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Selecting Time Periods <br />The CU model allows the user to select one or multiple years and to view averages and/or portions of a <br />year to determine peak irrigation periods from the model's output (1975 -1992 is the period of record that <br />is available). <br />Selecting Input Data <br />The CU model interface uses a data management interface (DMI) to retrieve data. The GRASS- <br />INFORMIX link uses location and spatial extent for the area selected and retrieves corresponding data <br />from the database, such as population densities, elevation, crop-type, and other spatial data. The DMIs <br />access the various databases and return non-s patial data needed for modeling, such as crop <br />characteristics, planting dates, livestock water use characteristics, reservoir characteristics, weather time <br />series, etc. These data and corresponding attributes are passed back to the CU model interface and a <br />consumptive use amount is calculated. Task Memorandum 1.14-2 details the CU model input <br />requirements. <br />The CU model program (run_cu) uses inputs flat files, which are simply ASCII text files. The underlying <br />computational features are developed in FORTRAN. These features allow the user to prepare standard <br />input files that are text-based and can be run without the CU model interface. The standard input files <br />include comments, labels, and titles for all the components in the file itself. Man pages are available for <br />these input files and can be accessed by typing "man cu_input" at the command line. <br />Data Inputs for Irrigated Lands <br />The user is able to select the Soil Conservation Service (SCS) Blaney-Criddle or the Penman-Monteith <br />evapotranspiration (ET) estimation methods for irrigated lands. Agricultural consumptive use is <br />primarily water use by crop ET. ET is the amount of water used by vegetation growth and evaporation <br />from adjacent soil or plant foliage. The user can specify the original SCS Blaney-Criddle or the <br />enhanced version. The enhanced SCS Blaney-Criddle method includes a soil moisture budget that <br />accounts for the effective precipitation during winter. Similarly, the Penman-Monteith reference crop <br />option allows the user to select alfalfa or grass as the reference crop. <br />A planting and harvesting date can be entered by the user with minimum mean temperatures for the <br />beginning and end of the season. Default values are available for each crop. <br />Detailed soil data are included (for example, each combination of crop type and soil type are saved for <br />analysis). The soil data is used to keep track of a soil moisture budget year-round. <br />The accuracy of ET estimates depends on collecting good, representative meteorological and other data <br />and accurately selecting a portion of the data to be used for ET estimation (i.e. correctly selecting the <br />data representative of the land area to be estimated). The accuracy of ET estimation also depends heavily <br />on the physical laws governing the processes of ET from crops. The most important data for estimating <br />ET are climate, elevation, water supply, and plant growth characteristics. These are specified in Task <br />Memorandum 1.14-2. <br />2 <br />A275 01.09.95 1.14-9 Lange <br />