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2019 Rainfall Data Update (Published in 2022)

The New Jersey Department of Environmental Protection has released a study performed by the Northeast Regional Climate Center, a National Oceanic and Atmospheric Administration (NOAA) partner, confirming increases in precipitation across New Jersey over the last 20 years. The study, Changes in Hourly and Daily Extreme Rainfall Amounts in NJ since the Publication of NOAA Atlas 14 Volume, closes climate data gaps and addresses how measures of storm intensity have changed by incorporating the past two decades of data into the current analyses. The data show that the current version of NOAA Atlas 14, published in 2006 with data through 1999, does not accurately reflect current precipitation intensity conditions particularly for 24-hour and 48-hour storm events. This study updated the dataset up to 2019 with data collected from weather stations in NJ, NY, and PA. The report provides adjustment factors for the precipitation depth of the weather stations utilized in the report. The report of this study is available at The Department further utilized the adjustment factors from the weather stations to produce the adjustment factors of precipitation depth by county. The adjustment factors by county, reflecting the rainfall dataset up to 2019, are available here.

photo: rain clo	udsChanges in Rainfall Data and the Use of the Delmarva Unit Hydrograph (Published in 2012 for rainfall dataset up to 1999)

Based upon recent updates to the rainfall amounts for specific storm events, the National Weather Service has provided updates of the rainfall frequency data available at The Natural Resources Conservation Service (NRCS) provided precipitation depths based on NOAA Atlas 14 (rainfall dataset up to 1999) for New Jersey available by county at (pdf).

The NRCS, in the supplement attached to the New Jersey Bulletin No. NJ210-3-1, dated September 8, 2003, states that the use of the Delmarva Unit Hydrograph may be used in modeling watersheds in the Coastal Plain Region of New Jersey “that are characterized by flat topography (average watershed slope less than 5 percent), low relief, and significant surface storage in swales and depressions.” Use of the Delmarva Unit Hydrograph will not affect the determination of runoff volume, but should result in lower peak discharges when compared to the Standard Unit Hydrograph. For developed sites or heavily urbanized areas in the Coastal Plain of New Jersey, care should be taken to determine whether the use of the Delmarva Unit Hydrograph is consistent with the conditions above.

All applications requiring runoff computations, under the Stormwater Management Rules at N.J.A.C. 7:8-5.6(a), are required to utilize the new rainfall amounts and the Delmarva Unit Hydrograph, where appropriate, effective September 1, 2005. For applications that have been deemed complete by the Department’s Land Use Regulation Program or the municipality under a municipal review, prior to September 1, 2005, the applicant has the choice of rainfall amounts or unit hydrograph method, provided there is consistency of use throughout the application.

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Last Updated: July 22, 2022