Desertification-Intensity Zoning through Fuzzy-Logic Approach: A Case Study of Deyhook-Tabas, Iran

Destructive phenomenon of desertification is one of the serious ecological crises at the present time. In order to improve efficiency of combating desertification projects and inhibiting destruction of natural resources and our asset, it sounds considerably meaningful to reach a systematic and comprehensive method that can use different criteria and indicators to provide optimal solutions. Traditional models of desertification assessment are based on defined thresholds and limits and in the real nature of ecosystems, there are no boundaries and contractors. So, there is always a level of uncertainty in the phenomena such as desertification mapping.
THEORETICAL FRAMEWORK: Land degradation assessment strategies are based on experts’ opinions, and usually the evaluation methods based on multi-criterion decision-making models are not concerned in Iran. Until now, clear and uniform procedures for the classification of desertification have not been provided based on desertification processes. In this regard, the identification and evaluation processes, and the identification of current state of desertification intensity are generally among the basic requirements of desert areas. In the present paper, the fuzzy approach, as one of the effective ways to assess desertification, has been used. For this purpose, it should be noted that in fuzzy methods, the thresholds of each class can be reviewed in different management scenarios.
Some indices of climate, soil and water criteria were selected to be considered for each condition of the region. The samples were collected in homogeneous units in Deyhook basin. The next step was converting layers to fuzzy layers by linear functions of fuzzy membership. Final desertification intensity was calculated based on fuzzy overlaying via gamma operators of the selected criteria and their indices on a scale of zero to one. The numerical value was reclassified into 4 levels including low, medium, severe and very severe, and the desertification intensity map was drawn using GIS in the studied period. For the vegetation and precipitation indices, the decreasing fuzzy function, and for the others, the increasing fuzzy function were used.
According to the results, among the studied areas, approximately 14.5% of the area was very severely degraded and 3.5 percent was in the intensity of severe class. Most of the basin was allocated to the moderate intensity of desertification class and if the current trends continued increasing desertification, it would be under more severe desertification risk. It is important that severely and very severely degraded areas have the largest population centers. In fact, these areas are located mainly in rural areas, and it seems that the population pressure makes an improper use of surface and underground water resources. According to the results, 81 percent of the basin, sodium adsorption ratio is higher than 32. Aside from sodium ion toxicity effects on plants, along with increasing SAR, available water for plants is reduced subsequently. According to the results of the current study, 91 percent of the basin Deyhook, EC soil is more than 17 dS m. High salt levels lead to plant growth reduction and biomass loss.
CONCLUSIONS AND SUGGESTIONS: The strength of fuzzy method is that the indices map and the final map of desertification have a dynamic and continuous nature, and therefore, the intensity class boundaries can be changed according to the user requirements in various management and land reclamation scenarios. Given that environmental restrictions in the basin Deyhook are very intense, so changes in the cropping pattern, dependent reduction in livestock pastures, reduction of human dependence on nature and the use of varieties resistant to drought and salinity are among the cases that can be offered to slow the desertification Deyhook basin. It is recommended in the mentioned basin that halophytes species and tolerant species such as Salsola and Atriplex be utilized in agricultural and rangeland management plans.