11-Thiessen—Software for Automatic Estimation of Weighted Average Rainfall.

Abstract

Estimation of average areal rainfall from point measurements is the first most important step in hydrological modelling. The Thiessen polygon method is commonly used for the purpose. This paper presents the development and usage of a MS Windows based software for estimation of weighted average rainfall over a basin using Thiessen Polygon Method. The software requires the vertex points of the basin boundary described by a polygon, location of raingauges as points and the monthly rainfall data at all the raingauges. The software uses a vector method, which is very fast and accurate, for the estimation of Thiessen weights depending on data status (availability of data at different gauges) of the basin for a specific month. Then it computes the average rainfall over the basin using the estimated weights. Along with the weighted average rainfall series, the software also gives other useful information as output such as data status at the gauges, Thiessen weights and Thiessen polygon in graphical form for different combination of gauges etc. There is provision for saving the text output in simple text as well as in popular spreadsheet (Excel) format, and the graphical output in commonly used graphical formats (bmp, tif, jpg, png, emf and wmf). In a case study the software is used to estimate the monthly weighted rainfall of a basin for 105 years, which it completed in 35 seconds on a Pentium IV PC.