REGIONAL PRECIPITATION-FREQUENCY ANALYSIS AND SPATIAL MAPPING ... - Oregon

REGIONAL PRECIPITATION-FREQUENCY ANALYSIS AND SPATIAL MAPPING OF 24HOUR PRECIPITATION FOR OREGON Final Report

SPR 656

REGIONAL PRECIPITATION-FREQUENCY ANALYSIS AND

SPATIAL MAPPING OF 24-HOUR PRECIPITATION FOR OREGON

Final Report

SPR 656

by Melvin G. Schaefer Ph.D. P.E. and Bruce L. Barker P.E.

MGS Engineering Consultants 7326 Boston Harbor Road NE

Olympia, WA 98506

George H. Taylor CCM Oregon Climate Service, Oregon State University

Strand Agriculture Hall 326 Corvallis, OR 97331

James R. Wallis Ph.D. Yale University

9 Hillhouse Avenue, ML8 New Haven, CT 06511

for

Oregon Department of Transportation Research Unit

200 Hawthorne Ave. SE, Suite B-240 Salem OR 97301-5192

and

Federal Highway Administration 400 Seventh Street, SW

Washington, DC 20590-0003

January 2008

Technical Report Documentation Page

1. Report No.

OR-RD-FHWA-08-05

2. Government Accession No.

4. Title and Subtitle

Regional Precipitation-Frequency Analysis and Spatial Mapping of 24-Hour Precipitation for Oregon

3. Recipient's Catalog No.

5. Report Date

January 2008

6. Performing Organization Code

7. Author(s)

MG Schaefer Ph.D. P.E. (MGS Engineering Consultants) BL Barker P.E. (MGS Engineering Consultants) GH Taylor CCM (Oregon Climate Service) JR Wallis Ph.D. (Yale University)

9. Performing Organization Name and Address

Oregon Department of Transportation Research Unit 200 Hawthorne Ave. SE, Suite B-240 Salem, OR 97301-5192

8. Performing Organization Report No.

10. Work Unit No. (TRAIS) 11. Contract or Grant No.

SPR 656

12. Sponsoring Agency Name and Address

Oregon Department of Transportation

Research Unit

and

200 Hawthorne Ave. SE, Suite B-240

Salem, OR 97301-5192

Federal Highway Administration 400 Seventh Street, SW Washington, DC 20590-0003

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

For this study regional frequency analyses were conducted for precipitation annual maxima in the state of Oregon for the

24-hour duration. A total of 693 precipitation gages in Oregon, southern Washington, western Idaho, northern California

and northern Nevada were included in the study, representing 34,062 station-years of record. A regional analysis

methodology was utilized that pooled data from climatologically similar areas to increase the dataset and improve the

reliability of precipitation-frequency estimates. The regional analysis methodology included L-moment statistics, and an

index-flood type approach for scaling the annual maxima data. L-moment statistics were used to: characterize the

variability, skewness and kurtosis of the data; measure heterogeneity in proposed homogeneous sub-regions; and assist in

identification of an appropriate regional probability distribution.

Spatial mapping techniques were employed for mapping of the precipitation-frequency information. This included spatial

mapping of at-site means, L-moment ratio values of L-Cv and L-Skewness, and mapping of precipitation for selected

recurrence intervals. Procedures were employed to minimize differences between mapped values and observed station

values in a manner that was consistent with the regional behavior of the data and also recognized uncertainties due to

natural sampling variability.

Color-shaded isopluvial maps were developed for the 6-month, 2-year, 10-year, 25-year, 50-year, 100-year, 500-year, and

1000-year precipitation recurrence intervals. Electronic gridded datasets are available for use in creation of GIS

applications that utilize precipitation-frequency information.

A catalog of extreme storms was assembled that lists precipitation events that exceeded a 20-year return period for the

various climatic regions. The information from the storm catalog was also used to conduct seasonality analyses that

identified the occurrence frequency of extreme storms by month. In particular, the seasonality analyses identified those

months that were the most likely and least likely for an extreme event to occur. This information is useful in rainfall-runoff

modeling and can be used in conducting hydrologic analyses throughout the Oregon study area.

17. Key Words

18. Distribution Statement

CLIMATE , PRECIPITATION-FREQUENCY, RAINFALL, SPATIAL MAPPING, 24-HOUR PRECIPITATION, OREGON, WASHINGTON, IDAHO, CALIFORNIA

Copies available from NTIS, and online at

19. Security Classification (of this report)

Unclassified

Technical Report Form DOT F 1700.7 (8-72)

20. Security Classification (of this page)

Unclassified

21. No. of Pages

114

Reproduction of completed page authorized

22. Price

Printed on recycled paper

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