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Consumptive Irrigation Requirement Method <br />Consumptive irrigation requirement (CIR) is defined by Soil Conservation Service (SCS) TR-21 as "the <br />depth of irrigation water, exclusive of precipitation, stored soil moisture, or ground water, that is required <br />consumptively for crop production." This value essentially serves as the consumptive use value that can <br />be expected for a particular agricultural land area. <br />Model Specific Data Requirements <br />Some of the models have data that are required in addition to the data requirements of the methods used <br />to estimate evapotranspiration. These criteria consider the types of data required and how difficult it <br />may be to obtain these data. <br />Can Crop Coefficients Be Added or Changed? <br />In anticipation of developments in irrigation science and needs of the CRDSS modelers, the model <br />selected should have the option to change or add different consumptive use crop curves or coefficients. <br />This is essential for the consumptive use (CU) model to be transferable throughout the entire CRDSS <br />study area. <br />Are Crop Coefficients Basal or Mean? <br />Some of the models included reference crop methods. The reference crop methods can use two types of <br />crop coefficients: (1) basal crop coefficients that separately consider evaporation from soil and <br />transpiration from plants, and (2) mean crop coefficients that consider a mean value of consumptive use <br />for both losses. <br />Can the Model Accurately Estimate Evapotranspiration for Alfalfa and Meadow Grass? <br />A large percentage of Colorado's agricultural land is alfalfa and meadow grass. The consumptive use <br />estimates for these categories are critical to accurately predict water use by evapotranspiration. <br />Can the Model Be Locally Calibrated? <br />Can the model be calibrated for use in small areas and then applied to the entire CRDSS area? <br />Can the Model Be Used for the Entire CRDSS Area? <br />The model should be flexible enough to apply to all of the different conditions and crop types that are <br />found in the CRDSS area. The usability is a measure of this flexibility. <br />Does the Model Reduce Evapotranspiration When the Water Supply is Limited? <br />During times when the soil moisture is low, the evapotranspiration rate of plants is reduced. It is <br />important that a model be capable of adjusting evapotranspiration at times when available soil water is <br />limited. <br />2 <br />A275 01.09.95 1.14-3 CSU IDS <br />