عنوان مقاله [English]
Land degradation and desertification have emerged as one of the world's most pressing environmental and socio-economic challenges, posing a serious threat to global development. Therefore, it is vital to comprehend the worldwide pattern of this land disaster. Desertification and land degradation are two problems at national, regional, and global scales and fighting them has been a global effort since 1992. More than 75% of Iran's area has arid and semi-arid climate conditions. Therefore, this region has a high sensitivity to land degradation and desertification. In recent decades, natural factors such as climate change and anthropogenic influences have played effective roles in providing proper conditions for land degradation worldwide. Arid ecosystems show different forms of land degradation such as salinization of water and soil resources, wind erosion, vegetation degradation, etc. that contribute to desertification. Early monitoring and identification of land degradation through the application of simple and fast ways to alert people and prevent future threats is one of the key goals of various scientific and political groups worldwide. Due to the important role of identifying sensitive ecosystems to land degradation to reduce its impacts (especially in weak and fragile ecosystems), in this research, in order to identify sensitive ecosystems and determine the type of climate involved in land degradation in Khuzestan province, the statistical rates of land degradation in different climates and ecosystems of the mentioned region were assessed.
Khuzestan province with an area of about 64234 Km2 is located between 47º41ʹ 00ʹ to 50º 31ʹ00ʺ east longitude and 23º 04ʹ 00ʺ to 29º 58ʹ 00 ʺ north latitude in the southwest of Iran on Persian Gulf and Arvand River. This province is the center of Iranian oil extraction industry and Ahvaz city is its capital. This province is part of Persian Gulf coastal plains, hot and dry southern regions, and Gulf vegetation region. The province's average rainfall is estimated to be 150 mm. Although average air humidity in Khuzestan is 50%, the majority of Khuzestan plain is dry and desolate due to minimal rainfall. Rainfall in the province increases from south and southwest to north and northeast. Northeast has the highest rainfall, with an average of 616 to 700 mm, and southwest has the lowest amount, with an average of 125 to 225 mm. Annual average temperature is between 24 and 28 ◦C. Evaporation rate is estimated to be 2000 mm per year. Based on the climatic divisions of Amberje, the province includes extreme hot deserts and hot temperate deserts. In terms of topography, it consists of two mountainous parts in north and northeast and a plain in south. There are 500,000 hectares of forests and 5.2 million hectares of rangelands in Khuzestan province. Rangelands are poor winter rangelands with richer vegetation in mountainous areas. Of overall forests, 10% are of good grade, 30% are scarce, and the remaining is degraded and unusable.
FAO-UNEP and NDVI vegetation indices were utilized in this investigation. Because NDVI vegetation index depicts the state of cover, it can be used to study the current state of land degradation as a result of effective elements in degradation (rainfall, soil, land cover, etc.). For this purpose, MODIS vegetation images recorded in the range of 2011 and 2013 were extracted from USGS site and their geometric positions were corrected. Three images obtained in March, April, and May in the mentioned years, which represented the highest production, were selected. Then, to eliminate changes between 2011 and 2013, an image representing the maximum production in the aforementioned three months was generated and the maximum images were averaged. Then, maps of rainfall, land use, and land unit were combined to determine work units in GIS environment. The current production values of NDVIMAX and potential production (NDVIPOTENTIAL) were replaced in FAO-UNEP equation and by determining their values in each unit of work and with the help of FAO-UNEP equation, risk classification of the current situation of land degradation was performed in five classes. Then, using network method, we investigated the extent of degradation in Khuzestan province climates (very arid, arid, semi-arid, Mediterranean, semi-humid, humid, and very humid) and different ecosystems (desert, rangeland, rainfed, and forest) as determined by Domarten Climate Index (ultra-arid, arid, semi-arid, Mediterranean, semi-humid, humid, and very humid). The samples were random-systematic with a network size of 5×5 km. To explore the extent of difference in degradation in different climates and ecosystems of Khuzestan province, land degradation, climate, and land use maps and Point maps were integrated into GIS, and maps of each climate and ecosystem were generated independently. Finally, the analysis of variance and Duncan test in SPSS software were applied for statistical analysis of different degradations in various climates and ecosystems.
The results of the analysis of variance showed that land degradation in different climates and ecosystems of study area was significant at the level of 1%. Very arid climate (53.75 %) had the highest risk of land degradation, followed by dry climate (32.53%). In semi-arid, Mediterranean, semi-humid, humid, and very humid climates, the prevalence of land degradation was in middle-risk category and in terms of land degradation, there were no significant differences among the mentioned climates. The results also showed that desert ecosystems (81.95%) and rangeland ecosystems (49.20%) were in the categories of severe and very severe land degradation, respectively, and there was no statistically significant difference between forest and rainfed ecosystems in terms of land degradation. Also, the predominance of land degradation in these two ecosystems was related to middle-risk class. In rainfed and forest ecosystems, the percentages of severe and extreme hazard classes were higher than those of no risk and low-risk classes. Finally, it could be said that the reason for more severe land degradation in drier regions of Khuzestan province was related to the conditions of that region because its areas were semi-desert (they have not reached the final level of desert) and did not have the conditions of complete desert areas. Also, given that the rate of land degradation in desert ecosystem was the highest, we were faced with new concepts such as man-made or new deserts. It was hoped that the results of the present study and the application of this method could help managers and relevant officials in identifying ecosystems and climates sensitive to degradation to better plan and manage these areas to prevent further land degradation and desertification.
Current state of land degradation; Climate; Ecosystem; GIS; MODIS images.