A Comparison of Rainfall Estimation Techniques

Abstract

This study compares two techniques that have been developed for rainfall and streamflow estimation with the aim of identifying strengths and weaknesses of each. The first technique utilises thin plate smoothing splines to develop rainfall surfaces for the catchment, which are then, in conjunction with daily point-wise rainfall data used to determine areal catchment estimates. The second technique develops a regression-based model relating elevation to total annual rainfall in order to scale rainfall for daily mean catchment rainfall estimates. Both approaches are compared in common catchments in the upper Murrumbidgee catchment. The comparison includes using the data from each of the approaches as input to a rainfall-runoff model and by comparison of the quality of modelled results to observed streamflow. The strengths, weaknesses and use for catchment managers in decision making are identified. The study results revealed that where rain station spatial density and data quality are high, both regression and the spline method perform equally as well in estimating long term rainfall trends. In conclusion, catchment managers could apply the simple regression technique over the sophisticated spline method to achieve the comparable results. This is particularly useful where an efficient yet simple method is required for assessing streamflow within similar catchments.