Modelling future irrigation demand at a statewide level: lessons from Florida USA

Water resource managers must consider supply constraints, planning horizons, climatic trends and competing uses to understand where water will be needed most in the future. Agricultural water demand is an important consideration, with Australian agriculture consuming 10,730,000 ML of water in 2014. While models exist to predict water use for individual farms, predicting future agricultural water use in Australia at the state or national level is more challenging. The Balmoral Group developed a model to predict agricultural water demand for the entire state of Florida, USA as part of the Florida Statewide Agricultural Irrigation Demand (FSAID) project. Balmoral prepared a Statewide, property-level geodatabase of irrigated agricultural lands using aerial imagery, permit information, and computation of the Normalized Difference Vegetation Index. Water applied for irrigation was estimated using an econometric model based on the water use of 3,200 farms over three years, and the demand for irrigation water for a range of biophysical and economic factors relevant to each farm. The coefficients in the model were used to populate water use for the remaining farms across the State using spatially specific, farm-level data. Special situation water-uses such as frost protection, fertigation and crop establishment water for annuals were evaluated before preparing agricultural acreage projections and associated water requirements. Future projections of irrigated area and water use were estimated using auto-regressive forecasts of landuse change and net crop prices. A similar approach could be applied here in Australia to help plan for and manage the future demand for agricultural water.