Modeling Water Demands of Irrigation Projects

A simulation model for assessing the water demands of large irrigation areas is developed and applied to the mid‐Canterbury region of New Zealand. Observations from historical water use patterns provide a basis for demand modeling using simplified irrigation watering strategies, highlighting climatic time variability as the single most important influencing factor. Per unit area irrigation demands are first estimated for each identified unique combination of soil, crop type and irrigation strategy using daily soil moisture balance simulation over a number of seasons of recorded climate data. These are then combined using crop areas and efficiency weights to give time patterns of areallyaggregated water demand. The model is checked against field trial data, calibrated against water use in an existing irrigation scheme, and applied to demand estimation for a large proposed future project.