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Agricultural Crop Evapotranspiration Data Input <br />The most important factor in determining the expected water use of an agricultural land area is crop <br />evapotranspiration (ET). ET is a combination of water loss through evaporation and plant water use or <br />transpiration. <br />Methods for Estimating Crop ET <br />The Soil Conservation Service (SCS) modified Blaney-Criddle (SCS Blaney-Criddle) will be used. The <br />SCS Blaney-Criddle method has climatic data inputs, such as mean monthly temperature, monthly <br />percentages of sunshine hours, land use data, and some known tables used to determine growing season <br />and crop growth characteristics. <br />Data Needs for Crop Characteristics <br />There are standard values used to calculate crop ET that will be obtained from current literature or <br />references. These values will be used to calculate consumptive use for each crop type. Table 3 displays <br />some of the inputs that will be needed. A set of default values will be provided to the user, but the user <br />will be able to customize these values for particular modeling needs. <br />TABLE 3 <br />AGRICULTURAL CROP ET INPUT DATA FOR EACH CROP TYPE <br />FROM <br />MODEL INPUTUNITSTYPE ENTITY(S) <br />Crop nameUnitless Charactercrop_character <br />Crop growth curve, varies by elevation <br /> (table of values showing a max of 24 pairs)UnitlessPairs include Int and Fl t crop_character <br />Root zoneDepth (Ft ) Floatcrop_character <br />Days to first cut (alfalfa)DaysIntegercrop_character <br />Days between cuts (alfalfa)DaysIntegercrop_character <br />Planting dateDayInteger (1-365)crop_character <br />Harvest dayDayInteger (1-365)crop_character <br />Maximum air temp of earliest moisture useTempFloatcrop_character <br />Minimum air temp. of latest moisture useTempFloatcrop_character <br />Days to full coverDaysIntegercrop_character <br />Data Needs for the User-Specified Area <br />Some input information will be needed depending on the area the user selects to calculate consumptive <br />use. Regardless of whether the user selects an entire river basin, a square area, a number of polygons, a <br />county, a water district, or a combination of all of the above, the same data inputs will be needed for the <br />selected area. These inputs are listed in Table 4. <br />3 <br />A275 01.09.95 1.14-2 Lange <br />