Optimal management of water resources in agriculture, particularly under water scarcity, is a major challenge in agricultural planning. This study aimed to determine the optimal cropping pattern and investigate the effects of climatic conditions and different water supply levels on profit and water productivity using a nonlinear programming model in the Dasht-e Naz irrigation unit of the Tajan Irrigation and Drainage Network, Mazandaran Province, Iran. Three climatic scenarios, including dry year (2016–2017), normal year (2009–2010), and wet year (2018–2019), and four water supply levels of 100%, 80%, 60%, and 40% were considered. The objective function was to maximize net profit, while constraints related to water resources, land availability, and nonlinear crop yield–water relationships were incorporated into the model. The results showed that reducing water supply from 100% to 40% in the dry-year scenario decreased the cultivated areas of rice and maize by 27.2% and 26.5%, respectively, while the cultivated areas of wheat, rapeseed, and soybean increased. Crop yields also decreased with reduced water availability; rice yield decreased by 36.6% under normal-year conditions, while wheat and rapeseed yields decreased by approximately 14%. The highest net profit, 954.1 billion rials, was obtained under the wet-year scenario with full water supply, while the lowest profit, 151.2 billion rials, occurred under the normal-year scenario with 40% water supply. Under the dry-year scenario, net profit decreased from 358.4 to 241.6 billion rials, whereas economic water productivity increased from 32.1 to 51.5 thousand rials per cubic meter. Under normal and wet conditions, this indicator increased from 20.2 to 31.8 and from 85.7 to 141.8 thousand rials per cubic meter, respectively. Overall, the results indicated that although reduced water supply decreases crop yields and total profit, adjusting the cropping pattern and allocating water to crops with higher economic returns can improve economic water productivit