The main purpose of this study is to identify the optimum allocation of limited amount of land and irrigation water across a number of alternative farm enterprises, maximising the whole-farm profitability by considering present relative prices, changes in river water availability, irrigation system efficiency and a highly variable climate. It was developed an optimisation model by using linear programming language to maximise the whole-farm profit of farm located in Wee Waa (NSW, Australia), for three different scenarios (dry, average and wet years) over two seasons. The whole-farm profit is highly sensitive to climate variability and also to prices and yields variability, especially in relation to cotton.