با همکاری انجمن آبخیزداری ایران

نوع مقاله : مقاله پژوهشی

نویسنده

استادیار، پژوهشکده حفاظت خاک و آبخیزداری، سازمان آموزش، تحقیقات و ترویج کشاورزی، تهران، ایران

چکیده

افزایش گازهای گلخانه‌­ای ضمن تاثیر بر روی عناصر آب و هوایی، سامانه­‌های متاثر از این متغیرها، نظیر منابع آب، کشاورزی، محیط زیست، بهداشت و اقتصاد را نیز دگرگون می‌­سازد. تغییر آب و هوا، با ایجاد تغییرات در چرخه هیدرولوژی باعث اثرات معنی­داری در منابع آب می­‌شود. برای بررسی تغییرات آب و هوا در آینده، روش‌­های مختلفی وجود دارد که مهمترین آن‌­ها مدل­‌های اقلیمی هستند. مدل­‌های گردش کلی جفت شده (AOGCM) متغیرهای اقلیمی را در وسعت چند ده هزار کیلومتر مربع شبیه‌­سازی می­‌کنند، اما قادر به شبیه‌­سازی فرایندهای منطقه‌ای و کوچک مقیاس آب و هوا نیستند. برای رسیدن به این مهم، از روش­‌های ریز­مقیاس‌نمایی استفاده می­‌شود که یکی از مهمترین آن­‌ها روش‌­های دینامیکی می­‌باشد. این روش، مبتنی بر بالا بردن قدرت تفکیک و تجزیه هرچه بیشتر مدل­‌های گردش کلی هستند. در این مطالعه، به بررسی اثرات تغییر آب و هوا بر جریان کمینه حوضه کرخه، به‌­عنوان یکی از مهمترین حوضه­‌های کشور از لحاظ آورد آبی و کشاورزی، پرداخته شده است. برای این­ منظور، از مدل ریز­مقیاس‌­نمایی دینامیکی PRECIS برای برآورد بارش و دما در دوره 2070 تا 2100 و تحت دو سناریوی A2 و B2 استفاده شده است. برای برآورد دبی روزانه در سال‌های آتی نیز از مدل هیدرولوژیکی SWAT (که یک مدل جامع و پیوسته در مقیاس حوضه‌­ای می­‌باشد) استفاده شده است. بدین­ صورت که مقادیر بارش و دمای خروجی مدل PRECIS تحت سناریو­های مختلف به­ مدل وارد و مقدار دبی روزانه برای زیرحوضه­‌ها برآورد شد. سپس، شاخص­‌های جریان کمینه (سه شاخص Q­­75 ،Q90 و Q95) از منحنی­های تداوم و سری جریان‌های کمینه 10 و 30 روزه در هر یک از زیرحوضه­ها محاسبه شد. بررسی شاخص‌های جریان کمینه طی دوره آینده نشان می­دهد که تحت سناریوی A2، جریان کمینه حدود 70 درصد افزایش خواهد داشت و این افزایش دبی کمینه در قسمت­‌های شمالی حوضه بیشتر است. این در حالی است که تحت سناریوی B2، شاخص‌­ها نشان از کاهش 50 درصدی جریان کمینه در افق 2080 دارند. اما توزیع مکانی جریان کمینه نسبت به دوره پایه تغییری نخواهد داشت. لذا، مناطق مرکزی و تا حدودی شمالی حوضه تحت این سناریو، خشکسالی­‌های شدیدی را تجربه خواهد کرد. از این‌رو، با توجه به اثرات متفاوت تغییر اقلیم بر جریان کمینه تحت سناریوهای مختلف، در طرح‌­های مدیریتی باید عدم قطعیت سناریو­ها و همچنین، وضعیت اقتصادی و اجتماعی منطقه در آینده مد نظر قرار گیرد.

کلیدواژه‌ها

عنوان مقاله [English]

Assessment of climate change impacts on low flows in Karkheh River Basin in 2070 to 2100

نویسنده [English]

  • Sima Rahimi Bondarabadi

Assistant professor of soil conservation and watershed management institute

چکیده [English]

Increasing the greenhouse gases not only has impacts on the weather parameters, but also, has impact on water resources, agriculture, environment, health and economy. Climate change has significant effects on water resources by changing the hydrological cycle. There are several simulation methods for investigating the effects of climate change on different systems in the future, like climate models. The AOGCM model is able to simulate global climate in an area of some ten dousant km2, but, while they are not suitable for regional scale. For this reason, downscaling methods such as dynamic methods are used. These methods are based on high resolution and analysis of climate models. In this research, the impact of climate change was investigated on the low flow of Karkheh Basin as one the most important basins due to its water product and agricultural point of view. For this purpose, the PRECIS which is exponential dynamics and downscaling model, was used to estimate the temperature and precipitation in the period of 2070 to 2100 under A2 and B2 scenarios. The SWAT model, a comprehensive and continuous hydrological model was also used to estimate the flow discharge for the watershed. After calibration and validation of the SWAT model, the amount of rainfall and temperature used as input for PRECIS model under different climate scenarios and finally the daily flow rate was estimated for sub-basins. Then the indices of low flow rates (Q75, Q90 and Q95) and low flow series frequency analysis of 10 and 30 days were assessed. Results showed that rainfall and flow rate have negative and temperature have positive trend. In general, the results of PRECIS model indicated that this model has a good estimate of temperature and precipitation in the region, but, it is not strong for rainfall in autumn and spring, due to the local nature of the precipitation. The climate change assessment under scenario A2, indicated the rise of low flow rate by 70 percent, and this increase of low flow was more in the northern parts of basin, while under the scenario B2 the low flow rate droped by 50 percent for the period of 2080. But, low flow distribution had no change compared to base period.Thus, sever droughts would happen in the central and some northern parts of basin. It can be concluded that under different scenarios, climate change has different impact on the low flow rate. Therefore, due to the different impacts of climate change on low flow rate under different scenarios, uncertainties of scenarios as well as regional economic and social status should be considered in the management plans.

کلیدواژه‌ها [English]

  • AOGCM model
  • Climate change
  • Climate scenarios
  • Downscaling
  • PRECIS model
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