An analysis of the National Water Model for a mid-Atlantic suburban watershed

ABSTRACTDischarge values from the National Water Model (NWM) were compared to USGS stream gage discharge observations for the suburban Red Clay Creek watershed (drainage area ~140 km2 and mixed land-use), in Pennsylvania and Delaware, from 2016 to 2018. 18-hour retrospective simulations from the NWM were used with concurrent hourly USGS discharge observations from three locations along the Red Clay Creek. Results indicate that the mean of discharge estimates from the NWM and from USGS observations significantly differed and that the NWM generally underestimates low-flow conditions and overestimates high-flow conditions. Watershed size also impacted NWM performance (with performance degrading in smaller watersheds). A meteorological analysis determined that convective rainfall events were associated with 66% of the largest differences between NWM discharge estimates and USGS observations while mid-latitude cyclone stratiform precipitation events accounted for the other 34%. Lastly, of the largest 15 differences between the NWM and observations, 13 occurred with pre-cursor soil moisture that was below the mean (dry soil conditions), in conjunction with heavy rainfall. Given the NWM’s recent operational implementation, and its status as Prototype guidance, the results of this study present specific geographical and climatological findings that can aid in the NWM’s continued validation and improvement for similar regions.KEYWORDS: National water modelstreamflowmid-atlanticwatershed analysisClimatewater Resources AcknowledgmentsThe authors would like to thank the anonymous peer reviewers for their suggestions as well as Kevin Brinson and Chris Hughes for their helpful comments whilst revising this manuscript for publication.Disclosure statementNo potential conflict of interest was reported by the authors.Data availability statementThe authors confirm that data used for this research are publicly available and can be accessed by the links and references provided.Additional informationFundingThis publication was made possible by the National Science Foundation EPSCoR Grant No. 1757353 and the State of Delaware.