How much rain does a rain gage gage?

Abstract

Rain gages of various sizes and shapes have been used for hundreds of years to measure the amount of rain that actually reaches the ground surface. In this study, I compared rainfall data from four locations for gages normally exposed with their orifices about 1 m (40 in.) above ground with control gages installed with their orifices at the ground surface. The normally exposed gages caught between 5 and 15% less rain for all rainfall events than did the control gages. For single rainfall events, where the total catch exceeded 12 mm (0.5 in.), the error ranged between 0 and 75%, depending on wind characteristics during the storm. Attempts to develop a correction procedure based on conventional wind measurements were unsuccessful. It was concluded that the most expedient way to accurately measure rainfall in windy environments is with pit gages, which eliminate all wind effects.