Investigating Instrumental and Environmental Contributions to Microscale Rain Gauge Variability

Heavy rainfall frequently causes flash flooding in low-lying areas of the southeastern United States. High quality surface rainfall measurements are critical for providing ground truth comparisons for quantitative precipitation estimates derived from radar and satellite imagery. This research examines instrumental variability among 13 individual rain gauges located in an 8.5 by 13 meter area at the University of Louisiana at Monroe, focusing on the comparison between a tipping bucket rain gauge and two Community Collaborative Rain, Hail, and Snow network (CoCoRaHS) rain gauges. Seven of the CoCoRaHS gauges are deliberately sited within 3 meters of obstructions to quantify how much rainfall is underestimated relative to the two control rain gauges that are better sited.

Environmental factors that may contribute to inconsistencies among rain gauge measurements like wind speed, wind direction, rain rate, and storm type are also analyzed. Emphasis is placed on correlating the maximum, mean, and standard deviation of wind speed with the corresponding variability in rain gauge measurements. Time series from a few diverse case studies will also be presented to better understand these variations, including rainfall from Hurricane Isaac on 30 August 2012 and a frontal heavy rain event (> 150 mm) on 29-30 September 2012. This research supplements previous studies in improving our understanding of environmental and instrumental factors that contribute to natural gauge variability and estimation errors, particularly in heavy rain events.