1. Design Rainfall Distributions Based on NOAA Atlas 14

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 ?
Types I, II, and IA were developed in 1960’s. Type III was developed in
WinTR-20 NOAA 14 Data
March 2009

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

4. Geographic Application
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.
WinTR-20 NOAA 14 Data
March 2009

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

7. NOAA Atlas 14 web site Download rainfall frequency data at:
WinTR-20 NOAA 14 Data
March 2009

8. Select State WinTR-20 NOAA 14 Data March 2009
Purtto Rico, the Virgin Islands, and Hawaii now have updated data as well as the areas shown in purple on this map.
WinTR-20 NOAA 14 Data
March 2009

9. Selected Ohio
WinTR-20 NOAA 14 Data
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10. Selected Columbus Ohio
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11. NOAA 14 Rainfall Ratios
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12. Symmetrical Distribution
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13. Compare to Type II WinTR-20 NOAA 14 Data March 2009
At this location, the distribution based on NOAA 14 data is more intense than the Type 2.
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
WinTR-20 NOAA 14 Data
March 2009

15. Points used to represent Maryland Counties
100-year 24-hour rainfall was averaged for each county and a point selected with that rainfall. At the latitude and longitude of each point a NOAA 14 text file was downloaded. Washington and Frederick Counties were split in two parts due to differences in rainfall. The background of this slide is the 100-year 24-hour rainfall GIS grid layer downloaded from the NOAA 14 web site.
WinTR-20 NOAA 14 Data
March 2009

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

19. WinTR-20 NOAA 14 Data
March 2009