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Climate <br />Accurate estimation of ET requires climate data, such as precipitation; monthly mean <br />? <br />temperature; minimum, maximum and dew-point temperature; wind run; and solar radiation <br />(depending on the ET estimation method). The SCS Blaney-Criddle methods use precipitation <br />and monthly mean temperature to estimate ET. The Penman-Monteith methods use daily <br />precipitation; minimum, maximum, and/or dew-point temperature; wind run; solar radiation; <br />and daylight hours. <br /> <br />The effective precipitation is the actual amount of precipitation available for use by plants. <br />? <br /> <br />In the CU model interface, the user has the option to select climate stations for the area and <br />? <br />weight them depending on the location and the method being used. <br />Elevation <br />Elevation is considered at the site of the weather station for the SCS Blaney-Criddle methods <br />? <br />and the Penman-Monteith methods. <br />Water Supply <br />Naturally, unless water is available from precipitation, groundwater, or irrigation, crops cannot <br />? <br />consume water. In areas of the arid and semi-arid West, such as the Western Slope of <br />Colorado, the major source of water is irrigation. In these areas, the quantity and seasonal <br />distribution of the available water supply affect the consumptive use characteristics of <br />agricultural land. <br />Soil Characteristics <br />Soil characteristics are important for estimating ET rates. These characteristics include field <br />? <br />capacity and permanent wilting point that together define the water holding capacity (AWC) of <br />the soil, an important parameter in determining a soil moisture budget. The drying <br />characteristic of the soil is also an important factor in estimating the wet soil evaporation. All <br />of these characteristics can be determined by the type of soil. Soil type varies with depth, <br />therefore the CU model uses an average soil AWC. Rather than selecting the soil AWC in the <br />first layer, which may not compose the majority of the root zone, an average soil AWC for all <br />the layers has been developed using some of the GIS data. See Task Memorandum 1.14-17 for <br />this methodology. <br />Plant Growth Characteristics <br />Plant growth characteristics define stages for the water use characteristics during different <br />? <br />times in the plant's development. These stages include the emergence and development of <br />complete vegetative cover, the period of maximum vegetative cover, and the maturation stage. <br />One of the main considerations is the dates of harvesting and planting. These dates can be <br />expected to change depending on local conditions. Therefore, dates have been developed for <br />the Gunnison River basin. Table 1 shows the crops for which complete data is currently <br />available. The sources for the information in Table 1 are different depending on the crop type <br />3 <br />A275 01.09.95 1.14-9 Lange <br />