تحلیل تغییرات بارش در شرق و غرب تراست اصلی زاگرس (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
اثر ارتفاع بر افزایش بارش و اثر ناهمواری بر ایجاد بیابان ازجمله مسائلی است که ذهن محقق را درگیر کرده است. هدف از پژوهش حاضر بررسی وضعیت بارش در دامنه های غربی و شرقی تراست اصلی زاگرس است. برای دستیابی به این هدف، عملکرد و ارتباط عوامل ارتفاع و بارش به عنوان پارامترهای مؤثر در دامنه های مختلف زاگرس بررسی و نقشه های هم بارش و هم ارتفاع از محدوده مطالعه شده استخراج و تحلیل شده است. نتایج نشان داد که افزایش بارش در دامنه های روبه باد با افزایش ارتفاع هماهنگی مطلوبی دارد؛ ولی افزایش بارش تا تراست اصلی زاگرس تداوم ندارد. در غالب مناطق، فراوانی بارش قبل از بالاترین ارتفاع زاگرس (منطبق با تراست اصلی زاگرس) اتفاق افتاده است؛ به طوری که با عبور از تراست زاگرس (باوجود ارتفاع چشمگیر منطقه) مقدار بارش به طور محسوسی روند کاهشی دارد. در قسمت های شمالی زاگرس بیشترین تغییر بارش در قسمت بادپناه (در مجاورت بلندترین قله ها) اتفاق افتاده است. دامنه های شرق تراست اصلی زاگرس، هرچند به دلیل موقعیت بادپناهی، بارش کمتری را دریافت می کنند، به علت شیب سطح های ارضی کمتر (نسبت به دامنه های غرب تراست اصلی زاگرس)، سطح دریافت کننده بیشتری دارند. همچنین، به دلیل مرتفع بودن، مقدار زیادی از بارش را به صورت برف دریافت می کنند؛ در نتیجه با فراهم شدن امکان نفوذ بیشتر آب به درون زمین (در طی دوره ذوب برف)، اثر های اکولوژیکی فراوانی را بر محیط پیرامون می گذارند.Estimate Precipitation Changes in the East and West of the Zagros Main Thrust
In relation to the effect of unevenness and precipitation, two issues have occupied the mind of researchers: First, the effect of altitude on increasing rainfall, and second, the effect of unevenness on the creation of deserts. The combination of these two effects has made it impossible to estimate a regression relationship between Zagros altitude and precipitation with a significant coefficient of explanation. The purpose of the present study is to investigate the precipitation situation in the western (rain-facing) and eastern (rain-sheltered) slopes of the Zagros main thrust and to create wind-sheltered (rain-sheltered) areas. To investigate the effect of the Zagros Mountain Range in the creation of sheltered areas, the function and relationship of the factors of altitude and precipitation were investigated as effective parameters in the creation of different slopes of this mountain range. Maps of both precipitation and altitude were extracted for the Zagros Mountain Range. According to the results obtained from examining the relationship between the maps of precipitation and altitude, it can be said that the increase in precipitation in the windward slopes has significant coordination with the increase in altitude, but the increase in precipitation does not continue until the main thrust of Zagros. In most of the regions, the maximum rainfall occurred before the maximum height of Zagros (corresponding to the main Zagros Thrust). When passing through the Zagros thrust despite the significant height of the region, the amount of precipitation has significantly decreased. In the northern parts of Zagros, the biggest change of precipitation has happened in the wind shelter part, in the vicinity of the highest peak. Considering the high altitude in the sub-basins to the east of the Zagros Thrust, as well as their lower slope compared to the basins located in the west, they receive less rainfall due to their sheltered position. But since they have more receiving surface and because of the high altitude, they receive most of the precipitation in solid form. More penetration of water into the ground is possible during the stages of snow melting. In addition, this phenomenon has considerable ecological effects.Keywords: Zagros Main Thrust, Wind Sheltered Desert, Dry Areas, Rain Shadow. IntroductionIran is a vast mountainous land that covers most of the plateau with the same name (Mahmoudi, 1988). The southwestern mountainous unit of Iran is known as Zagros, which limits the Iranian plateau from the west, southwest, and part of the south. Zagros ranges in the form of regular and similar strands form the largest unevenness unit of Iran (Zomordian, 2006, p. 209).In the heterogeneous spatial distribution of atmospheric precipitation and the formation of deserts, geographical conditions and especially the altitude factor play an effective role. How unevenness affects the received precipitation in mountainous areas is not a simple matter. Because in the first place, the gradient of precipitation is not the same in all the mountains of the country, and even in a certain mountain, the gradient of precipitation is not the same on the wind-facing (windward) slopes and the wind-back (shelter) ones. Another issue is that in all mountains, precipitation does not increase with increasing altitude, and in areas where the amount of precipitation increases with increasing altitude, this direct relationship does not continue to the top of the mountains and does not increase more than a certain height with the increase in rainfall. Finally, in addition to the complexity of the relationship between precipitation and altitude, there is a lack of measurement in high altitudes. The effect of unevenness on the precipitation situation is a definite principle; however, it cannot be firmly expected that by passing the high peak, the precipitation will decrease to the extent of desert formation. But investigating changes in the amount of precipitation in mountainous areas is always the concern of researchers. This study aims to investigate the precipitation situation in the western (rain-facing) and eastern (rain-sheltered) slopes of the Zagros main thrust and to create wind-sheltered (rain-sheltered) areas. Materials and Methods The information sources of this research include 1:50000 topographic maps, 1:100000 geological maps, a digital height model of Iran, and library resources. To conduct this study, the height of Zagros was determined according to its reflected border in Google Earth and ArcGIS. Then, climatic, rain gauge, and hydrometer stations were identified within the area and at a distance of 40 km from the studied area, and the required data were extracted from the recorded information of those stations. In order to investigate and analyze the climatic situation of the region, relationships were estimated between precipitation and altitude in each basin, and based on them, the isohyet of the Zagros Mountains was drawn. In order to investigate the effect of the Zagros Mountain Range in the creation of sheltered areas, the function and relationship of the factors of altitude and precipitation were investigated as effective parameters in their creation in different slopes of the Zagros. Maps of both precipitation and altitude of the study area were extracted for the Zagros Mountain Range. According to the axis of numerous descents and ascents of the Zagros Mountains, those areas that receive little rainfall under their influence were determined and the situation of wind-sheltered areas is also analyzed. Research FindingsTo better understand the variability of precipitation in the studied area, the precipitation and height profiles were drawn perpendicular to the main Zagros thrust line, which connects the highest peak of the Zagros Mountain Range from the north to the south of the Zagros Mountain Range. By drawing precipitation and height profiles, the general state of changes in height and precipitation in the axis of the Zagros Thrust has been depicted. The increase in precipitation in the windward slopes is coordinated with the increase in altitude, and this increase does not necessarily continue to the main thrust of Zagros. After crossing the Zagros Thrust, even without a significant decrease in altitude, the amount of precipitation has decreased to the easternmost part of Zagros. Such a situation indicates that the main thrust of Zagros actually corresponds to the border of the rain shadow areas. The west of it is covered by its rainy core, which is caused by the slope facing the wind. Despite the higher altitude in the east, the rainfall decreases due to the rain shadow.Discussion of Results and ConclusionIn general, unevenness has a mechanical effect on the incoming air masses. According to the results obtained from examining the relationship between the maps of precipitation and altitude, it can be said that the increase in precipitation in the windward slopes has a significant relationship with the increase in altitude, but the increase in precipitation does not continue until the main thrust of Zagros. In most of the regions, the maximum rainfall occurred before the maximum height of Zagros (corresponding to the main Zagros Thrust). When passing through the Zagros thrust despite the significant height of the region, the amount of precipitation has a noticeable decrease. In the northern parts of Zagros, the biggest change of precipitation has happened in the wind shelter in the vicinity of the highest peak. Due to the high altitude in the sub-basins to the east of the Zagros Thrust, as well as their lower slope compared to the basins located in the west, they receive less rainfall due to their sheltered position. But because they have more receiving surface and due to their high altitude, they receive most of the precipitation in solid form.
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