جستجوی مقالات مرتبط با کلیدواژه « من-کندال » در نشریات گروه « محیط زیست »

Precipitation is one of the elements of climate that has great variability. These changes occur both in terms of time and space in many regions of Iran. Knowing the characteristics of this atmospheric element is very important for many construction plans, plans and agricultural activities. Any statistically significant change in this element can impose inevitable negative effects on natural resources, especially recoverable water reserves. Knowing the change process of climatic parameters is one of the things that has been the focus of atmospheric and hydrological science researchers in recent years. Most of the studies have been focused on investigating and analyzing the behavior of precipitation, and Mann-Kendall statistical methods have been widely used as the most common non-parametric method for analyzing the trend of precipitation time series. Since the trend finding in terms of the frequency of convective Precipitation has been less noticed by researchers, the purpose of the present study is to investigate the trend of the frequency of convective rainfall in the first half of the year in synoptic stations located in the northwest of Iran. In this research, the study area for the statistical analysis of convective precipitation includes Ardabil, East Azerbaijan, and West Azarbaijan provinces.

To carry out this research, the daily Precipitation data in the first half of the year (April, May, Jun, Jul, Aug, Sep), in synoptic stations located in the northwest of Iran (including Ardabil, Ahar, Urmia, Bonab, Bostan Abad, Tabriz, Pars Abad), Khoy, Sarab, Sardasht, Khalkhal, Marand, Mianeh, Mako, Mahabad, Meshkin Shahr and Maragheh were used during a 17-year period (2000-2016) and daily Precipitation of at least 5 mm was considered as convective Precipitation. Then, the annual frequency of convective precipitation of each station was counted and trending methods based on Mann-Kendall statistical method and Sen’s slope estimator nonparametric method were used to analyze its trend. The Mann-Kendall test does not require a normal frequency distribution or the linearity of the behavior of the data, and it works very strongly compared to the data that deviates from the linear behavior and is used to evaluate the trend. In this test, the null hypothesis (H0) and the opposite hypothesis (H1) are respectively equivalent to no trend and the presence of a trend in the time series of observational data. In Sen's method, the time series is divided into two groups, and the numbers of each time series are arranged in ascending order. Then these two series are plotted against each other on the coordinate axis. It is better to draw the first time series on the horizontal axis and the second series on the vertical axis. In the next step, the 1:1 line is drawn, if the points are above the line, there is an increasing trend, below the line, there is a decreasing trend, and on the line, the data will be without trend.

The changes of precipitation in Tabriz station have been decreasing since 2006 and because these two components outside the critical range (±1.96) have intersected each other in 2013, 2014, and 2015, this trend is not significant. This situation happened at Maragheh station in 2013 and 2014, and since 2015, a decreasing trend in rainy days has been seen, at Midane station, since 2015, there has been a change of direction in the abundance trend from a non-significant increase to 2015. In other stations of East Azarbaijan province, during the studied period, no specific mutation and trend in the frequency of convective precipitation can be seen, and in fact, these stations have no trend. In Sardasht station, the time of the beginning of decreasing and then increasing changes in the frequency of convective precipitation in the years 2000, 2002, and 2016, the two components Ui and Ui' are outside the critical range, which is not significant. A sudden change in the direction of this variable occurred in Mako station in 2001, which is incrementally insignificant. At Urmia station, several sudden changes in the frequency of convective precipitation can be seen during the studied period, which started from 2001 and continued until 2008. The trend of convective precipitation in 2003 was decreasing and after 2007 it was increasing insignificantly. In Mahabad station, the intersection of Ui and Ui components in 2001 reveals an increasing trend in the frequency of convective precipitation. In addition, in 2012, these lines intersected outside the critical range of ±1.96, which shows the increasing trend of the frequency of convective precipitation of a non-significant type. In Khoy station, between the years 2000, 2003, 2006, and 2007, a significant and sudden change began, which is insignificant. For the entire province of West Azerbaijan, a sharp and sudden change in the direction of an insignificant increase can be seen from 2003 to 2013. This sudden change has been revealed in the form of a decrease in 2013, which is not significant. In Parsabad and Meshkinshahr stations, the two components Ui and Ui' have not met each other inside and outside the critical range, and in the years 2008 and 2009, a significant decreasing trend started, which is insignificant, but in Ardabil station, these two components are within the range. In the years 2006 and 2010, they met each other, which indicates the beginning of a change of direction and a decreasing trend, albeit insignificant, in the frequency of convective precipitation at this station. This situation occurred in Khalkhal station in 2001 and 2008, which was accompanied by an increase in 2001 and an insignificant decrease in 2008. In general, the results of the analysis of the frequency of precipitation with the Mann-Kendall test showed that the variable trend, both increasing and decreasing, in the stations is not significant due to the location of the intersection point of Ui and Ui' outside the critical range (±1.96). In this way, the frequency of precipitation in the stations of East Azarbaijan province including Tabriz, Maragheh, Bonab, and Sarab shows a non-significant decreasing trend, and in Marand, Ahar, Bostan Abad, and the middle of a non-significant increasing trend, in the stations of West Azarbaijan province (including Urmia, Mako, Mahabad), Sardasht and Khoy) has had a non-significant increasing trend in the stations of Ardabil province (Parsabad, Ardabil, Meshkin Shahr, and Khalkhal). The results of trend analysis using the age slope estimator method show an increasing trend in Mako, Urmia, and Meshkinshahr stations. Also, the frequency of rainfall in Bostan Abad, Mahabad, Ardabil, and Parsabad stations has no trend and in other stations, it shows a decreasing trend without significance.

Horizontal visibility is one of the most important optical characteristics of the atmosphere. Predicting horizontal visibility is of great importance in various aspects such as air pollution, air traffic, flight safety, road traffic, and maritime travel safety. The aim of the present study is to analyze the spatiotemporal variation of horizontal visibility in the southern coasts of the Caspian Sea. For this purpose, hourly data of horizontal visibility, present weather phenomenon, and relative humidity were used for a 70-year statistical period (1951-2020) in the study area. In this study, the extinction coefficient was calculated using the Koshmider formula. Finally, using the non-parametric Mann-Kendall test, the trend analysis of the frequency reduction of horizontal visibility phenomenon was conducted in the region. The results showed that among the studied stations, Babolsar, Ramsar, and Astara stations experienced an increasing trend, Nowshahr station experienced a decreasing trend, and Gonbad-e Kavus and Maraveh Tappeh stations had no trend in the extinction coefficient. Based on the Mann-Kendall output among the seasons, significant decreasing (increasing) trends were observed in the autumn and winter seasons, and no trend was observed in other time scales. The results of the analysis of the impact of weather parameters showed that among the factors affecting horizontal visibility, precipitation (39.75%) and dust (0.83%) had the highest and lowest percentage of impact, respectively, compared to other effective factors in the region. In general, it can be said that due to the forested nature and suitable vegetation cover in the region, the possibility of the occurrence of local dust storms is very low.

Land use/land cover (LULC) change, strongly affects surface water characteristics, especially in urban watersheds. The aim of this study was to determine LULC in the Samian Watershed and assessing its relationship with water quality parameters. In this study, LULC maps was obtained by ENVI software in four periods (1992 to 2016). Then, 9 water quality parameters at five river gauge stations were selected for further analysis. The Mann-Kendall test was performed to examine the trends in water quality parameters and Pearson test was used to assess the correlation between quality parameters and land uses. According to the results, rangeland decreased by 9.75%, irrigated agriculture increased by 8.45%, residential increased by 1.42% and rainfed agriculture increased by 3.29% compared to the first period. Average of TDS and EC in the study periods in Samian and Gilandeh stations, has been increased. The correlation analysis using Pearson test between quality data and LULC also shows that the EC, Ca, Cl, SO4, Mg and Na pameters of had a significant relationship with increasing residential, irrigated and rainfed land uses.

The study of snow cover changes, as one of the sources of water supply is very important. The purpose of this study is to investigate the trend of snow cover changes in Tehran province using MODIS sensor images of Terra satellite and Aqua satellite (since 2003) until the end of 2018 and compare the performance of MODIS sensor in these two satellites. The trend of snow cover satellite images changes was determined by ETM analyzer of TerrSET software, their significance was determined by non-parametric methods of Mann-Kendall significance test. Then, the satellite images were validated by analyzing the data trend of synoptic stations in Tehran province using regression methods. Also, the trend of snow cover changes obtained from Terra satellite was compared with the trend of snow cover changes obtained from Aqua satellite by Kappa index. And the time series of these two satellites were compared by the correlation coefficient of Linear Modeling analysis. According to the results, changes in total days with monthly, annual and seasonal snow cover (autumn and winter) have a significant decreasing trend in a scattered manner in most parts of Tehran province. Seasonal trend analysis (STA) showed a delay in the start of days with snow cover and its shift from late January to late March. The correlation coefficient of MODIS sensor time series between two satellites in most parts of Tehran province was 99% and showed high similarity. Validation results showed that the trend of snow cover satellite images changes is 85% similar to the trend of synoptic stations snow cover data changes in Tehran province.

The climate of an area over a long period is called the climate. Climate identification and classification have long been of interest to meteorologists. Researchers have classified the earth into homogeneous climatic zones using different methods and climatic variables such as rainfall and temperature. They have used the results of climate zoning to assess water scarcity and water resources on a small and large scale to anticipate practical measures to control drought in vulnerable areas. The purpose of this study is to update and analyze the Spatio-temporal analysis of Iran's climatic classification based on the Domarten index and the Mann-Kendall test. Because in studies based on climate classification maps, up-to-date maps can better help understand the study area.

For this study, data related to temperature and precipitation variables were extracted monthly from 153 synoptic stations from 1995-2019 from the Meteorological Organization of Iran. First, the data of average annual temperature and total annual precipitation were obtained from monthly data and then, using isothermal and isothermal maps, were obtained using the kriging model. The final climate zoning map was prepared using the De-Martonne index based on rainfall and temperature. The non-parametric Mann-Kendall test was also used to evaluate the significance or non-significance of the De-Martonne climate index and determine the trend.

The results showed that based on the Kriging model, R2 and RMSE for precipitation data were 0.58 and 167.51 mm, respectively, and for the data were 0.83 and 2.23 ° C, respectively. This indicates better performance of the model for temperature data. This is related to the high variance of precipitation data in the country. Iran's climatic zoning based on the De-Martonne index showed six main climatic types in Iran. Most of the area of Iran is an arid climate and then a semi-arid climate. The study results showed that arid climate is 76.40%, the semi-arid climate is 19.65%, and other climates make up less than 4% of the area of Iran. Also, the area of arid and semi-arid climates with an area of 96.05% of the area of Iran has increased compared to previous research, which may be due to reduced rainfall and increased temperature. Also, the results of the Mann-Kendall test showed that Khorramdareh, Miyaneh, Ramsar, Boroujerd, Piranshahr, Tabriz, and Bijar stations have a significant upward trend (wetting trend), and Dezful, Malayer, Sabzevar, Bandar Anzali, Tehran (Mehrabad), Tehran (Shemiran), Qazvin and Dushan Tappeh stations have a significant downward trend (drying trend) at the level of 5%.

This study showed that Iran has six climatic regions, including; The climate is arid, semi-arid, Mediterranean, semi-humid, humid, and very humid. Also, comparing the results with the results of research done by other researchers in the past showed that the area of arid and semi-arid climates in the study period has increased compared to previous periods. Also, 14% of stations with a downtrend (8 stations) have a significant downtrend, and 7% of stations with an uptrend (7 stations) have a significant uptrend at 95%.

In this study, in order to investigate the trend of precipitation changes in Khuzestan Province, the data used were daily, monthly and annual data of precipitation of selected synoptic stations for a statistical period of 30 years (1987-2016). To study the trend of precipitation changes, precipitation-related indices defined by the ETCCDMI expert group were estimated using RClimDex software. Then, the ascending and descending trend of changes in precipitation limit values ​​was investigated using Mann-Kendall non-parametric test method. The age slope estimator method was also used to determine the rate of precipitation change. The results showed that all precipitation-related indicators (except for the number of days with more than 25 mm and very wet days) had significant changes at the level of 5%. In terms of stations, Dezful station with 26.41% had the highest rainfall and Shushtar station with 3.64% had the lowest rainfall. Behbahan station also had a 14.87% increase in rainfall.

One of the impacts of climate change is alteration in water cycles in the different parts of the world. Since the impacts can influence economy and importantly, human health, it is necessary to study effective parameters of human readiness against economic issues, water shortages and so forth in the future. Thus, the present research is conducted to study the process of hydro-climatic changes of Kan River basin. The research examined a 30-year period of 1985-2014 using Mann-Kendall test and linear regression. According to the research results, precipitation and discharge decreased slightly; whereas, evapotranspiration (evaporation and transpiration) followed an ascending trend. In addition, studying the changes within three prospective periods 2030, 2060, and 2090 through GISS-AOM of general circulation model series indicated that evapotranspiration maintains an ascending trend; while, precipitation declines despite volatility in particular periods. Moreover, the average temperature of the area, which is directly related to evapotranspiration, decreases to the mid21st century, and then increases comparing to global mean temperature.