Potential assessment of suitable lands for walnut cultivation in Tehran province using fuzzy AHP method

As a highly productive product, walnut plays an important role in the social and economic condition of farmers in various regions across Iran, and there has been a dramatic increase in the area under cultivation of this product in recent years due to its economic return. Walnut trees are highly sensitive to the climate conditions. Therefore, before Cultivation of this product, which requires a relatively high initial investment, it is necessary to take certain measures to identify and assess suitable lands for planting walnut trees. Therefore, this study aims to identify and assess suitable lands for planting walnut in the entire of Tehran province that would result in a desirable production efficiency. For this purpose, this study uses climatic parameters (including temperature, relative humidity, precipitation, and wind speed) from 12 synoptic stations within Tehran Province and 8 stations from adjacent provinces for an 11-year statistical period (from 2004 to 2014), topography, and land use for site selection and zoning of suitable regions for cultivation of Persian walnut. First, raster data layers were generated using all the parameters under study. Then, through a review of literature and expert views on physiological properties and growth requirements of walnut, the desirable and undesirable thresholds for its cultivation were determined. Next, analytic hierarchy process (AHP) and a researcher-made questionnaire were used to calculate the effectiveness and priority of each parameter. Furthermore, a fuzzy membership function was used to normalize the data layers. Finally, the final zoning map was prepared and extracted using fuzzy overlay tools in ArcGIS. According to this map, an area of 243882.9562 hectares, equal to 17.82% of the entire area of Tehran Province proved very suitable for cultivation of Persian walnut. Moreover, the findings indicate that the three parameters of temperature, relative humidity, and aspect have a special significance and effect on the growth of walnut trees.