May 23 - July 29
Impact of Rain Gauge Location Errors on Verification of Radar-Based Precipitation Estimates
Sebastian Harkema, Heather Grams, and Steve Martinaitis
What is already known:
- The Multi-Radar Multi-Sensor (MRMS) system, which generates a 1-km grid of quantitative precipitation estimates (QPE) products, can provide insight to forecasters when issuing flash flood warnings.
- Rain gauges are treated as ground truth and can provide the most accurate verification of radar-based QPE.
- Verification and data accuracy using gauges is only as good as the instrumentation and observations. Even with the advancement of technology, inaccuracies of rain gauges persist and are well documented.
What this study adds:
- It is standard to accept that radar-based QPE values can vary from collocated observed gauge values; however, location errors with rain gauges can have an impact on the verification of MRMS QPE.
- A majority of Automated Surface Observing System (ASOS) stations in the Continental United States (CONUS) were found to be in a different MRMS grid box than the one indicated by the latitude and longitude in their original metadata.
- New QPE values based on the new latitude and longitude coordinates had better correlation with the observed precipitation than those QPE values based on the original metadata locations.
Abstract:
Flash flooding can cause hundreds of deaths and billions of dollars worth of damage each year. In 2015, there were 176 fatalities in the United States, Puerto Rico, Guam and Virgin Islands, which is roughly five times higher compared to those caused by tornadoes. The Multi-Radar Multi-Sensor (MRMS) system, which generates a 1-km grid of quantitative precipitation estimates (QPE), can provide insight to forecasters when issuing flash flood warnings. The most accurate data are needed for the high spatial resolution of MRMS. Rain gauges are treated as ground truth and can provide the most accurate verification of QPE. The most well-known gauge network is the 838 rain gauges from Automated Surface Observing System (ASOS) stations. It is a standard to accept that QPE values can vary from collocated observed gauge values however, location errors of the rain gauge can have an impact on the verification of MRMS QPE. Using Google Earth, it is determined that ASOS location errors varied from less than 3 m to 80,163 m. The locations errors resulted in 79.31% of ASOS stations in the CONUS to be in a different MRMS QPE grid box. Of those stations, 19.44% were found more than 1 km away from the expected locations. QPE values for the new and old locations were compared to observed precipitation data with the correlation increasing from 0.777 to 0.810. This comparison highlights the need to update rain gauge metadata to improve the verification of radar-based QPE and other hydrometeorological products.