بررسي و مقايسه روند بيابان زايي در مناطق خشك و نيمه خشكبا تاكيد بر معيار اقليم (مطالعه موردي: دشت عباس و دشت دهلران، استان ايلام)

The study and Comparison of desertification process on the basis of climate Criterion Case Study: Abbas and Dehloran Plains, Ilam

در حال حاضر بيابان ­زايي به ‌عنوان يك معضل گريبان­گير بسياري از كشورهاي جهان از جمله كشورهاي در حال توسعه است. اين معضل مشتمل بر فرآيندهايي است كه هم زائيده عوامل طبيعي بوده و هم به عملكرد نادرست انسان برمي­گردد. هدف از اين پژوهش مقايسه بيابان زايي و خشكسالي دشت عباس و دشت دهلران به ترتيب با مساحت 34104 و54252 هكتار مي باشد.در اين مطالعه با استفاده از مدل ايراني IMDPA شدت بيابان‌زايي دشت عباس و دشت دهلران در دوره زماني 88-1384و 93-1389 مورد ارزيابي قرار گرفت. به همين منظور معيار اقليم به عنوان موثرترين معيار ارزيابي بيابان‌زايي در نظر گرفته شد. براي معيار اقليم سه شاخص بارش سالانه، شاخص خشكسالي SPI و استمرا خشكسالي در نظر گرفته شد. بعد از آماده سازي داده‌ها با استفاده از جدول امتيازدهي مدل IMDPA هريك از شاخص ها بصورت لايه هاي اطلاعاتي وارد نرم افزار Arc GIS 9.3 شد. در نهايت با استفاده از ميانگين هندسي نقشه هاي تهيه شده دو دوره زماني با هم ادغام شده و با قرار دادن لايه هاي امتياز دهي شده سه شاخص مذكور نقشه نهايي مدل IMDPA از اقليم دشت عباس و دشت دهلران تهيه گرديد. نتايج تحقيق نشان داد كه شاخص SPI به عنوان موثرترين شاخص،در دشت عباس در دو دوره به ترتيب با ميانگين وزني 04/3 و 5/3 در طبقه شديد با زير كلاس 2 و 3 قرار دارد. در مقابل در دشت دهلران نيز شاخص SPI در دوره اول و دوم با ميانگين وزني 93/1 و 25/2 در طبقات متوسط زير كلاس 1 و 2 و 3 و شديد زير كلاس 1 قرار گرفته است. مي توان نتيجه گرفت كه شدت بيابان زايي در دشت عباس در مقايسه با دشت دهلران از نظر اقليم در شرايط نامطلوبيقرار دارد. بطوري كه وقوع بيابان‌زايي با شدت بيشتر در دهه‌هاي آتي دور از انتظار نخواهد بود

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.