عنوان مقاله [English]
One of important conditions in time series data analysis is their stationary. If mathematical expectancy for a data series is independent with respect to the time, the mentioned series will be stationary. Since, the time series is often Non-stationary, it is necessary to recognize non-stationary agents and to remove them. One of the most important agents which conduct to create non-stationary in time series data is the trend component. Van Belle and Hughes (1984) studied homogenous of river Water quality trend Mann - Kendall non-parametric method. The use of mentioned method was a turning point in hydrology processes study. Lettenmaier et al (1994) studied the pattern of river flow rate trend. De Witt et al (2001) investigated the trend of rivers flow rates in Belgium. Their result study showed that in the recent century the trend of mean annual and seasonal discharge for studied rivers was increasing. Kahya and Kalayci (2004), studied the trend of river flow rate in 26 watershed in Turkey. Their results showed that in the most studied watersheds, the trend of rivers discharge was decreasing. They concluded that this decreasing trend can be explained by rainfall decreasing and temperature increasing. Wang et al (2005) investigated the trend of rivers discharges in west of Europe using Mann-Kendall method. Karla et al (2008) studied the trend of flow rate in united state. Birsan et al (2008) in the second half 20th century studied 60 rivers flow rates trend in Romania for period of 30, 40 and 50 years. They obtained the Relations between mentioned trends other parameters as temperature and precipitation change and physical properties. In their studies, watershed physical properties contained watershed area, average slope and height of the watershed, drainage channel density, watershed shape factor, average soil depth and other variables.
Due the Urmia lake depth decreasing, many problems have been formed about its survival and wild life. Investigation of Discharge volume, drought volume, and its return can be useful to prevent water depth falling. There the study of drought volume trend for Urmia lake Watersheds River can has an important role in this process.
In the recent research, the rivers daily discharge (m3 / s) in Western Azerbaijan province were used. Rivers drought volume was extracted and then the trends of obtained data were investigated.
Extraction of drought volume of daily river flow during durability
In this study, for determination or river Drought volume using daily flow rate, average annual method was used. The time series data of the daily river discharges were used 60 determine the drought duration disabilities. At first average annual for every day from a year was calculated. For example, f0r 1 January the equation (1) was used to determine average annual.
average year for 1th January=(Flow of 1th Jan for year 1977 +â¯..+Flow of 1th Jan for year 2011 )/(number of years) (1)
Then daily discharge was subtracted from average annual of the same say. With selecting the maximum of continues drought volume for 1 until n days, drought durations for mentioned periods were extracted. After these extractions, for years with lack data the time series was completed using regression method.
After extracting drought volume with spatial duration, the extract data were investigated and compared in the statistical period using Mann-Kendall, Spearman and Turning Point methods. The Value of z in Mann- Kendal and Turning points methods were tested in the 5% significance level and if the mentioned values are between - 1.66 and +1.96, the data will not have the trend (Safavi, 2009)....
The result of the drought Volume extraction for studied Rivers in Urmia Lake watershed showed that the pattern of the drought volume changes in different durability were similar each others, that a high correlation was obtained between different durability data. Therefore the trend investigation for a selected durability will be sufficient for the investigation of other durability. In the present research, One-day duration was selected as representative of other durability.
The results of trend investigation using Turning Point test showed that, the most Rivers in Urmia Lake watershed did not have one-day drought volume trend. But, this point was rejected according to the one-day drought volume graphs of Urmia Lakes Rivers and the mentioned graphs can be examined the graphs as a counterexample for turning points method. The results of the Mann â Kendall method showed that ther were non-significant increasing trend in drought volume rivers data in Mahabadchay, Gadarchay, Siminehrood, Zolachay and Rozehchay Rivers, and there were significant increasing trend in Zarinehrood, Barandozchay, Shahrchay and Nazloochaey Rivers. In this method (MK), no decreasing trend was obtained. The graphs of the drought volume Rivers data showed an increasing trend. Also, according to the drought volume Rivers data graphs and slope of the trend line in these graphs, it can be concluded that the Mann - Kendall provides more accurate results than the Turning Point method. Spearman's test results also confirmed method.
Due to result of the drought volume Rivers graphs and Mann- Kendall and turning points methods, can be concluded that the Turning Point method was not suitable method to study the River drought volume for Urmia Lake watersheds. For a better Survey and conclusion, Spearman test was added to the list of Trend methods. Spearman test also rejected the Turning Points results. The results of Mann - Kendall and Spearman methods were very similar each other. According to the graphs and using the obtained results of Mann - Kendall and Spearman methods, the mild increasing trend was observed in Zarinehrood, Shahrchay, Nazloochaey and Barandoezchay watershed. So that the mentioned watersheds can be seen as no trend watersheds. In Zolachay, Siminehrood, Gadarchay, Rozehchay and Mahabadchay Rivers, increasing trend in drought volume Rivers were observed. The results also indicated that the increasing trend in volume Drought River for was occurred and the North-West of the Urmia lake, that this due showed that decreasing trend in the daily discharge data for this area.