Evaluation of Satellite Precipitation Products in the Chehalis River Basin during Winter 2015-2016 Using OLYMPEX Data

A primary goal of the Global Precipitation Measurement (GPM) satellite is to provide a basis for hydrologic predictions, especially in areas where in situ measurements are sparse. We evaluated the GPM-based IMERG product in the Chehalis River Basin, WA, where flood peaks are almost exclusively associated with cold season precipitation, but the snowmelt contribution to runoff is mostly modest. We constructed estimates of hourly precipitation at 1/32-degree spatial resolution over the entire basin using a combination of NOAA WSR-88D precipitation radar (mostly from the Langley Hill radar on the Washington Coast), and gauge estimates as incorporated in NOAA’s National Severe Storms Laboratory (NSSL) gauge-corrected radar QPE product.  We augmented the NSSL QPE product with an additional 25 gauges that were operational during at least half of the OLYMPEX period Nov 1 2015 - Mar 31 2016. Among the supplemental gauges, 10 were dual-platform rain gauges installed especially for OLYMPEX, and the remainder are from a combination of NOAA’s Cooperative Observer network, CoCoRaHS, and ASOS. We evaluated IMERG precipitation through comparison with our merged data set, and we evaluated the UWMAFS product (based on a nested implementation of the WRF regional atmospheric model) as well a range of temporal resolutions including hourly, 3-hourly and daily. We also compared predictions of two modest floods during the OLYMPEX period using the Distributed Hydrology-Soil-Vegetation model forced with our merged data set, IMERG, and UWMAFS.