The relationship between observation intervals and errors in radar rainfall estimation over the Indochina Peninsula

Abstract

Although several meteorological radars are operated routinely in Southeast Asian countries, their observation frequencies are sometimes only one or two times per hour. To examine the usability of such poorly sampled observation data, this study investigated the relationship between the observation interval and the estimation error of radar rainfall intensity. The data sets analysed were the radar reflectivity data obtained from the Om Koi S-band radar located in northern Thailand, which operates at approximately 5-min intervals, and the surface rainfall data of rain gauges installed in the Mae Chaem Watershed, which has a catchment area of 3853km 2. Through the calibration of parameters in a relationship equation between the rainfall intensity and the reflectivity, hourly rainfall intensities were estimated successfully with high accuracy. The reflectivity data with a poor temporal resolution were constructed by resampling the original 5-min-interval data. The comparison of hourly rainfall intensities estimated from the resampled data with those from the original data reveals that the root mean square error can be expressed as a function of the observation interval and grid size of the radar rainfall intensity product. We conclude that even 30-min intervals of reflectivity data are useful for estimating the average hourly rainfall intensity over the Mae Chaem Watershed. © 2011 John Wiley & Sons, Ltd.