Abstract
Introduction: The destructive phenomenon of desertification is one of the serious ecological crises with widespread and long-term natural and human impacts. Therefore, implementation measures in this field should be based on understanding the current state of desertification and its severity. Considering the practical importance of desertification risk zoning maps, despite the development of quantitative techniques and methods in recent years, efforts are still being made to provide methods with less error and higher reliability. The application of gray logic in solving multi-criteria decision-making problems in uncertain conditions has three characteristics: greater speed and accuracy in achieving results, and ease of use compared to previous models. Therefore, this research aimed to zone desertification risk using gray theory and combining it with the weighted sum multi-criteria decision-making method, and was conducted on a case-by-case basis in the Yazd-Khazarabad plain during the years 2023 to 2024.
Materials and Methods: In this method, after determining the members of the decision-making team consisting of experts familiar with the study area, effective indices were determined and evaluated using the Gray Delphi method. In order to select these indices, three main axes of relationship with the desertification phenomenon, ease of access, and ease of updating were considered within the framework of two factors: cost and time. Then, in order to provide a suitable framework for preparing a zoning map of vulnerability caused by the desertification process, work units were separated using the geomorphological method. Next, a combined analysis process was performed on the data and finally a Harmonic Gray Decision Matrix was obtained. Within the framework of this matrix and by combining the weighted sum decision-making method and gray theory, the indices were ranked and zoned in the ArcGIS environment.
Results: The studies showed that the Mountain Agricultural Grounds unit (MAG) with a quantitative value of 552.73 and the Plain Agricultural Grounds unit (PAG) with a quantitative value of 529.06 were respectively placed in the very severe or VII class, which has the highest desertification potential and covers 7335.76 hectares (9.35 percent) of the entire study area. Desertification with relatively moderate intensity (29.82%) has the largest share in the study area, which includes Bare Mountain Grounds (BMG), Bare Pediment Plant Cover (BPPC), and Bare Clay Grounds (BCG). Meanwhile, the quantitative value of desertification for the entire region from the sum of the factors was 395.86 (severe class or VI).
Discussion: The study demonstrated the efficiency and ease of application of gray logic in assessing desertification severity. The results of this research provide the possibility of planning to minimize desertification as a result of development projects and can create conditions that, considering the priorities and vulnerability zoning of the study area, enable a balance between development projects and the environment. In order to apply this model to other regions, the factors affecting desertification should be considered as indices of vulnerability locally, and the way each factor affects the erosion process should be emphasized. At the same time, due to the existence of uncertain and different input parameters and the presence of some inaccuracy in the obtained results, applying sensitivity analysis to changes in input parameters is a serious need and should be considered in future studies.