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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