Implications of using Precipitation from NOAA Atlas 14

Abstract Only - Regulators and Consultants currently rely on rainfall intensities and total rainfall values published in the National Weather Service (NWS) Hydro-35 (Hydro-35) and Technical Paper No. 40 (TP-40) to design and analyze Water Resource and Storm Water Infrastructures throughout the country. Hydro-35 and TP-40 were developed in the early 1960’s with a period of record from 1938 to 1957. According to scientists, Hydro-35 and TP-40 cannot be relied upon, because the dataset does not include most current precipitation data and it may underestimate runoff. The National Oceanic Atmospheric Administration (NOAA) had updated Hydro-35 and TP-40 for the whole country and NOAA has indicated that Atlas 14 has replaced Hydro-35 and TP-40.

This study investigated the potential implications associated with using the rainfall intensities and total rainfall values published in NOAA Atlas 14 for the design of Water Resource and Storm Water Infrastructures in various states throughout the United States. As part of this study, rainfall values from the NWS TP-40 and NOAA Atlas 14 for 12 states were compared to each other. Of the 12 states, three states are from the Northeast, two from the Mid-Atlantic, two from the southeast, two from the Ohio River Valley, one from the Southwest, and one from Northwest. This study also investigated the implications of using NOAA Atlas 14 when evaluating a common detention pond design example using a combination of a Microsoft Office Spreadsheet developed by the Natural Resource Conservation Service (NRCS) and the Army Corps of Engineers (ACOE) Hydraulic Engineering Center (HEC) Hydrologic Modeling System (HMS) Computer model. The design example was originally evaluated using TP-40 rainfall values.