Investigation of desertification status using IMDPA model considering wind and water criteria (case study: Bahabad region, Yazd province)



Extended abstract
1- Introduction
The reduction of biomass in arid, semi- arid and semi- humid ecosystems is called desertification. In recent years, processes of desertification have created many unrepairable damages. Desertification in developing countries and in countries with the high potential of decortications is more severe. Then, control of this phenomenon, spatially in these countries is more useful. To present the strategies and suitable methods for management in this background, understanding of effective parameters in desertification is very important and virtual that it should be investigated. Many researches for investigating the condition of desertification have been done by some researchers in the world such as Harasheh et al (2000), Ladisa et al (2002), Lira (2004), Monia Santini et al (2010), Faiz nia et al (2000), Abrisham (2004), Khosravi (2004), Fallah mehne (2004), Sepehr (2005), Ahmadi (2006), Zehtabian et al (2006), Chaman pira et al (2006), Abdi (2007), Tabatabaei (2010).

The general aim of this research is to investigate the condition of desertification in the study area by measuring the soil erosivity and determining their effective factors and critical areas for controlling the desertification. For doing that the IMDPA model has been used as this model is the result of integrated plan of indices and criterion of desertification in Iran. This model is the first one that has presented for quantification of effective indices of desertification in biomes of Iran.
In this research, for investigating the condition of desertification and presenting its map the IMDPA model has been used and indices of water and wind erosion have been investigated. Land desertification was studied in map unit and under arid climatic condition. For criteria of water erosion, four indices (water erosion density and type, land use, vegetation density) were investigated and their data layers were created in GIS system environment. After that by laying each pair of data layers, the final score of water erosion criteria was obtained in each unit by equation 1.
I= equation (1)

1≥ i ≥4
I: the final score of index of desertification potential based on water erosion criteria in each unit.
Ii: the score of each index in each unit.
For wind erosion criteria, their indices (appearance of erosion, density of non- alive cover and the numbers of dusty days) were measured by laying these digital layers, the final score of wind erosion criteria in each unit was obtained.
I= equation (2)
1≥ i ≥3

I: final score of index of desertification potential based on wind erosion criteria in each unit
Ii: the score of each index in each unit.
Finally, the intensity map of desertification based on criteria of wind and water erosion was provided separately.

The obtained results show that surface cover has important role in desertification phenomenon from viewpoint of water erosion (vegetation index) and also from viewpoint of wind erosion criteria (density of non alive and vegetation). Some parts of this problem is due to the climatic condition of study area such as arid climate, less rainfall, high evapotranspiration, have been created sever condition. This point, following the intensitive drought in recent years, has been made the reduction of quantity and quality of vegetation.
Moreover, railway, and other communicational roads (like Bafgh- chadormaloo) has been effective in degradation of vegetation.
With respect to the obtained results, the important factors in erosion (wind and water) and desertification phenomena can be introduced as follows:
• Intensive and erosive winds that leads to the moisture reduction, degradation of vegetation and finally detachment and transport of windy sediments.
• Daring water erosion in sensitive formations in mountains of study area, fine sediments hare been scattered on the surface and finally these sediments can be moved by wind erosion. Moreover, inappropriate activities by some organizations (such as embankment dams) have been lead to severity of wind erosion.
• Dominant of dry climate, less precipitation and high evapotranspiration, has been created hard conditions in the study area. This point following the sever droughts in recent years have increased the wind erosion in study area.
• Release of agricultural lands, especially near the Shour river of Bahabad.
• Constructions of many roads have also been created water and wind erosion.
• Digging the deep wells for agricultural and industrial activities
• Transgression to riversides and water ways and non scientific planting (especially around the Shour River in Bahabad).
Overall, it can be stated that although the natural factors have been affected in desertification, but human parameters have also created desertification directly (land degradation) and indirectly (as a factor on intensification of degradation of natural factors). This point is also accordance with the results of sepehr (2005) in regarding to the effects of desertification in south of Fars province and Chamanpira (2006) for desertification in kouh- Dasht watershed.

IMDPA model is integrated and complete method that has been calibrated with Iran conditions, then this method has less error. Moreover, existing the sufficient numbers of indices (coinciding with the area condition) has been made to obtain the good estimation from desertification condition. In the other hand, to access the results it is essential to investigate the other criterion of IMDPA model such as climate, geology, geomorphology, soil, vegetation, agriculture, water, social- economical problems and technology of city development.
Finally and witch respect to the results of this research that surface cover is important factor in intensification of wind and water erosion, than it is essential to change the sight of people and users to natural resources.
Therefore, considering the environmental problems and land logistic rules for each project in the study area is essential. Moreover, instruction the local communities and increasing the level of information and knowledge of decision makers and users can improved the sustainable development and lead to the control of desertification.