463 - How Does Rain-gauge Network Density and Resolution Affect Hourly and Sub-hourly Rainfall Frequency Estimates? An Analysis Using High Spatio-temporal Resolution Rainfall Data

Gauge-measured point precipitation maxima are used for estimating extreme rainfall quantiles through frequency analysis, yielding Depth-Duration-Frequency (DDF) values. Over shorter durations these extreme events are often convective, displaying a restricted geographical footprint. This makes it highly unlikely that they will be captured by the coarse-resolution rain-gauge network that we have in the United States, with a low spatial density of stations, most of which totalize every 15 minutes. Therefore, our objective is to elucidate the uncertainty and bias we introduce when estimating DDF values, due to the low spatio-temporal resolution of the U.S. rain-gauging network. To do so, we use a network of 862 gauges operated by the German Weather Service, which is one to two orders of magnitude denser, providing 13 years of 1-min resolution rainfall. We aim to understand how different the DDF values would be, if Germany had the same type of rainfall data that we use here. We explore the spatial density effects by generating many realizations of lower-density networks, and those of time-resolution by aggregating the 1-min data over 15-min fixed windows, investigating both effects separately and jointly. For each density-resolution realization, we mimic the procedures for regional frequency analysis adopted in NOAA Atlas 14, but using partial duration series, and then compare the rainfall quantiles to the “true” DDF values obtained for the full dataset. For each combination of return period and rainfall duration, we present our results as distributions of the differences and as maps of the bias and uncertainty in DDF values.