ارزیابی شدت بیابان‌زایی با تاکید بر معیار آب زیرزمینی با استفاده از مدل imdpa (مطالعه موردی: دشت مهران، استان ایلام)

بیابان‌زایی کاهش توان اکولوژیکی و زیستی زمین است که به دو صورت طبیعی و مصنوعی رخ می‌دهد. این پدیده از معضلات مهم کشورها در چارچوب برنامه مدیریتی توسعه پایدار است که خود نتیجه برآیند مجموعه‌ای از عوامل مختلف محیطی، انسانی و اقلیمی است. در این رابطه از عوامل مهم و تاثیرگذار، عنصر آب است که به‌عنوان منشا حیات و تضمین‌کننده بقای اکوسیستم‌های پایا است. با توجه به اهمیت آب در اقلیم خشک و نیمه‌خشک نسبت به اقلیم‌های دیگر، می‌بایست تمهیداتی برای مدیریت صحیح آب به‌عمل آورد تا از ایجاد شرایط بحرانی در این مناطق جلوگیری کرد. هدف از این مطالعه بررسی وضعیت معیار آب به­منظور ارزیابی بیابان‌زایی است. با توجه به اثرات فراوانی که شاخص‌های آب در گسترش عرصه‌های بیابانی دارند، در این پژوهش سعی شده است با استفاده از شاخص‌های کمی و کیفی آب‌های زیرزمینی همچون هدایت الکتریکی (ec)، نسبت جذب سدیم (sar)، کلر (cl)، افت آب زیرزمینی و سیستم‌های آبیاری به بررسی و تعیین کلاس شدت بیابان‌زایی در دشت مهران با استفاده از مدل imdpa پرداخته شود. نتایج به‌دست آمده نشان داد که در این منطقه شاخص‌های افت آب زیرزمینی و سیستم آبیاری به‌ترتیب با متوسط ارزش عددی 3.11 و 1.75 بیشترین تاثیر را در روند بیابان‌زایی منطقه دارند. با توجه به نقشه وضعیت معیار آب زیرزمینی در تخریب منابع منطقه می‌توان دریافت که 32 درصد از کل منطقه در کلاس کم، 48 درصد در کلاس متوسط و 20 درصد از کل منطقه در کلاس شدید بیابان‌زایی قرار گرفته‌اند. به‌طور کلی، ضرورت دارد که مدیریت منابع آب برای جلوگیری از گسترش بیابان‌زایی در اولویت سازمان‌های اجرایی قرار گیرد.

evaluating desertification intensity with emphasis on groundwater criteria using imdpa model (case study: mehran plain in ilam province)

desertification is defined as the reduction of the ecological and biological potential of the earth, which occurs both naturally and artificially. this phenomenon is one of the important problems of countries for sustainable development management programs, which is the result of a combination of various environmental, human and climatic factors. water is recognized as an important and influential factor that is the main source of life and also guarantees the survival of sustainable ecosystems. since water is more important in arid and semi-arid climates than in other climates, measures should be taken to properly manage water in order to prevent critical conditions in these areas. the purpose of this study is to investigate the status of water criteria to assess desertification. due to the many effects that water indices have on the development of desert areas, in our study, we used quantitative and qualitative indices of groundwater such as electrical conductivity (ec), sodium absorption ratio (sar), color (cl), falling groundwater level and irrigation systems to study and determine the class of desertification intensity in mehran plain. the imdpa model was applied to evaluate the desertification situation. the results showed that the indices of decline and irrigation systems with average values of 3.11 and 1.75, respectively, have the greatest impact on the desertification process in the region. according to the groundwater status map in the destruction of resources in the study area, it can be concluded that 32% of the total area is in the low class, 48% in the middle class, and 20% of the total area is in the severe desertification class. in general, water resources management should be a priority for executive agencies to prevent desertification.extended abstract1. introductionfor proper management and planning of arid and semi-arid regions, it is necessary to understand the influence of the factors, indicators, and criteria on desertification in areas that are deserted or prone to desertification. the use of poor quality water is one of the factors affecting soil salinity and creating a suitable condition for the development of desert conditions. the purpose of this study is to evaluate the intensity of desertification using the imdpa model with emphasis on groundwater criteria in the mehran plain in ilam province.2. materials and methodsthe study area is located in mehran plain in ilam province in western iran. recharge and drainage of the region are by two rivers of gavi and konjancham. according to the geological situation and the information obtained from the exploration wells and exploitation of mehran plain, the groundwater aquifer is the unconfined aquifer. the average rainfall and temperature of the study area are 270 mm and 21.5°c, respectively. according to the domarten climate, the study is defined as a dry climate according to the de martonne climatic classification (de martonne, 1926). in this study, the imdpa model (iranian model of desertification potential assessment) was used to investigate the intensity of desertification and to present a desertification map in the mehran plain. this method is one of the methods of desertification assessment that was proposed in 2005 by the department of deforestation and natural resources of the university of tehran in collaboration with the forests and rangelands organization (zakerinejad et al., 2012). by using this model, it is possible to study the effective parameters in desertification in order to provide an accurate desertification map according to the conditions of iran (akbari et al., 2020). in this study, to investigate and prepare a criterion map of groundwater degradation from imdpa model indicators including electrical conductivity (ec), sodium absorption ratio (sar), color (cl), falling groundwater level and irrigation systems of the irrigation system were used. the inverse distance weighting (idw) method was used to prepare raster maps of different groundwater indices. finally, after preparing maps related to each indicator and combining their layers in the gis environment, the groundwater criterion was obtained, which was applied in the final assessment of the desertification situation in the region.3. resultsthe results showed that in the study area, the groundwater criterion is in three classes of low, medium and severe desertification. according to the groundwater condition map in the degradation of regional resources, about 32% of the total area is in the low class of water degradation which is located in the northwest and southeast of the study area. moreover, approximately 48% of the total area is in the middle class, which is located in the northern and northeastern parts. about 20% of the total area is also in the severe class, which is mainly concentrated in the southeastern part of the region. these results were obtained from the study of different indicators of groundwater resources. the results of the aquifer decline index in land degradation situation showed that this index was in low, medium, severe and very severe classes. sodium absorption ratio index in low and medium classes as well as irrigation system index is in low and severe land degradation. the electrical conductivity index was in low, medium and severe classes and the chlorine index was in the low class for land degradation.4. discussion and conclusionthe data of the impda model showed that among the measured indices (falling groundwater level, sodium uptake ratio, electrical conductivity, chlorine and irrigation system) in this study, falling groundwater level and irrigation system have higher sensitivity, respectively. they can be more effective in desertification classes. the findings of rafie emam and zehtabian (2004) showed that flooding irrigation and furrow methods are the most important factors in desertification. in fact, traditional irrigation methods cause high water consumption, resulting in declining groundwater aquifers. therefore, it is necessary to adopt appropriate strategies to eliminate the aquifer decline, which has the highest value in terms of land degradation in water criteria. in general, the results showed that water is an important and effective factor in monitoring the intensity of desertification, especially in arid and semi-arid regions. it is suggested that to combat desertification, proper management of water resources should be done to prevent critical conditions in these areas.