Comparative rainfall observations from pit and aboveground rain gauges with and without wind shields

A study of rain gauge observations was initiated in 1995 to assess the magnitude of undercatch due to wind and the effect of reducing undercatch using an Alter-type wind shield. The observation site was near the Norman, Oklahoma, airport with good exposure in all directions. The experimental setup comprised three tipping-bucket rain gauges, three weighing-bucket rain gauges, and anemometers at 1 and 2 m. For each type of gauge, one was placed in a pit with its orifice at ground level, and the other two were placed above ground, one with an Alter shield and one without. One-minute rainfall accumulations and wind speed averages were obtained from 101 rainfall events over 30 months. The results show that for typical rainfall events, the undercatch of the unshielded tipping-bucket rain gauges was 4% relative to the tipping-bucket pit gauge. The comparable figure for the unshielded weighing-bucket gauge was 5%. Both Alter-shielded gauges showed less than a 1% reduction in undercatch relative to the unshielded gauges for typical rainfall events, We discuss the sources of errors that can be expected in similar rain gauge measurements when the gauges are properly maintained.