Sustainable water resource management in Iran is vital. Population growth, agricultural development, and climate change have increased competition over limited resources, and a lack of integrated allocation has led to reduced environmental water rights and declining groundwater levels. The distinguishing feature of this research lies not merely in the simultaneous application of two models, MIKE HYDRO Basin and WEAP, but in the concurrent simulation of three conflicting demands from the Boostan reservoir and the analysis of zero-sum competition between sectors under two contrasting prioritization scenarios, considering the different allocation algorithms in the two models. Two management scenarios, including equal priority and prioritization of water rights, fisheries, and agriculture, were defined and simulated over a 41-year period. For validation, allocation results, unmet demands, and reservoir performance indicators (reliability, vulnerability, and resiliency) were analyzed and compared in both models. In the prioritization scenario, water rights provision increased by 3.38 million cubic meters (from 29.15 to 32.53), while fisheries and agriculture provision decreased by 0.76 and 3.32 MCM, respectively. Total provision in the first scenario was 49.29 (66%) and in the second scenario was 48.59 (65%) MCM. The second scenario improved operational stability by increasing storage volume and level, but it increased evaporation from 1.74 to 2.16 million cubic meters. Comparison of the models confirmed high convergence of results (64-66 percent) and strong correlation between storage volume and evaporation (0.92 and 0.90). The input data for this research were extracted from real regional data and were sufficient for model execution. Both models are efficient tools for decision-making support in reservoir management with limited resources. To reduce negative consequences on agriculture, improving irrigation efficiency and demand management, as well as emphasizing the necessity of compensatory approaches alongside allocation policies, are recommended. The results of this research are generalizable to regions with similar climates.