Model Overview

Agricultural Water Demand (Lead: Cynthia Schwartz)

The Agricultural Water Demand sub-model estimates daily water demand for IDUs with agricultural land cover types (hay, grass seed, corn, pasture, wheat, orchards/vineyards/tree farms, clover, fallow, and other crops). For each cover type, the sub-model estimates daily water evapotranspiration as a function of climate, crop type, crop growth stage and available soil water capacity. For annual crops, the sub-model also estimates crop planting and harvest dates. On irrigated fields, the model estimates the demand for water from irrigation as the difference between field capacity and soil moisture.

Irrigation and Crop Decisions (Lead: Bill Jaeger)

The Crop Decision sub-model determines the crop type in IDUs with annual crops. It first calculates the probability of growing each of eight crop categories for the modeled year. The probability functions relate the chance of choosing to grow a particular crop in each IDU to static characteristics, such as agricultural soil capability class and the presence of an irrigation water right, and to variable characteristics such as the price of wheat and April 1 snowpack. The sub-model then sets the crop type for each IDU, with crops with a higher probability of occurrence having a greater chance of selection. For IDUs with water rights, the irrigation decision sub-model uses a similar process to set the irrigation decision for the year. The characteristics of an IDU that affect irrigation decisions include variable characteristics such as early season precipitation. The probability functions used in the crop and irrigation decision sub-models were derived from empirical data including numerous GIS data sets, and data collected in a survey of > 500 Willamette valley farmers about their irrigation and planting decisions between 2007-2012.

Key Data Sources and Assumptions

Links to additional Documentation















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