Assessment of desertification intensity based on water index using MEDALUS methodology

Sistan plain located in east of Iran which is a very dry territory and also impressed by desert situation. In this area desertification phenomenon makes a transient basis which is not suitable for socio-economic activities specially for agriculture and irrigation. To evaluate the desertification rate regarding to water index in Zabol area, we choose MEDALUS model beyond the others. High precision and reduction of the expert`s mistakes are the two important preferences of this model which is caused by particular weighing of layers and usage of geographic information system (GIS) for over laying of indices` maps. Another important characteristics of this model is its high adaptation of indices and factors with local situation without using a separate method. In this area after choosing the appropriate factors for water index, the maps overlaid by the usage of geometric mean. Regarding determination and desertification of indices in this research two different methods have been used; namely MEDALUS model and modified MEDALUS model in accordance with conditions of Iran. In this region indices and sub indices of water index were chosen in evaluated including indices such as climate, quantity factors, irrigation methods and efficiency as well as wind directions, precipitation, Transou index, duration of drought, amount of sub surface water, shortage of human required water resources, system of surface water collection, type of irrigation system and transition efficiency. Due to the final desertification map, the class of critical (C2 and C3) or very high cover the most parts of this area.