Undercatch of tipping-bucket gauges in high rain rate events

C E Duchon,C J Biddle

doi:10.5194/adgeo-25-11-2010

Abstract

Abstract. We have investigated differences in rainfall accumulations for seven high rain rate events from three gauges: a Geonor T-200B vibrating-wire weighing gauge and two MetOne tipping-bucket gauges. The Geonor gauge and one tipping-bucket gauge are located in a pit so that their collection orifices are at ground level. Thus their measured rainfall accumulations are minimally affected by wind speed. The other tipping-bucket gauge is located 105 m from the pit and is surrounded by an Alter-type slatted wind screen. Its collection orifice is positioned 1 m above ground level. The results from the seven events show that the tipping-bucket gauges noticeably underestimated storm event rainfall totals relative to the weighing-bucket gauge when 1-min rain rates exceeded about 50 mm/h (2 in/h). In addition, we conclude that observable wind induced undercatch by the aboveground tipping bucket gauge begins when the wind speed at a height of 2 m exceeds around 5 m/s. In this paper we show and discuss time series of rain rates, differences in rain rates, and wind speeds for two of the seven events in an attempt to account for the lower storm totals from the two tipping bucket gauges relative to the weighing-bucket gauge.

Highlights

It is well known that tipping-bucket gauges undercatch the actual amount of rain as the rain rate increases
In this paper we show and discuss time series of rain rates, differences in rain rates, and wind speeds for two of the seven events in an attempt to account for the lower storm totals from the two tipping bucket gauges relative to the weighing-bucket gauge
In this paper we show and discuss time series of rain rates and wind speed during two high rain rate events from among the seven we studied

Summary

Introduction

It is well known that tipping-bucket gauges undercatch the actual amount of rain as the rain rate (or rain intensity) increases. The motivation for our investigation is that, we want to develop an algorithm for correcting tipping-bucket measurements of rainfall given the elapsed time between successive tips. Both laboratory and field observations will be used to determine the magnitude of undercatch. In the first case presented here, we had only two gauges: the weighing-bucket gauge in the pit and an aboveground tipping-bucket gauge We present this case, though, because of the persistent high rain rates that resulted in substantial undercatch from the tipping-bucket gauge

Description of field site and data acquisition

High rain rate events

Findings

Conclusions from these and other high rain rate events