1. Design Rainfall Distributions Based on NRCC Data

2. NRCC Rainfall Distributions October 2015 General Considerations Standard NRCS rainfall distributions were developed between 1960 and 1985. NRCS is adopting NRCC rainfall data in the states where it is applicable. Will a new set of rainfall distributions be required ? If so, how to develop and apply them ? 2

3. NRCC Rainfall Distributions October 2015 Standard Rainfall Distributions 3

4. NRCC Rainfall Distributions October 2015 Geographic Application 4

5. NRCC Rainfall Distributions October 2015 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. 5

6. NRCC Rainfall Distributions October 2015 Example of a Nested Distribution 3 hr 0.6 6 hr 0.7 6

7. NRCC Rainfall Distributions October 2015 NRCC web site Download rainfall frequency data at: http://www.precip.net/ 7

8. Select Data & Products Tab NRCC Rainfall Distributions October 2015 8

9. Select GIS Data Files NRCC Rainfall Distributions October 2015 9 Select GIS Data Files Select 60-min 25-yr layer Select 24-hr 25-yr layer

10. NRCC Rainfall Distributions October 2015 Prepare GIS layers 10 60-minute 25-year precipitation 24-hour 25-year precipitation

11. NRCC Rainfall Distributions October 2015 Compute 60-min / 24-hr Ratio 11

12. NRCC Rainfall Distributions October 2015 Ratio for each Distribution Region 12

13. NRCC Rainfall Distributions October 2015 Four Rainfall Distribution Regions 13

14. NRCC Rainfall Distributions October 2015 Unsmoothed ratio for each duration based on 25-yr rainfall 14

15. NRCC Rainfall Distributions October 2015 Smoothed ratio for each duration based on 25-yr rainfall 15

16. NRCC Rainfall Distributions October 2015 Final Rainfall Distribution Map 16

17. NRCC Rainfall Distributions October 2015 Rainfall Distribution Plots 17

18. NRCC Rainfall Distributions October 2015 Future Directions NRCC data may be imported into WinTR- 20 Version 3.10. When NOAA Atlas 14 for New York and New England states is completed, NOAA Atlas 14 will be adopted by NRCS. Most likely, new rainfall distributions and maps will be developed. 18

19. NRCC Rainfall Distributions October 2015 19