Optimal fallow area and location for multifunctional benefits of a paddy field during drought periods

Paddy fields not only serve to produce food but also have a variety of important ecological functions. Apart from the internal benefit (i.e., crop production), there are external benefits (i.e., reduction of greenhouse gases, oxygen generation, reduction of biological oxygen demand, flood mitigation, and other functions that are difficult to quantify). In the present study, the optimal fallow locations and areas were determined for evaluating the multifunctional benefits of paddy fields during drought periods, by using an optimization model for fallow fields under different exceedance probabilities of river inflows. For each time step, the appropriate probability distributions for river inflows to the Chi-Chi Weir (range 50–90 %) for generating system inflows were obtained. The optimization model for fallow fields was solved using Lingo. It was observed that the external benefits of paddy fields accounted for 76 % of total benefits, with the production benefit accounting for the remainder. The total benefits decreased as the exceedance probability of river discharges increased. Our findings indicate that fallow areas increase as irrigation areas shift downstream.