مقایسه تاثیر تغییرات روند کاربری اراضی و بارش بر دبی سالانه (مطالعه موردی حوزه آبخیز کیار)

توسعه مناطق شهری و کشاورزی و بهره برداری بیش از حد از منابع طبیعی به منظور برآورد نیاز روز افزون انسان ها باعث ایجاد تغییرات چشمگیری در رژیم هیدرولوژیکی حوزه های آبخیز می شود. همچنین، تغییر عوامل اقلیمی از قبیل بارش از مهم‌ترین دلایل تغییرات دبی رودخانه ها است. بررسی همزمان تغییرات عوامل اقلیمی و کاربری اراضی در ارتباط با تغییرات دبی رودخانه از اهمیت بالایی برخودار است. هدف از این تحقیق بررسی روند تغییرات کاربری اراضی و بارش و نقش هر یک آن‏ها در روند تغییرات دبی حوزه آبخیز کیار در استان چهار محال و بختیاری است. بدین منظور ابتدا برای تحلیل روند سری‏های زمانی بارش و دبی از روش ناپارامتریک من کندال استفاده شد. سپس با استفاده از تصاویر ماهواره لندست مربوط به سال‏های 1990، 1999 و 2009 و با استفاده از روش شیءگرا در محیط نرم افزار idrisi taiga اقدام به تهیه نقشه کاربری اراضی حوزه شد. نتایج تحلیل روند برای سری زمانی دبی رودخانه در ایستگاه کوه سوخته نشان داد که دبی در مقیاس های فصلی و سالانه روند کاهشی داشته است. بطوری که بیشترین روند دبی در سری فصلی در فصل تابستان و کمترین روند دبی در فصل پاییز ثبت شد که در سطح 1 درصد معنی‎داری بودند. نتایج بررسی روند در سری زمانی بارندگی های منطقه، دارای رفتار متفاوتی بود بطوری که در ایستگاه بروجن روند افزایشی و در ایستگاه های شهرکرد و بهشت آباد روند کاهشی و در ایستگاه فارسان بدون روند قابل تشخیص مشاهد گردید. نتایج حاصل از بررسی روند تغییرات کاربری نشان داد که اراضی مسکونی و کشاورزی، روند افزایشی و اراضی مرتعی و بایر روند کاهشی داشته اند. با توجه به روند تغییرات کاهشی بارش و همچنین افزایش اراضی بایر و اراضی مسکونی، نتیجه گیری می شود که تاثیر تغییرات بارش بر میزان دبی بیش از تغییرات کاربری اراضی است.

comparison of the effects of land use change and precipitation on annual discharge (case study: kiar watershed)

extended abstract introduction the development of agricultural and urban areas and overexploitation of natural resources have caused significant changes in the hydrological regime of watersheds. furthermore, population increase, unprincipled exploitations and climate changes have intensified this process. it is therefore necessary to know and study it continuously. the trend of hydrological series may also change due to climate change, land use and watershed management. therefore, identifying the presence or absence of changes in time in rainfall and discharges of an area and presenting it in statistical analysis seems necessary. the mann kendall test is one of the most widely used nonparametric methods for analyzing the flow of such data. studying periods of rainfall and discharge as well as land use change can be useful in expressing the role of climatic and human factors. therefore, the present study was conducted to investigate the trend of land use change and the role of each in the discharge trend of kiar watershed. materials and methodsthe present study was conducted in kiar watershed located in chaharmahal and bakhtiari province as one of the northern sub basins of karun river. in order to conduct the current research and achieve the desired goals, after obtaining the information and data required for the research from the chaharmahal and bakhtiari regional water organization, a joint statistical course of study stations was determined. finally, the mentioned period was selected from 1363 1390. then, mann kendall non parametric test was used to investigate the trend of changes in precipitation and discharge of stations in kiar watershed. then, land use changes in the study area in three time periods were extracted using the object oriented classification method in idrisi taiga 16.03 software environment using landsat’s tm sensor images. using the parameters of overall accuracy and kappa coefficient, the accuracy of the classification was calculated. finally, the trend of land use change and its relationship with the trend of discharge were evaluated.results and discussionthe results of trend analysis for the dey river time series (on seasonal and annual scales) at the burnt mountain station show that discharge has had a decreasing trend on both scales. the highest discharge trend in the seasonal series belongs to summer and the lowest discharge trend belongs to fall at the significant level of 1%. the study of trends in the rainfall time series of the region shows a different behavior. while the trend in borujen station was upward, shahrekord and beheshtabad exhibited a downward trend, and no trend was found in farsan station. the decreasing trend of discharge and precipitation in kuh e sokhteh hydrometric station and rain gauge stations in shahrekord and beheshtabad are on the same side, which can be attributed to the decrease in discharge due to the rainfall behavior of the region. the results of the trend of land use change showed that residential and agricultural lands have an increasing trend and rangeland and barren lands have a decreasing trend. increasing the level of agriculture and residential areas can be a reason for reducing the trend in discharge.conclusionbased on the results of the present study, the results of trend analysis for the time series of the river at the burnt mountain station showed that the discharge trend in seasonal and annual scales is downward. the highest discharge trend in the seasonal series belongs to the summer season and the lowest discharge trend belongs to the autumn season. also, the results of studying the trend in the time series of rainfall in the region showed different behaviors. while, the trend in borujen station was upward, shahrekord and beheshtabad exhibited a downward trend, and no trend was found in farsan station.