Competition for water on Maui Island, Hawaii, increased drastically over the last fifteen to twenty years, due to a high population and increased economic growth, coupled with declining precipitation and environmental concerns to maintain and protect aquatic habitats. Future projections indicate that demand for water on Maui could exceed supply by 2020. Irrigated agriculture, in particular, sugarcane production plays a major role in the island’s economy, in terms of jobs and incomes. However, irrigation water supply and its efficient management have recently become the major constraints to sugar cane productivity and profitability. Given the fierce competition for the scarce water resources, and persistent economic and political pressure for all stakeholders to maintain water consumption within the stipulated legal limits, the continued production of sugarcane will depend on maximizing efficiencies of water use throughout the whole water supply, delivery and use chain. Currently, the critical concern is the lack of proper water management practices in real-time, resulting in irrigation water either being wasted or sometimes not available when most needed. Our proposed intervention involves the use of the biophysical model ALMANAC as an irrigation water application decision aid tool to optimize water use efficiency at the field level. ALMANAC model calibration for sugarcane was conducted using data extracted from the literature, the Auscane model, and expert judgment. Model adjustments and validation were carried out using actual field data from the Hawaii Commercial & Sugar Company (HC&S) sugarcane plantation. Our preliminary  evaluation of irrigation management scenarios for various fields, weather, soils and tillage cropping practices highlighted management systems that maximize water use efficiency, enhance cane yields, and also minimize environmental impacts on soil carbon storage, sediment and nutrient losses.