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BSTRACT A probability model for predicting the occurrence and magnitude of thunderstorm rainfall developed in the southwestern United States was tested in the metropolitan Chicago area with reasonable success, especially for the moderate to the extreme runoff-producing events. The model requires the estimation of two parameters, the mean number of events per year and the conditional probability of rain given that an event has occurred. To tie in the data from more than one gage in an area, an event can be defined in several ways, such as the areal mean rainfall exceeding 0.50 inch and at least one gage receiving more than 1.0 inch. This type of definition allows both of the model parameters to be obtained from daily warm-season rainfall records. Regardless of the definition used a Poisson distribution adequately described the number of events per season. A negative binomial distribution was derived as representing the frequency density function for rainfall where several gages are employed in defining a storm. Chicago data fit both distributions very well at events with relatively high return periods. The results indicate the possibility of using the model on a regional basis where limited amount of data may be used to estimate parameters for extensive areas. [ABSTRACT FROM AUTHOR]

In the calibration of aquifer models, the desire for an automated adjustment process is sometimes in conflict with the need for subjective intervention during the calibration process. Working from the established concept of modeling for unconfined aquifers with rectangular nodes, this paper describes a method of obtaining subjective information in addition to that customarily used in model calibration. Such information is assembled and quantified at the same time as the usual data are gathered for initial estimation of parameters. This information is then introduced into an automatic adjustment process in such a way that the calibration process can proceed without interruption until the desired level of relative accuracy is reached, or until it is shown that the desired level cannot be reached within the constraints assigned. A decoupling technique that permits (under restricted conditions) simultaneous adjustment of all parameters is also described. A digital computer model of the Tucson basin aquifer is used to illustrate the concepts and demonstrate the adjustment method. [ABSTRACT FROM AUTHOR]