جستجوی مقالات مرتبط با کلیدواژه « sen’s estimator » در نشریات گروه « آب و خاک »

Detection of trends in streamflow characteristics such as low flows is so important in optimal water resources management. This is especially true in arid and semi-arid climates that water is vital for human being and all other living things. Lorestan province, located in the west part of Iran was considered as the study area. Daily mean streamflow data of hydrometric stations during the time period provided by Lorestan Regional Water Company located in Khorramabad city. Eight hydrometric stations selected for this purpose. The altitude of the chosen stations varied between 770 and 2050 m above the mean sea level. Literature review on this subject indicated that low flow trends in Lorestan province river has not been before studied. On the other hand, such a study is so important for better management of fresh water in the region, therefore, conducting this study seems to be necessary.

In the first step of this study, flow duration curves (FDC) plotted for the stations. Two indices including the Q0.05 and Q0.10 were considered here as measures of low flows. The Q0.05 index value extracted from the FDC as a five percent low flow quantile. This index shows that the streamflow discharge is less than that in five percent of the days in a year. In addition to Q0.05 the second measure namely Q0.10 is read from FDC of the selected sites. Therefore, for each site, these two indices were gathered during the used time period. Then, trends of the mentioned indices are analyzed using the Mann-Kendall method. In this regard the effect of serial correlations removed from the time series. Moreover, the slope of trend lines estimated using the Sen’s estimator approach. Then the selected quantiles fitted for suitable statistical distributions. In this regard the well-known method namely Kolmogorov—Smirnov was used.The parameters of the selected distribution estimated using the maximum likelihood method. Finally, at each site the values of low flows corresponding to different return periods i.e. 2, 5, 10, 25 and 50 years were estimated. It is worthy to mention that the missing data are not reconstructed here, because the used approach (Mann-Kendall) is a non-parametric method and no need for reconstruction of the missed values.

Results showed that two stations namely Sokaneh-Nahaee and Cham-Chit had significant first-lag serial correlation for Q010 time series. The other six sites had no significant serial correlation for this quantile. Furthermore, in the case of Q0.05, three sites showed significant first-lag serial correlations. So, the modified Mann-Kendall method was used for these time series. This analysis indicated that the mentioned series auto-correlation was significant in 5% level. The conventional MK method was used to detect trends in other time series which their serial correlations are not significant. Results showed that trends of Q0.10 quantile series in four out of the eight hydrometric stations were downward and two of them were statistically significant at 1% level. The two others had no significant trends. At the same time the other sites showed upward trends in Q0.10 series. However, among these series one station namely Cham-Chit had statistically upward trend at 1% level. Trends in the other three sites are not statistically significant.  In the case of Q0.05 series, the six out of the eight stations showed negative trends, in which two sites had statistically significant trends at 1% level. The names of these sites are Sokaneh-Nahaee and Vanaee. In contrast, the two other time series showed positive trends, in which only one of them (namely Cham-Chit station) had statistically significant trend at 1% level. The trend line slopes of Q0.10 quantile time series are ranged between -0.0844 (in Sokaneh-Nahaee) and +0.12 (in Cham-Chit). However, in the case of Q0.05, this range was between -0.0885 (in Sokaneh-Nahaee) and +0.008 (in Cham-Chit station).

Some of the stations showed upward trends in low flows in Lorestan province rivers and some others showed downward trends. It is worthy to note that the time periods of the used data of the stations are not same. Although Masih et al. (2011) reported that the mean daily stream flows (i.e. Q0.50 or 50th quantile also called median) of Zagros Mountain rivers had downward trends. Investigation of sites location indicated that no obvious pattern in trends of low flows existed in the area under studied. This is true for both two low flow indices (i.e. Q0.05 and Q0.10) used for hydrometric stations. The findings of this study would be helpful in better management of surface water in Lorestan province.

Urmia Lake is one of the largest hypersaline Lake in Iran which its capacity is about 32 MCM in its normal condition. In recent years, climate change and decreasing rainfall led to falling water level in the Lake. Although, due to its high salt concentration this fall in water level led to extending areas of saline lands around the Lake. Furthermore, drought occurrence and rainfall decreasing trend cause solute concentration to be increase in the Urmia Lake water. For logical and scientific management of fresh water in Urmia Lake Basin it is necessary to investigate the trends of different characteristics of daily rainfall. The aim of this study is to detect trends in the number of days with different rain depths in five distinct classes in Urmia Lake basin. In order to detect trends the information of the twenty five stations having at least 10 years consecutive daily rainfall data were used. Trends of time series detected using the non-parametric Mann-Kendall method. Moreover, slope of trend lines estimated by using the Sen's estimator approach. In order to analyze the spatial trends for each of the time series some relevant maps prepared in which, the stations having significant trends were shown by markers. This facilitate the interpretation of trends in the area under study. The results showed that the slope of trend lines for days having rainfall less than 1 mm is often positive. About 84% of the stations had upward trend line. The five stations located in the southern part of the basin experienced (in level of 10% or less) significant upward trend in the number of days with precipitation less than 1 mm. The slope of trend lines in the case of the days having rainfall depth between 1 and 5 mm were almost negative. In the case of days with rain between 1 and 5 mm, the 15 stations had downward trend lines, which five of them showed significant trend, whereas the remaining stations had upward trend line slops (insignificant at 10% level). On the other hand, the slope of trend lines for the number of days with rainfall between 5 to 10 (mm) in 44% of the stations were negative in which, only four of them were significant (in 10% level). Trend line slopes in 40% of the station were positive, in which only one station experienced significant trend at ten percent level. The steepest positive trend magnitude belonged to the station namely Herris with β = 1. 633 (day/year). For the number of days with precipitation between 10 and 15 mm about 32% of the stations had negative trend line slopes, in which only three stations experienced negative significant trend. About 26% of stations had positive trend line, in which only one section (namely Maraghe) exhibited significant trend in 1% level. The steepest slope of the trend lines was related to station Shahindezh with β = 0.585 (days/year). The slope of trend lines for the number of days with rainfall more than 15 mm were positive for 52% of the stations, in which only one of them experienced significant trend (in 10% level). Moreover, 24% of the stations had negative trend in the mentioned class. Out of the total 25 selected stations only one section (namely Maraghe) had significant negative trend. The steepest slope of the trend lines belonged to the station Herris with β = 0.464 (days/year). In general trends of the number of days having rain depth less equal one mm in Urmia Lake basin was upward. But trends for the time series of the number of days having rainfall in the classes of 1-5, 5-10 and 10 -15 mm were downward. This means that light (shower) storms events in the study area is going to be occur frequently but heavy rains is going to be rare. It can be concluded that the number of light raining days had increasing trend. This implies that such light rains can not to be used for crops and trees. Because such rains immediately lost by evaporation proses after ceasing the rain. On the other hand, heavy rains which showed increasing trends for most of the selected station might be crate huge floods in the rivers flowing into the Urmia Lake Basin.

In this study, the temporal and spatial variation of snow depth over the mountainous region of Zagros, in the western Iran, for the period 1979–2010 was investigated for the cold season when the probability of snow occurrences was high. For this purpose, daily gridded snow depth data relative to Era-Interim/land were retrieved from the European Centre for Medium-Range Weather Forecasts (ECMWF) and used for spatiotemporal analysis of snow in the region. Furthermore, monthly maximum, minimum and mean air temperature relative to the weather stations distributed over the region were also used to investigate the relationship between snow depth and air temperature variability in the region. In each grid point, the rate of temporal changes in the snow depth was estimated using the Sen’s slope estimator, while the modified Mann-Kendall Test was applied to assess if the change identified was statistically significant. The results showed that in almost all of the studied months, especially February and March, the snow depth was significantly reduced in the region, which was statistically significant at 5% significant level. Unlike the observed statistically significant decreasing trend in the depth snow in the region, a significant increase in the maximum, minimum and average temperature was observed for all the studied months and the stations. The result suggested that the observed decrease in the snow depth in the region was related to the increasing trend in the temperature during the study period, which could be attributed to the global warming and climate change.

Studying the trends of water table in any region especially in arid and semi-arid regions is an important issue. This study focuses on assessing groundwater table changes in Tabriz plain. For this purpose, non-parametric Mann-Kendall test is used. In studing groundwater level the information of 14 pizometric wells in the period of 1991-2013 was used. Significant levels of 1, 5 and 10% were used for the trend test. Slope of trend lines is estimated using the sen's estimator method. The homogeneity of trends were tested using the Van Belle and Hughes method. The results showed that groundwater level in the most of pizometric wells have decreasing trend, That was significante in 1% sifnificance level. According to the research, trend of groundwater level was negative in all of the stations in April and maximum negative trend was belong to Dizaj Leily Khany station (Z= -6/47) that was significante in 1% sifnificance level. Also the minimum negative trend was belong to Ana Khaton station (Z= -0/322). The minimum groundwater level was -1.45 in Said-Abad station.

In this study, the values of ET0 were estimated using the Penman-Monteith method for nine stations located in Lake Urmia basin over the 1986-2010 period. In order to detect the trends of reference crop evapotranspiration (in monthly, seasonal and annual time scales) the non-parametric Mann-Kendall (MK) statistical test was used. The Sen's estimator was used to evaluate the trend line slope of time series. The results showed that in the annual time scale six time series (66.6%) had significant (p

In the world, groundwater resources are counted the second freshwater resources after polar glaciers. Investigating changes in groundwater levels in any region has an important role in planning and sustainable water resources management. Continuous decline of groundwater level has been observed in many places of the world in the past half-century. It has indicated the depletion of groundwater reserve in large scale. This reserve depletion has been caused either by over-exploitation or reduction of groundwater recharge. In the recent years, groundwater use has continuously increased to meet demand for expanding industrial, agricultural and urban water supply. Meteorological parameters changes exert extra pressure on further reduction of groundwater level. Since, until now, the comprehensive studies about trend changes of ground water level have not accomplished in Urmia region therefore the main goal of the present research is to investigate the changed trend of Urmia ground water level using Mann-Kendal non-parametric method.
The study area has located at 55° 10´ 26" longitude and 37° 4´ 12" latitude in northwest of Iran. For studied region, the mean annual precipitation is 304 mm and its climate is dry and cold. This plain located in west part of Urmia lake in west Azarbayjan. In the present research, trend analysis was conducted on groundwater level of 31 piezometeric stations in the monthly and annually scales in the period of 2002-2011 using Mann-Kendall non-parametric test. Data Analyze was carried out using the boxplot software in SPSS. Trend line slope was estimated by using Sen’s estimator for each time series. Homogeneity of trend was tested using the Van Belle and Hughes method.
The results showed that the trend of groundwater level for all stations was negative and the negative trend in 1% probability level was significant for 56 percent of the stations. The investigation of trend line slopes revealed that in average, the groundwater level of Urmia plain has been decreased about 19.9 cm/year. Also, the results of homogeneity test of trend in 5% probability level showed that the trend was non-homogeneous for different months and heterogeneous for various stations.
According to the obtained results from the present research, the changes trend of the region ground water level is negative. If the exploitation from ground water resources continues in the present form, social and economic crisis can be formed. According to the results of this research, it is necessary to control the ground water exploitation and ground water level will be increased by increasing agricultural water efficiency and artificial recharge.

Groundwater qualitative changes trend of Miandoab Plain (in the wet and dry periods) in the period of 1992-2012 was analyzed using the non-parametric modified Mann-Kendall test for lag-1 autocorrelation cofficient. The results showed that among the 25 sampling stations for 14 water qualitative variables، about 58% of the series had significant (P 5%) increasing trend. Also 32% of them showed significant decreasing trends. The remaining 10% of the series exhibited no trend at the 5% significant level. In the case of the wet period 23. 7% of the series exhibited upward significant trend and 6. 3% of the series had significant decreasing trend at the 5% level. About 70% of the series showed no trend (at 10% significant level). In the dry period، 22% of the series had significant increasing trend (at 10% level)، 10% with decreasing trends and 68% of them had no significant trends. The results showed that in the wet period، the steepest increasing trends of groundwater qualitative variables were observed in the west and southern part of the Miandoab Plain. The declination of groundwater level led to increasing trends for water qualitative parameters in the eastern part of the plain. The results of Sen’s slope estimator showed that، the EC and SAR had increasing trends for the both dry and wet periods. For example، the trend line slope of the groundwater EC for the wet period was equal to 20 µS cm-1 year-1.

In this study, in order to analyze the changes trend of the crop water requirement as the aspect of climate change in East Azerbaijan, we have adopted FAO Penman- Monteith reference crop evapotranspiration and 15 variables associated with it. By using nonparametric methods of Spearman, Man- Kendall and Sen’s Estimator in twelve monthly and annual series for each station, the trends have been explored. The results of these two test statistics indicate that the significance of the respective phenomenon is being studied in two separate clusters. The first cluster consists of Tabriz and Maragheh stations the entire time series, the time series exceptions of April in Tabriz, the rest of the series with the significant increase in confidence levels are 95% and 99%. The second cluster consists of Ahar, Sarab, Mianeh and Julfa stations that mentioned phenomenon of jointly in the time series in March with a significant increase in the same levels of trust. Also the test results from other variables show that despite a series of meteorological variables, no significant trends were, but due to the influence of the reference crop evapotranspiration and the significant impact it has on the superposition. Finally, we should acknowledge that the study of climate change in the region, is not just dependent on the climate variables and could be caused by other variables too.

Modeling of water table depth fluctuations because of uncertainity in its parameters is rather complicated and was studied in the current work. For this purpose temporal variability of water table depth at 22 piezometric wells and precipitation data at 3 rainfall stations in the Malayer plain were evaluated from 1989 to 2007. Trends in data series of monthly, seasonally and annually with Sen's estimator nonparametric method was calculated and interpreted based on the defined constraints and trend start time by using Mann-Kendall test. The results showed that at monthly time scale 79.5% of the wells had significant positive slope. The remaining 16.3% had positive and 4.2% negative slope. At seasonal time scale 80.7% of trends had significant positive slope; 14.8% of the rest encountered with positive and the remaining 4.5% with negative slopes. At the annual time scale, analysis indicated that the trend in 81.8% of the wells was significant with positive slope. The tredn in 13.6% was non-significant with positive slope and the 4.6% was negative. Overally, the trends of piezometerc wells showed rapid decreasing in the water table depth at the sudied area and presenting unwise utilization of the ground water resources in the area.