Lessons Learned from 11 Years of Rain Gauge Intercomparisons Across Oklahoma Including Measurements at Ground Level

Daily rainfall intercomparisons have been made, and continue to be made, at a number of locations across the varying geography and climate of Oklahoma among four different types of widely used rain gauges: a 12-in diameter tipping-bucket gauge, an 8-in diameter tipping-bucket with syphon gauge, a 4-in diameter manual gauge, and a 6.28-in diameter vibrating wire weighing-bucket gauge. The overall purpose of this program was to analyze observations from identical gauges arranged in a group and from different types of paired gauges (a) inside and outside a standard Alter shield and (b) aboveground and within a pit. Events involving frozen precipitation are not considered since none of the gauges are heated and blowing snow can render the ground level observations meaningless. Some of the lessons learned from this long-term effort are: (1) a fair comparison between or among gauges requires a number of seasons of data; (2) collocated, perfectly calibrated gauges seldom report identical rainfall amounts; (3) metadata are vital for multi-year intercomparisons to account for malfunctioning gauges; (4) a group of closely spaced gauges yields a range of rainfall amounts; (5) no single gauge can be considered the "truth" in every rain event; and (6) large differences between aboveground and ground level gauges can occur in high rain rate and high wind speed conditions. We will support these conclusions by showing comparative graphical analyses of daily rainfall coupled with physical arguments.