Field accuracy of Canadian rain measurements

Abstract

Daily historical rain-gauge data from several Canadian sources and field experiments were compared to the World Meteorological Organization (WHO) pit gauge rainfall measurements in order to determine the accuracies for different operational rain gauges. The detailed technical description of the main Canadian precipitation gauges assisted in understanding the associated accuracies and the need for adjustments for rain-gauge errors. All gauges, including the pit gauge, reported less than the actual rainfall. The corrections for wind, funnel wetting, evaporation and receiver retention improved the overall accuracy of the manual gauges. The range of rainfall measurements from different manual gauges was greatly reduced after applying the correction factors which were determined through a series of precision measurements. The recently introduced Hydrological Services TB3 tipping bucket rain gauge and the Geonor T-200B precipitation gauge improved rainfall catch efficiencies compared to the older Meteorological Service of Canada (MSC) tipping bucket and F&P/Belfort gauges with error values of -3.5% for the TB3 and -4.7% for the Geonor. The manual Type B gauge, in service for more than thirty years, was found to be the best rain gauge and provided the most accurate values based on all the reported rainfall field experiments with an average bias of only -0.6% compared to the raw pit gauge data.