Selecting parameter values for the AWBM daily rainfall-runoff model for use on ungauged catchments

A new method of calibration of the Australian Water Balance Model (AWBM) daily rainfall-runoff model allows for errors in the estimation of areal rainfall over the catchment. The result of applying the method to a group of gauged catchments is the production of a single set of parameter values for the AWBM that can be used with any catchment in the group, or used to estimate runoff on ungauged catchments in the same locality. The method is demonstrated on 121 catchments, comprising groups in five States of Australia from the tropics to temperate zones and over a wide range of catchment sizes and runoff characteristics. With adjustments to input rainfall of less than 20%, the average annual runoff from any catchment in a group can be reproduced by a single set of parameter values to any required degree of precision. The ability of a single set of parameter values to estimate average annual runoff from a group of catchments with only small adjustments of input rainfall raises doubts about the ability to determine the effects of catchment characteristics on runoff with current rainfall-runoff data sets.