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Design Rainfall Distributions Based on NOAA Atlas 14

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WinTR-20 NOAA 14 Data March 2009 2 General Considerations Standard NRCS rainfall distributions were developed between 1960 and 1985. NRCS is adopting NOAA Atlas 14 in the states where it is applicable. Will a new set of rainfall distributions be required ? If so, how to develop and apply them ?

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WinTR-20 NOAA 14 Data March 2009 3 Standard Rainfall Distributions

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WinTR-20 NOAA 14 Data March 2009 4 Geographic Application

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WinTR-20 NOAA 14 Data March 2009 5 Steps in developing a distribution Determine ratios of x hour / 24 hour rainfall. Place the rainfall ratio for the shortest duration in the center of the distribution. Symmetrically place each larger duration to include the shorter durations.

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WinTR-20 NOAA 14 Data March 2009 6 Example of a Nested Distribution 3 hr 0.6 6 hr 0.7

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WinTR-20 NOAA 14 Data March 2009 7 NOAA Atlas 14 web site Download rainfall frequency data at: http://hdsc.nws.noaa.gov/

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WinTR-20 NOAA 14 Data March 2009 8 Select State

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WinTR-20 NOAA 14 Data March 2009 9 Selected Ohio

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WinTR-20 NOAA 14 Data March 2009 10 Selected Columbus Ohio

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WinTR-20 NOAA 14 Data March 2009 11 NOAA 14 Rainfall Ratios

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WinTR-20 NOAA 14 Data March 2009 12 Symmetrical Distribution

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WinTR-20 NOAA 14 Data March 2009 13 Compare to Type II

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WinTR-20 NOAA 14 Data March 2009 14 Where Type II and Type III compare with NOAA- derived distribution, 25-yr rainfall Purple: Type II Pink: Type III Green: both

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WinTR-20 NOAA 14 Data March 2009 15 Points used to represent Maryland Counties

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WinTR-20 NOAA 14 Data March 2009 16

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WinTR-20 NOAA 14 Data March 2009 17

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WinTR-20 NOAA 14 Data March 2009 18 Future Directions Develop software to easily use the data. Use GIS data layers to derive site-specific rainfall data for hydrologic modeling.

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WinTR-20 NOAA 14 Data March 2009 19

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