ارزيابي اثرات تغيير اقليم بر مقادير رسوب معلق در تعدادي از حوزه‌هاي آبخيز استان اردبيل

The Effects of Climate Change on Runoff and Suspended Sediment Values in Some Watersheds of Ardabil Province

برآورد رسوب‌دهي رودخانه‌ها به‌دليل تأثيرگذاري عوامل مختلف داراي پيچيدگي بالايي مي‌باشد. اﺳﺘﻔﺎده از ﻣﻨﺤﻨﯽﻫﺎي ﺳﻨﺠﻪرﺳﻮب و راﺑﻄﻪ ﺗﻮاﻧﯽ ﺑﺮازش داده ﺷﺪه ﺑﯿﻦ دادهﻫﺎي دﺑﯽ و ﻏﻠﻈﺖ رﺳﻮب ﻣﻌﻠﻖ ﯾﮑﯽ از ﻣﺘﺪاولﺗﺮﯾﻦ روشﻫﺎي ﺗﻌﯿﯿﻦ ﻣﯿﺰان ﻏﻠﻈﺖ رﺳﻮب ﻣﻌﻠﻖ اﺳﺖ. هدف پژوهش حاضر به‌‌دست آوردن تغييرات رسوب طي دهه آينده (2030-2011) با استفاده از معادله سنجه‌رسوب مي‌باشد. براي اين‌منظور از مدل هيدرولوژيكي IHACRES و مدل اقليمي LARS-WG استفاده شد. مدل IHACRES ابتدا براي 7 ايستگاه هيدرومتري واسنجي و اعتبارسنجي شد سپس با به‌كارگيري مدل LARS-WG ميزان تغييرات درجه حرارت حداقل، حداكثر و بارندگي براي دوره آينده به‌دست آمدند. اين تغييرات به مدل IHACRES اعمال شدند و ميزان دبي جريان دوره آتي تخمين زده شد. با استفاده از داده‌‌هاي دبي و رسوب مشاهداتي منحني‌سنجه‌رسوب تهيه و مقادير دبي رسوب معلق براي دوره آتي محاسبه شد. نتايج نشان داد مقدار بارندگي 3/68 درصد كاهش يافته و دماي حداقل 16/48 و دماي حداكثر نيز 5/39 درصد افزايش يافته است، كه به‌طوركلي منجر به كاهش 16 درصدي رواناب شده‌است. همچنين تعداد رخدادهاي دبي اوج افزايش يافته كه بيش‌ترين افزايش مربوط به ايستگاه هيدرومتري يامچي با دبي متوسط 2/09 و 16 رخداد دبي اوج بالاي 6 مترمكعب برثانيه مي‌باشد. اين تغييرات اقليمي به‌طور متوسط منجر به كاهش 47 درصدي بار معلق رسوب در ايستگاه‌هاي مطالعاتي شده‌است. نتايج پژوهش نشان دهنده تأثير قابل توجه تغيير اقليم بر حوزه‌هاي آبخيز استان اردبيل مي‌باشد و با توجه به اثرات زيست محيطي تغيير اقليم لازم است راهكارهايي جهت مديريت مناسب حوزه‌هاي آبخيز اتخاذ شود.

Estimation of the rivers sediment load has high complexity due to effecting different parameters in this aspect. Regarding the power relationship between discharge data and suspended sediment load use of sediment rating curves is one of the most common methods for determining the sediment yield in ungauged watersheds. Sediment condition shows the upstream characters and using the obtained data makes a relationship between erosion and sediment load. The different parameters such as climate, land use, data accuracy, and the applied methods have an effect on the sediment rating curve shape. Agriculture activities such as tillage in the direction of slope lead to accelerated erosion in the watersheds, especially in the Mediterranean area. These decades many studies assessing the effects of climate changes in the future period and it affects runoff. In this study, the main objective is to obtain sediment changes during the future decade (2011-2030) using the curve rating in sediment estimating. For this purpose, the IHACRES hydrologic model and the LARS_WG climate model were used. Material and Methode The IHACRES model for seven hydrometric stations was calibrated and validated. This model is rainfall and runoff erosion that require a little data for running including minimum and maximum temperature, rainfall, discharge and study are. This model defined as a lumped model and highly common in watersheds with scarce data. With running this model in all of the models the model parameters were calibrated. Also, the LARS_WG model was used for determining the weather changes that are occurring in the Samian watershed. This watershed has near to 4 thousand square kilometers that have many sub-watersheds. In this study, the watersheds in the west of the Samian watershed were selected for modeling. The average of rainfall in this area is between 220 and 457 mm, and the weather temperature changes in this region are high and that is between -32 to 34 C°. The results of LARS_WG showed the weather changes in each part of the hydrological model inputs that these changes were applied to the IHACRES model and the discharge flow rate was estimated for the future. On the other hand, using the observed discharge and sediment yield were calculated the sediment curve rate. By changes in flow discharge at the study stations, were calculated the suspended sediment discharges for the future period. results and discussion The results of the LARS_WG model showed that the amount of precipitation decreased to 3.68 percent and the minimum and the maximum temperature increased by 16.48 and 5.39 percent, respectively. Decreasing the input precipitation in most parts of the world particularly in Iran watersheds mentioned in many studies. One of the other the most important effect of climate change in this area is minimum and maximum temperature increase that leads to evapotranspiration increasing and soil moisture loss. The results of the IHACRES model showed that this model has a suitable capability for simulation runoff in the study area, therefore, it was used for estimating the future runoff regarding climate changes. The model output showed that during the next decades the average flow rate in the hydrometric stations will decrease by a total of 16 percent and the number of peak flood events will increase, that the highest increase between the study watersheds observed in the Yamchi hydrometric station with a mean of 2.09 m3s-1 and 16 peak events with over 6 m3s-1. Using the obtained results of the climatic model, hydrological model and the sediment rating curve the suspend sediment changes were estimated for the future period. The result shows that these climatic changes will lead to a 47 percent reduction in the average suspended sediment load at study stations. Conclusion The consequences of climate change have a significant effect on water resources quality and quantity. The aims of this study were to calculate the weather changes and it's ruling on discharge and sediment yield changed. the results of this study indicate the effect of climate change on the Ardabil province watersheds is remarkable. Considering the environmental impacts of climate change and dependence on human life on the environment it is necessary to implement an appropriate approach for decent management in Watersheds.