Evaluation of Optimal Cropping Pattern in Tajan Watershed with Systematic Modeling

Since in the optimal allocation of water resources, the maximization of income, is the main purpose of modeling, researches in this case is just limited to approaches rooted in linear and structures in mental model or causes the inequitable resources allocation. Also, evaluation of these researches showed that there is low knowledge about long term dynamics behavior in river watershed. In this regard, in this study, evaluation of optimal cropping pattern based on water resources and demand in Tajan watershed by VENSIM in 1962- 2012 in monthly times step was carried out which domestic, industrial, environmental and agricultural demand were taken into account. This optimal cropping pattern could be the basis for water productivity in Tajan watershed. The calibration results showed not only outflow of dams is related to demands, but also dams coefficient is independent from agricultural demands coefficient. Also the results showed that large amount of domestic, industrial and environmental demand in this region is supplied and dams in Tajan watershed is enough for suppling. But there is significant deficit in agricultural part that regarding to low volume of groundwater in this region, changing crop pattern s inevitable. O the other hand, evaluation of optimal crop pattern is showed that orchards with maximum income per cost in the all region, is dedicated the most cultivated land area and after that citrus have second priority.