چکیده:
این تحقیق، با هدف پایش خشکسالی های هیدرولوژیکی در رودخانه دریانچای در یک دوره ی 31 ساله اجرا شـده است. مشخصات خـشکسالی های هیدرولوژیـکی شامل: زمان وقـوع، مدت، شـدت و حـداقل دبی مـشاهده شـده در طـول رخـداد خـشکی، از روش سـطح آسـتانه با نـرم افـزار NIZOWKA2003 محاسبه شده است. در اینجا، مقادیر سطح آستانه از منحنی مدت جریان انتخاب شده و دوره های ریز و وابسته دو سویه خشکی نیز با اعمال روش IC از سری رخدادهای خشکی مشاهداتی حذف شدند. تحلیل فراوانی براساس سریهای جزئی و با برازش توابع توزیعی مختلف برای بررسی احتمال وقوع رخدادهای خشکی، شدت و مدت آن صورت گرفته است. نتایج نشان داد در مجموع ۳۸ دوره ی خشکی هیدرولوژیکی در این رودخانه رخ داده که بیش از 60 درصد آن دارای تداومی بیشتر از 200 روز هستند. از نظر توزیع زمانی وقوع دوره های خشکی حدود 71 درصد (تعداد 27رخداد) در فصل بهار شروع شده است. در عوض، حدود 39 درصد (14رخداد خشکی) از مجموع خشکسالی های مشاهداتی در اسفندماه خاتمه یافته اند. بزرگترین رخداد خشکی، دارای تداومی577 روزه بوده و دومین دوره ی بزرگ خشکی با تداوم 365 روز با تاخیر دو ماهه رخ داده است. کسری جریان سطحی ناشی از وقوع دوره های خشکی در این رودخانه، معادل 117 میلیون مترمکعب محاسبه شده است. این موضوع و تعمیم آن به دیگر رودخانه های حوضه ی آبریز دریاچه ی ارومیه و تأثیر آن در کاهش سطح آب این دریاچه و خشک شدن آن بسیار حائز اهمیت است.
<strong>Introduction</strong> <br />Hydrological droughts occur after meteorological and agricultural droughts. In other words, this kind of drought is the final stage of the drought cycle and is affected by global climate change. Nowadays, many studies on hydrological droughts are based on the Threshold Level method, which is based on the Run Theory. According to this view, a drought is described as the length of a period in which hydrological variables, or discharges, are below the specified threshold level. To the researchers' knowledge, there have never been a major research on hydrological droughts in Iran and studies in this field are very limited in comparison with other types of droughts. Most of the researches in hydrological droughts have been done in the monthly and annual time intervals. However, the present study was conducted to investigate the hydrological droughts on a daily basis with the objectives of identifying and monitoring them and determining their occurrence and severity in the studied area. <br /><strong>Methodology </strong> <br /><strong>In this research, the Threshold Level Method was used to identify the hydrological droughts in the Daryan</strong><strong>Chai sub-basin in the northern part of Lake Urmia. Using the computer program NIZOWKA2003 based on the partial time series (PDS), the droughts in the hydrometric station of</strong> <br /> <br /><strong><br clear="all" /> </strong> <br /> <br /><strong>the Daryan during a thirty one year period (1982-2014) were calculated.</strong> <br />Hydrological drought characteristics including time of occurrence, duration, severity, and minimum observed flow during dry period were calculated based on <strong>the NIZOWKA2003 software. In addition, frequency analysis, probability of the number of drought occurrences, duration, and volume deficiency in different return periods were calculated using the mentioned computer program.</strong> Here, the threshold level was chosen based on the flow duration curve (FDC), which was based on the daily flow rates of the selected hydrometric station and prepared using the NIZOWKA2003 program. <br />The IC method was used to integrate the minor and mutual dependency periods of hydrological drought. Based on the characteristics of dry periods, the probabilistic distribution and frequency analysis of dry periods, the probability of the occurrence of drought and characteristics of dry periods (duration and volume deficit), fitting different types of statistical distributions and selecting the most suitable ones based on the fitting values (chi Score) were calculated using the NIZOWKA2003 computer program. <br /><strong>Results </strong> <br />The results of the calculations showed that a total of 38 periods of a hydrological drought occurred in this river. Approximately about 20 events from all detected drought occurrences lasted more than 200 days. The longest period of drought with 577 days lasted between the end of June 1988 and March 1990. Less than two months later, the second largest hydrological period with 365 days lasted between the beginning of May 1990 and the end of June 1991. Regardless of these two months, the largest hydrological drought period with 950 days was between 1988 and 1991. The severest hydrological periods were respectively 8987 and 6133 cubic meters, coincided with the largest hydrological drought periods. Moreover, the calculations showed that this river's water volume has fallen by 117 million cubic meters over the period of 31 years. <br /> <br /> <br />Based on the results of Chi-square test and Akaya's criterion, Poisson distribution was the most appropriate distribution of the probability of the occurrence of drought occurrence. Among the various probabilistic distributions, Weibull's distribution was the most appropriate distribution of the duration of the hydrological drought events. Accordingly, the probability of the occurrence of a dry period of at least 13 day duration is likely to occur in this river. Additionally, the maximum observation dryness event of 578 days was estimated with a probability of non-exceeding 0.99 % at the Daryan hydro-station. <br />The probable distribution of Weibull was selected as the most suitable distribution of the hydrological drought severity. Based on the Weibull method, the maximum water deficit volume was estimated at 13730 cubic meters with a low probability (0.01%). In contrast, the highest probability of the severity of drought (about 70%) in the Daryan Chai was estimated at 253,000 cubic meters. The results of the calculation of the return periods showed that in half of the cases, the probability of the occurrence of a dry period was with a duration of 170 days and an intensity of 2276 cubic meters with a 2-year return period. <br /><strong>Discussion and conclusion</strong> <br /><strong>Until the last decade, little research has been conducted on the hydrological droughts in Iran.</strong><strong>In very few studies, the analysis of the low flows from the point of view of frequency analysis has been addressed.</strong><strong>The lack or shortage of hydrometric data in many parts of the world has been the main limitation in hydrological drought studies. In this research, the Threshold Level Method was used to extract the</strong><strong>hydrological dry periods and their characteristics. Despite the fact that this method has been extensively used in drought studies, its selection is still one of the controversial issues in such studies. Using the daily time series can provide complete and accurate information from the start and end dates of drought events. However, the use of this time basis in drought studies, especially hydrological droughts, is not common in the world and in Iran.</strong><strong>The only studies in Iran, based on the daily time series, were conducted by Bayzidi and Saghafian (2011), Mesbahzadeh et al. (2017), and Mostafa Zadeh et al. (2018). Almost all other studies have been based on monthly or annual basis. </strong> <br /><strong>However, the use of a daily time series is often associated with the problem of having minor and</strong>mutual dependency<strong> periods. There are several ways to overcome this problem</strong>. The Interevent Critria.<strong> (</strong><strong>IC</strong><strong>)</strong><strong> is one of these methods which was used in this research.</strong><strong>The efficiency of this method has been previously reported by </strong>Zelenhasic<strong>and </strong>Salvai<strong>(1987), Hisdal et al. (2003), Tallaksen et al. (2004), and Baiziidi and Bayzidi and Saghafian (2011).</strong>
خلاصه ماشینی:
ون لوون ٧ (٢٠١٥: ٣٥٩) به بررسی ارتباط ویژگی های خشکسالی هیدرولوژیکی با اثرات و مسائل مربوط به مدیریت خشکسالی پرداخته و نتایج بررسی او نشان داد چهار چالش برای تحقیقات آینده در مورد خشکسالی هیدرولوژیکی تعریف شده اند که مربوط به ابتکارات بین المللی مانند هیأت 1- He 2- Yevjevich 3- sen 4- Guven 5- sharma 6- Spiliotis 7- Van Loon بین الدول تغییر آب وهوا (IPCC١) و "پانتا ری ٢" از انجمن بین المللی علوم هیدرولوژیک (IAHS٣) می باشند.
با استفاده از شاخص های استاندارد شده رواناب و بارش (SRRI١٠)، بررسی اثرات اصلاح بستر رودخانه و عدم انحراف غـیرمحلی آب بر روی روند و سـطح خشکسالی های هـیدرولوژیکی مورد بررسی قرار 1- Intergovernmental Panel on Climate Change 2- panta Rhei 3- International Association of Hydrological Sciences 4- Laaha 5- Regional drought area index 6- Drought Potential Index 7- Fleig et al.
, 2- Palmer Drought Index 3- Soil Moisture Model 4- Runoff sequence 5- Standardized Rainfall Index 6- Vegetation Health Index 7- Nyabeze Mujumdar و Mondal -٨ 9- Swetalina and Thomas 10- Truncation level ران ١ بنا گذاشته شده است .
در این تحقیق ، استخراج دوره های خشکی و مشخصات آن ، از روش سطح آستانه استفاده شده است .
این امر بیانگر آن است که در ایستگاه هیدرومتری دریان چای ، احتمال وقوع دوره ی خشکی هیدرولوژیکی با شدت یک میلیون مترمکعب و تداوم ١٠٠ روز ٩٠ درصد وجود دارد.
Hydrological Drought – Processes and Estimation Methods for Streamflow and Groundwater, Developments in Water Science, 48.