Water resource allocation and crop performance simulation in Tajan irrigation and drainage network with coupling of WOFOST and VENSIM models

Integrated water and land resource's strategies requires consideration of physical process in bio-physic model parallel to hydrological, agricultural, social and economic feedbacks in dynamics system. Coupling SD-based models of with physically- based models of environment is therefore a promising method for obtaining the best of both worlds to enable data exchange between different models which could cover the complex behavior caused by the various interactions. Therefore, in this study, in order to water resources allocation and performance estimation of Tajan irrigation and drainage scheme, VENSIM dynamics system model and WOFOST crop growth model were developed using scripting approach and PySD-PCSE coupling model. On this basis, the VENSIM and WOFOST models were first applied and calibrated in 2015, and were returned to Python according to coding instructions and the integration of the two models was performed. The results of the present study showed that the water resources balance was insufficient to supply agricultural demand, and from 155 million cubic meters, only approximately 81 million cubic meters were supplied that the deficiencies for fruits, citrus, rice, grain maize, cereal, oilseed and wheat are 52, 25, 30, 2, 1.2, 0.05, 1 and 1.52 MCM, respectively, which greatly impacts on crop yield. Also, according to the poor potential of water resources in the Tajan scheme, the calculated yield for crops such as corn, wheat and oilseeds is significantly different from the actual yield of crops. On the other hand, since the potential water resources of the Tajan irrigation and drainage scheme are insufficient to provide for agricultural demands, no supplies have been made for pulse in all areas and for oilseeds, wheat, corn and beans in some areas. Also, in order to estimate the best yield function of the coefficient of explanation of the different plotted graphs, the results of this comparison showed that all of these functions are of polynomial type and are consistent with the Dornbus-Kasam relation.