بررسی و مقایسه روند بیابان زایی در مناطق خشک و نیمه خشکبا تاکید بر معیار اقلیم(مطالعه موردی: دشت عباس و دشت دهلران، استان ایلام)

در حال حاضر بیابان زایی به‌عنوان یک معضل گریبان گیر بسیاری از کشورهای جهان از جمله کشورهای در حال توسعه است. این معضل مشتمل بر فرآیندهایی است که هم زائیده عوامل طبیعی بوده و هم به عملکرد نادرست انسان برمی گردد. هدف از این پژوهش مقایسه بیابان زایی و خشکسالی دشت عباس و دشت دهلران به ترتیب با مساحت 34104 و54252 هکتار می باشد.در این مطالعه با استفاده از مدل ایرانی imdpa شدت بیابان‌زایی دشت عباس و دشت دهلران در دوره زمانی 88-1384و 93-1389 مورد ارزیابی قرار گرفت. به همین منظور معیار اقلیم به عنوان موثرترین معیار ارزیابی بیابان‌زایی در نظر گرفته شد. برای معیار اقلیم سه شاخص بارش سالانه، شاخص خشکسالی spi و استمرا خشکسالی در نظر گرفته شد. بعد از آماده سازی داده‌ها با استفاده از جدول امتیازدهی مدل imdpa هریک از شاخص ها بصورت لایه های اطلاعاتی وارد نرم افزار arc gis 9.3 شد. در نهایت با استفاده از میانگین هندسی نقشه های تهیه شده دو دوره زمانی  با هم ادغام شده و با قرار دادن لایه های امتیاز دهی شده سه شاخص مذکور نقشه نهایی مدل imdpa از اقلیم دشت عباس و دشت دهلران تهیه گردید. نتایج تحقیق نشان داد که شاخص spi به عنوان موثرترین شاخص،در دشت عباس در دو دوره به ترتیب با میانگین وزنی 04/3 و 5/3 در طبقه شدید با زیر کلاس 2 و 3 قرار دارد. در مقابل در دشت دهلران نیز شاخص spi در دوره اول و دوم با میانگین وزنی 1/93 و 2/25 در طبقات متوسط زیر کلاس 1 و 2 و 3 و شدید زیر کلاس 1 قرار گرفته است. می توان نتیجه گرفت که شدت بیابان زایی در دشت عباس در مقایسه با دشت دهلران از نظر اقلیم در شرایط نامطلوبی قرار دارد. بطوری که وقوع بیابان‌زایی با شدت بیشتر در دهه‌های آتی  دور از انتظار نخواهد بود

the study and comparison of desertification process on the basis of climate criterion (case study: abbas and dehloran plains, ilam)

the study and comparison of desertification process on the basis of climate criterion (case study: abbas and dehloran plains, ilam)soraya yaghoobi, kamran karimi, marzban faramarziabstract: nowdays desertification is a disaster in many countries , especially in developing countries. this problem includes natural factors and improper human activities. according to the expansion of desertification, providing the appropriate management methods will be reduced desertification intensity and its expansions. in this way, knowledge of processes of desertification and factors causing and  the intensifier it and also awareness of intensity and weakness the processes and factors that are important and necessary   that should review and evaluate. recognition criteria and indicators for provide a model to show the process of desertification and for determine one of the  best reason effective factors for prevent the spread of desertification factors is necessary. to knowledge and trend of desertification and separation of  vulnerable  areas versus degradation factors .we should indentifi and evaluat  criteria and indicators affecte  at desertification. therefore in this study of  the iranian model imdpa to assess trends and comparison of desertification in recent years has used.the studied area of  dehloran plain is located in southeast of ilam province (47◦ 02′ 16″ to 47◦ 25′ 07″ e and 32◦ 48′ 33″ to 32◦ 18′ 48″n) with an area of 54252  hectares, with precipitation  average 251.6 mm and abbas plain is located in south of ilam province(47◦ 37′ 55″ to 47◦  50′ 57″ e and  32◦ 17′ 77″ to 32◦ 29′ 25″n) with an area of 34104 hectares with precipitation  average 227.1mm. in this study, in dehloran plain of six stations in this inside and outside the area also in abbas plain of five  stations outside the area  used to measure the amount of rainfall in different seasons of year. in this study, to assessment  and comparison of desertification in two study area of the iranian model imdpa used. in this study, of climate criteria, were used. which according to the imdpa model for this criteria, indexes are considered for evaluation e.t.c: climate criteria: (1) the amount of annual rainfall 2-drought indexe(spi) 3. continuing drought in imdpa model  all measurements  do in this work  units. to this end, first, working unit maps (geomorphologic facies) were created using slope, geology, and land use maps. a map was generated for each index according to assigned weights, such that the qualitative map of the desired criteria were obtained using the geometric mean of indicators. the results earn  of  evaluation  of desertification  showed that  in the period  2005-2009  weight average of climate criteria is same with 1.50 all of the region are in the classe middle sub class 1 and class low sub class3 . in the period  2010-2014  also  weight average of climate criteria is same with 1.88 in classe middle sub classes 2 and 3.  also weight average of climate criteria in abbas plain in the first period is same with 1.92  in the classe middle sub classe2. also in the second period with weight average is same 2.3 in classe middle sub classes 2 and 3. the results showed that spi index, as the most effective indexes, in plain abbas in the first and second periods with the weighted average 3.04and 3.2 in the intense class under class 2 and 3. in front in dehloran plain spi index in the first and second periods with weighted average of 1.93 and 2.25 in the moderate classe and sub-classes 1, 2 and 3 and intense sub-classe 1.in this study, to assess and comparison of desertification dehloran and abbas plains to provide regional model has done. . in this way  of  a criteria, also important and effective indexes belonging to this criteria of desertification used in dehloran and abbas plains . the obtained results of the analysis criteria and indexes indicated that in dehloran and abbas plains in the first period ( 2005-2009) and second period (2010-2014)  between  indexes  the amount of annual rainfall, standard precipitation index (spi) and drought duration evaluated on the areas respectively standard precipitation index (spi),  rainfall and drought duration index the most important factors in exacerbating desertification. can be concluded that the intensity of desertification in abbas plain compared to dehloran plain terms of climate is in more adverse conditions. in general, it can be concluded that desertification would intensify in future decades.keywords: desertification, imdpa, climate, abbas plain, dehloranplain