COMMAND AREA WATER DEMANDS .2. WATER-DEMAND FUNCTION

The cumulative water demand (CWD) curve was used for validating and ca librating the unit command area (UCA) model, which predicts the aggreg ate water demands of individual command areas for the entire crop seas on. During the model calibration process, as presented in the companio n paper, three important variables in the operation stage on the predi ction of demand were found to be dominant in determining the CWD curve profile. The logistic function with three parameters, which is a part icular form of the exponential-type function, was adopted for fitting the CWD curve. High correlations,were observed between the individual curve parameters and the field variables. Three parameters are managem ent-allowable depletion (MAD), irrigation application uniformity (IAU) , and initial soil moisture (ISM). Effectiveness. of the equation deve loped for a particular UCA using the regression analysis was successfu lly demonstrated, and applicability for some other UCAs in the same wa ter system was also recognized.