نوع مقاله : مقاله پژوهشی

نویسنده

• سید حسین میرموسوی

دانشیار اقلیم شناسی ، گروه جغرافیای دانشگاه زنجان

چکیده

خشکسالی یکی از مهم ترین مخاطرات اقلیمی است که تأثیرات زیادی بر بخش های مختلف طبیعی و فعالیت های انسانی دارد. از مهم ترین اثرات خشکسالی تأثیر آن بر کاهش آب های سطحی در حوضه های آبریز است که نهایتاً با کاهش ورودی رودخانه ها به دریاچه ها، سبب خشک شدن تدریجی آنها می شود. بر این اساس در پژوهش حاضر سعی بر آن شده است تا اثر خشکسالی بر روی دریاچه های بختگان، طشک و مهارلو استان فارس در طی دوره 2021-2000 مورد بررسی قرار گیرد. برای این منظور از تصاویرماهواره لندست 5 تا 8 استفاده شده است. هم چنین به منظور پایش خشکسالی از شاخص پالمر استفاده شده است و بر اساس این شاخص فراوانی و شدت وقوع خشکسالی در ایستگاه های منتخب برای هر سه دریاچه استخراج شده است. به منظور برآورد مساحت دریاچه ها، از شاخص استخراج خودکار آب (AWEI) بهره گرفته شده است. نتایج حاصل از ارزیابی خشکسالی نشان می دهد که در 22 سال مورد مطالعه، در دو ایستگاه منتخب طشک و بختگان 15 سال و در ایستگاه منتخب مهارلو 14 سال خشکسالی با شدت های مختلف اتفاق افتاده است. طولانی ترین خشکسالی با تداوم 6 ساله بین سال های 2008 تا 2013 به وقوع پیوسته که در این دوره سطح آب دریاچه ها به شدت کم شده است. تحلیل تغییرات سطح آب در این دریاچه ها نیز نشان داد که بیشترین مساحت دریاچه ها را رودخانه های فصلی به خود اختصاص داده اند. این موضوع نشان می دهد سطح آب این دریاچه ها به شدت از بارش های فصلی تبعیت می کند. در بررسی تصاویر ماهانه نیز مشخص شد در هر سه دریاچه سطح آب فصلی در بین ماه های آبان تا اردیبهشت افزایش پیدا می کند. میزان ماندگاری آب فصلی نسبت به سال های مختلف در دریاچه ها متفاوت بوده ولی میزان آن به طور کلی بین 3 تا 7 ماه است.

کلیدواژه‌ها

• خشکسالی
• شاخص پالمر
• دریاچه های بختگان
• طشک و مهارلو

موضوعات

• استخراج، پردازش، تولید و نمایش داده های جغرافیایی

عنوان مقاله [English]

Analysis the effects of drought on water level changes in The Bakhtegan, Tashk and Maharlo lakes

نویسنده [English]

• Seyed Hossein Mirmousavi

Associate professor of climatology, Zanjan University

چکیده [English]

Extended Abstract
Introduction
In hydrological drought, water scarcity spreads through the hydrological cycle and can subsequently reduce groundwater levels, surface water and lake levels, and this means that hydrological drought dominates those areas, leading to long-term effects. In addition, due to climate changes and rainfall and temperature anomalies, droughts have increased in frequency and severity in many regions of the world. The predicted changes for the coming years show that climate variables will not have uniform changes in all regions and regional changes in the amount of precipitation may lead to the creation of hydrological patterns much different from the current conditions.
The present study was also carried out with the aim of spatial analysis of drought effects on water level changes in the catchment area of Bakhtegan, Tashk and Maharlo lakes. In this research, an attempt has been made to identify temporal and spatial patterns of changes in the level of this lakes by using satellite images and spatial analysis models.
Materials and Methods
In the present study, Landsat 5(TM), 7(ETM+) and Landsat 8(OLI) satellite images with a resolution of 30 meters have been used in the period of 2000-2021 to investigate water level changes. Due to the fact that the water level of the studied lakes changes drastically with the rainfall of different months, therefore, it is difficult to determine the amount of water cover for a year without considering the fact that a part of this cover is seasonal and when the rainfall decreases, a part of the lake Dry may not provide accurate results. Based on this, in the present study, one image was used for each month for each year studied to evaluate the changes in the water level of the lakes in all months of the year.
Conclusion and Discussion
The investigation of the changes in the water level of Maharlo Lake shows that in the drought of 2108 and 2017, the permanent water level of the lake has decreased to 1.8 square kilometers. Meanwhile, in the severe and very severe drought of 2005 and 2004, the permanent water level reached 170.4 square kilometers. Examining the changes in the area of Tashek Lake in 15 years of drought shows that the area of the waterless part of this lake has increased more than the seasonal and permanent water. The highest amount in this field was in 2021 with a very severe drought, which shows that this lake has more critical conditions in terms of permanent dryness than Maharlo Lake. This lake has been in a terrible state for 5 years. Comparing the changes in the area of Bakhtegan lake in different years shows that this lake has a more critical situation than its neighboring lakes (Maharlo and Tashk), so that in a significant number of years (12 years) the lake lacked permanent water and only With monthly or seasonal rains, some water has been temporarily collected on its surface, but it has a short shelf life between 2 to 6 months (November to May).
Results
The results of the evaluation and analysis of the role of drought in the water level changes of the Bakhtegan, Tashk and Maharlo catchment lakes showed that the area of these lakes has decreased significantly during the studied period, so that over time the area of the water area has decreased. It has been permanently reduced and added to the dry and waterless area. The maximum decrease in the water level of all three investigated lakes occurred during a 6-year drought between 2008 and 2013, in such a way that the area of the part with permanent water was greatly reduced and the area of the dry part of the lakes was increased.

کلیدواژه‌ها [English]

• Drought
• Palmer index
• Bakhtegan
• Tashk and Maharlo lakes