Examination of extreme value precipitation distribution from a high density CoCoRaHS network compared to a long-record National Weather Service Cooperative station

The Community Collaborative Rain, Hail and Snow network (CoCoRaHS) now has several years of data with large numbers of volunteer precipitation measurements across the U.S. In some areas the concentration of stations is very high -- approaching one station per 3 km2 in a few areas. This study examines the characteristic of daily precipitation extreme values in five regions of the country where there is a high density of CoCoRaHS stations in close proximity to a long-record (100 years or greater) individual station. It will be shown that extreme value distributions needed to estimate design rainfall for engineering and planning applications can be derived from these high density short duration records. The uncertainty of these estimates will be assessed and the years of record needed to reduce this uncertainty will be evaluated.