The representation of storm precipitation fields near ground level

The patterns of precipitation near the ground surface during a storm can be described by a ‘filtered input field,’ which is amenable to mathematical statement and analysis. The filtered input field is generated by a process of smoothing of recording rain gage data, and it reveals the trends of the storm that are significant from the hydrological standpoint. For this purpose, techniques of curve and surface fitting based on the use of the three-parameter gamma distribution and low-order nonorthogonal polynomials were developed and applied to the analysis of precipitation events over a California watershed. It is believed that these methods can be used for the establishment of criteria for precipitation network design and for the analysis of watersheds as nonlinear systems with distributed input fields.