addition, the study of climate change requires information on the trend of various indicators (hydrological and climatic) because climate change is a continuous change. Almost all water and meteorological parameters are affected by climate change phenomenon. Precipitation is one of these variables that strongly affects the environment and the hydrological cycle. The temporal changes of precipitation are important both from scientific and practical point of views, since they strongly affect water resources. Therefore, studying the process of these changes is very important for short-term and long-term management planning. The importance of this study increases when we face time and place limitations of rainfall in an arid and semi-arid region like Iran and especially in Fars province. Therefore, in the present study, the 30-year trend of precipitation was investigated in 27 rain, synoptic and evapotranspiration stations in Fars province. The study of rainfall changes was done at annual and seasonal and at both stational and regional scales. At the first step, monthly precipitation data was gathered from meteorological organization and water resources management company. Then monthly data was converted to seasonal and annual data sets. Mann-Kendall methods, age slope estimator and linear regression analysis were used to conduct at point analysis. In order to study the rainfall trends at regional scale, first, the study area was clustered based on mean seasonal and annual precipitation using the K-mean clustering method. It is worth mentioning that for each season and annual, separate homogenous regions were formed. Then regional Mann-Kendall method was utilized to investigate the trends in each homogenous region. On an annual scale, a decreasing trend of precipitation was observed at all stations. But Arsanjan, Berghan, Tangab Firozabad and Farashband stations are the only points whose rainfall trends are significant at the 95% confidence level. On a seasonal scale, a decreasing trend of precipitation was observed in almost most seasons and most of the stations. Except for the summer season, when we see a very slight increase in the majority of the stations. In spring and summer, respectively, 48% and 67% of the stations witness a decrease in precipitation, but these trends are not significant. In the autumn season, 74% of the stations experienced a negative trend of precipitation, and among these stations, Arsanjan, Berghan, Shiraz, Farashband, Kazeroon, Madersaliman and Zarghan witnessed a significant decreasing trend at the 95% confidence level. At the regional level, on annual and seasonal scales, the entire province has seen a decrease in rainfall, especially in winter and annual rainfall. This decrease in rainfall in the northwest of the province is a little weaker than other parts of the province. In the spring season, decreasing changes were observed, but these changes are not significant. In the summer season, a significant increase was seen in rainfall in the southern part of the province. This may be due to the increased activity of the Indian Monsoon. In the autumn season, a decreasing trend in the whole province was experienced, which is not significant. Similarly, the winter season also a decrease in precipitation was observed, with the difference that this trend is significant at the 95% confidence level. In general, all point and regional analyzes show a decrease in precipitation, especially in the annual and winter scales. On the other hand, there are signs of an increase in rainfall in the summer season. Considering that most of the province's annual rainfall occurs in the winter season, the decrease in rainfall in this season can have irreparable negative effects, which of course it has done so far. Therefore, it is expected that more attention must be paid to the planning of the water management and agriculture. In addition, due to the signs of increased rainfall in the spring and summer seasons, there should be sufficient attention to the problem of flooding in these seasons and the resulted damages, and in general, the comprehensive management of water resources in these changing conditions should be seriously considered so that the minimum losses and maximum benefits could be obtained.

In this research, the daily data of geopotential height of 500 hectopascals (hPa) with a spatial resolution of 1 degree from the ECMWF database for Southwest Asia and rainfall station data from the National Meteorological Organization (1979 to 2018) have been exerted. The technique used the principal component analysis and cluster analysis. With these analyses, nine circulation patterns were identified. The changes in the patterns were tested at the 95% significance level by the non-parametric Mann-Kendall test, and Sen's slope estimator was exerted to estimate the number of changes. The significance test of the trend for the winter patterns in Iran's rainy season revealed the significant trend of increasing the height of the geopotential, which has led to a decrease in the pressure gradient and a decrease in instability, and finally, a weakening of the winter precipitation patterns. Significant positive trends of geopotential height showed the continuation of these conditions for summer patterns (increasing stability, decreasing rotation, and decreasing precipitation). Of the nine known patterns, only one seasonal pattern showed a significant negative trend in the country. This pattern, with a slight increase in rainfall, indicates the formation of unstable conditions, which can lead to moderate-season rains if moisture is available. The findings showed that a rainy winter pattern had been eliminated in the last two decades, and a summer pattern had appeared instead.

Knowledge of groundwater quality and quantity changes is needed for an appropriate management and optimum utilization of groundwater resources. Many different statistical methods are available for detecting and estimating trends present in water quality parameters. These methods range from the simple correlation and regression analyses to time-series analyses and nonparametric approaches. Analysis of the time series is the most common technique used to detect changes in climate and hydrologic phenomena. Trend analysis can be defined as the use of an experimental approach to determine and explain the changes in a system over a period of time in statistical terms. In nonparametric methods, unlike parametric approaches, fewer assumptions about the data frequency distribution (e.g. normality of the data distribution) need to be made. Besides, the knowledge about spatial distribution pattern of groundwater quality is required for a sustainable and appropriate groundwater management. The nonparametric tests of Mann-Kendall (MK) and Spearman’s rho (SR) are commonly used to evaluate the trend of changes in climate and hydrology data. The aim of this study is to use Mann-Kendall and Spearman methods for investigating the changes in groundwater quality in Khash region during 2004-2013, according to the data of 17 stations. The slope of the trend line for all variables is calculated using Sen's estimator. Moreover, ordinary kriging is used to predict the spatial distribution pattern of groundwater quality parameters. Matherials and Methods: The study area is Khash region located in Sistan and Baluchestan Province. The study area is located between 61-00 to 61-45 latitudes and 27-45 to 28-40 longitudes. Groundwater quality parameters studied include acidity (pH), electrical conductivity (EC), sodium (Na+), sodium percentage (Na%), sodium adsorption ratio (SAR), sulfate (SO42-), the bicarbonate ion (HCO3-), chlorine (Cl-) , magnesium (Mg2+), calcium (Ca2+), potassium (K+), total cations, total anions, total hardness (TH) and dissolved solids (TDS). The data were collected from 17 stations during 1383-1392. The Spearman's rho, Mann-Kendall and Sen's estimator tests were used for detecting trend in quality parameters of groundwater. A brief representation of the methods used is provided as following: In this study Mann-Kendall (MK) and Spearman’s rho (SR) tests are used to analysis the trend of changes in groundwater quality data over Khash plain. The slopes of the trend lines can be estimated by using a simple non- parametric procedure called the sen’s slope estimator. To better investigate the groundwater quality changes over 2004 to 2013 across the whole area, the spatial distribution patterns of quality parameters are mapped using ordinary kriging (OK) interpolation method. OK estimator estimates the unknown values of a groundwater quality parameter through a linear weighted moving average of surrounding data values. Discussion of Results: In this study, the annual changes in groundwater quality in Khash region during the period 2004-2013 with the Mann-Kendall and Spearman nonparametric methods were studied. Sen's estimator slope was used to estimate the slope of the trend line for qualitative variables. The results showed that the majority of water quality variables have positive trend at most stations. The strongest positive trend (Mann-Kendall ’Z=3.93 and Spearman ’Z=3) was seen for EC at station number 4. Based on the results of the Mann-Kendall test, stations numbers 4, 10, 16 and 17 had the most significant positive collections. Also EC, TDS, K+ and Cl- had the most significant collections are among other variables. The results of Spearman method showed that the stations 4, 10, 15 and 16 have more significant positive trends. Ca2+ and SO42- had more negative trends at most stations. The most significant positive trends have seen for EC and TDS, followed by K+, Na%, Cl-, TH and HCO3- in the majority of the stations. According to this method, SO42- tends to decrease in the most of the stations. Sen's estimator results showed that the stations 10, 8, 1, 14, 15 and 16 had more positive slopes. According to these results, EC, TDS, Na%, Na+, SAR, HCO3-, Cl-, pH and total cations have increased in most stations. According to the results of all three methods (Mann-Kendall, Spearman and Sen's estimator), stations 10 and 16 are critical situation. The results of the Mann-Kendall and Spearman showed that EC and TDS have increased at most stations. Also, the slope of these two variables is positive at most stations. The results of all three methods showed that SO42- tends to decrease in the most of stations. According to the maps generated using ordinary kriging, the amounts of %Na, SAR, pH and HCO3- increased from 2005 to 2013. To investigate the factors affecting the quality of groundwater in the area, trend analysis of rainfall was also performed. Mann-Kendall and Sen's estimator test results showed that both stations had negative trends of annual rainfall. The results showed a decrease in rainfall, which reduces the volume of water entering the aquifer. Excessive groundwater withdrawals, population growth and development of industrial life are among the factors decrease the water quality in the study area. Conclusions: The results of this study showed that the Mann-Kendall and Spearman methods have similar performance in detecting stations with degrading water quality. According to the results, EC and TDS tend to increase and SO42- tends to decrease in most stations. Groundwater quality in stations No. 10 and 16 showed the most meaningful positive trends among others. Middle slope of the trend line was positive for 70% of the plotted curves. In general, the results showed a positive trend of groundwater quality parameters in most stations meaning that groundwater quality tends to decrease in this region over time. Low amounts of rainfall, excessive groundwater withdrawal, population growth and development of industrial life are the main factors threaten groundwater quality in the area. To prevent further groundwater quality degradation and protect the water resources for future generation, appropriate management strategies should be considered.

Thunderstorms are climatical phenomena, which sometimes can cause irreparable damage to the ecology. In this study to identify any trends in the frequency of days with thunderstorms in Iran, long-term statistics of 33 synoptic stations, from the beginning until 2005 was used. At first by applying nonparametric Man-Kendall and Sen’s Estimator methods on four seasonal time series, and one annual time series for each station, their significance is assessed. Also, for recognizing the starting years of this trend, Man-Kendall step by step test plot was employed. Results are showing that the maximum spatial frequency of days with thunderstorms across Iran is a function of time. Evaluation processes using both tests indicate that all significant trends in all series except the annual series of Bam stations are increasing. So due to these two test similarity, the trend of thunderstorms in all five time series could be considered increasing which maximum and minimum of trends belong to annual and wintery time series respectively; So the trends annual time series of 58% of the stations were significant. Also the step by test revealed that in annual time series most of the significant trends have been started from decades of 70 and 80.