بررسی اثرهای تغییرات اقلیم آتی در تبخیر و تعرق واقعی و آب موجود در خاک در حوضۀ آبخیز تالار استان مازندران

به منظور بررسی تاثیر تغییرات اقلیم آتی در تبخیر و تعرق واقعی و آب موجود در خاک در محدوده حوضه تالار واقع در بخش مرکزی استان مازندران، سال آبی 20032004 تا 20062007 به مدت چهار سال برای واسنجی و سال آبی 20082009 تا 20092010 به مدت دو سال برای اعتبارسنجی مدل swat درنظر گرفته شد. بدین منظور، از مدل 5 larswg، که یکی از مشهورترین مدل‏‏‏های مولد داده‏‏های تصادفی وضع هواست، برای تولید سری سناریو‏های مختلف مربوط به ipcc (کمیسیون بین‏الدول تغییر اقلیم مربوط به سازمان ملل متحد) جهت پیش‏بینی دما و بارش آتی استفاده شد. پس از تغییر دما و بارش روزانه برای ایستگاه‏‏‏‏های یادشده، این مقادیر تغییریافته به مدل swat وارد و مدل یک بار دیگر اجرا شد. بر طبق یافته‏‏های این پژوهش، میانگین روزانه (به سال) تبخیر و تعرق در همه دوره‏‏های واسنجی و اعتبارسنجی دارای افزایشی کلی در همه این دوره‏هاست و تبخیر و تعرق در بیشتر ماه‏های آتی بیش از وضعیت امروزی خواهد شد. در مورد آب موجود در خاک نیز، بررسی‏‏ها نشان‏دهنده روند نامنظم در مقدار کاهش و افزایش آب خاک بوده است.

Future Impacts of Climate Change on Actual Evapotranspiration and Soil Water in the Talar Watershed in Mazandran Province

Introduction  Climate change is recognized as a major environmental problem by a majority of the international scientific community. According to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (IPCC, 2007), “global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now it exceeded preindustrial values”. This report further suggests that most of the observed increase in global average temperatures since the midtwentieth century is very likely resulted from rising anthropogenic greenhouse gas concentrations and that, if not controlled, climate effects such as rising sea level, disruption to weather patterns, and ocean acidification pose serious harms to human health, water supplies, agricultural systems, economic performance, and global security. Such projections have triggered calls for prompt and coordinated action to reduce greenhouse gas emissions and adapt to changes in the climate system. Paying attention to climate change event affecting all sections of hydrologic cycle, the goal of this research is to study these phenomena on actual evapotranspiration and soil humidity that play important role in this cycle, with available water for plant, decrease or increase in annual runoff. This can affect all sections of the environmental factors. Materials and methods  Watershed models are essential for studying hydrologic processes and their responses to both natural and anthropogenic factors, but due to model limitations in representation of complex natural processes and conditions, these models usually must be calibrated prior to application to closely matching with SWAT (Soil and Water Assessment Tool). This is a comprehensive and semidistributed river basin model that requires a large number of input parameters, which complicates model parameterization and calibration. Several calibration techniques have been developed for SWAT, including manual calibration procedures and automated procedures using the shuffled complex evolution method and other common methods. In SWAT, a basin is delineated into subbasins, which are then further subdivided into Hydrologic Response Units (HRUs). HRUs consist of homogeneous land use and soil type (also, management characteristics) and based on two options in SWAT, they may either represent different parts of the subbasin area or a dominant land use or soil type (also, management characteristics). With this semidistributed (subbasins) setup, SWAT is attractive for its computational efficiency as it offers some compromise between the constraints imposed by other model types such as lumped, conceptual or fully distributed, and physically based models. For this goals in the boundary of Talar watersheds of Mazandaran province, we selected 8 stations for precipitation, 5 for temperature and discharge, with ShirgahTalar station in output. After preparing maps and necessary weather data, we conducted output of SWAT model for this watershed. In this research, we used water year of 20032004 until 20062007 by a duration of 4 years for calibration and water year of 20082009 by duration of 2 years for validation. For calibration and validation of this model, we also used SWATCUP package software and SUFI2 program.  Results and discussionThe entire Talar watershed is divided into 219 Hydrologic Response Unite in 23 subwatersheds. For assessment of SWAT model from climate change on actual evapotranspiration and available soil water, the SWAT model, further run for this area with new condition. In this stage with definition of HRU for the model, only variated precipitation and temperature are entered into the model to study the influence of these effects on assessment factors in output of the model. To do so, we used variable precipitation and temperature, forecasted by LARSWG model as one of the important model output for random data of weather condition. After change of daily temperature and precipitation for these stations, variation values enter into SWAT model for second run.ConclusionIt can be concluded that the mean daily evapotranspiration (to year) in the time of calibration and validation, is increased for all duration and higher evaporation in majority of future   month. This can be compared with present time that is high index evaporation in May, June, July and August. Study about available water shows unregularly process in decrease or increase of this factor and at least available water in May, June, July and August in the future time that affected hydrologic regularity of the watershed. This can provide water for plant in any month where water is necessary as another environmental factor of area.