Transformation of point rainfall to areal rainfall by estimating areal reduction factors, using radar data, for Texas

Information about extreme precipitation is of great interest for a variety of purposes, which include dam design and its operation, public safety, engineering projects concerned with river management and drainage as well as rainfall-runoff relations. These require knowledge about the spatial and temporal variability of average rainfall over an area. Design rainfall values are generally expressed in the form of point rainfall intensity values which is the rainfall depth at a location. In order to obtain areal average values for an area, hydrologists and engineers require techniques whereby point rainfall amounts can be transformed to average rainfall amounts over a specified area. This problem of point-to-area rainfall conversion can be addressed using depth??area curves which require the use of areal reduction factors. The derivation of areal reduction factors is a focal issue and has been dealt with in diverse manners. Though the methods of derivation of the areal reduction factors vary, results shown by them are comparable. But all these methods have certain shortcomings in the procedures adopted by them. In this application the analysis is based on radar rainfall values obtained from NEXRAD for the study area of Texas as provided by West Gulf River Forecasting Centre (WGRFC). Using NEXRADradar rainfall data, geographically fixed depth area relationships will be determined. Here the objectives are to develop areal reduction factors using radar data and to identify the potential obstacles that might hinder the use of such data. The values of the factors developed will be finally compared to other studies which have been carried out. This approach aims to mitigate the difficulties faced in the applications of various procedures and the shortcomings of the various techniques used to determine the values of areal reduction factors.