HOUR PRECIPITATION for OREGON Final Report
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REGIONAL PRECIPITATION-FREQUENCY ANALYSIS AND SPATIAL MAPPING OF 24- HOUR 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. 2. Government Accession No. 3. Recipient’s Catalog No. OR-RD-FHWA-08-05 4. Title and Subtitle 5. Report Date Regional Precipitation-Frequency Analysis and Spatial Mapping of 24-Hour January 2008 Precipitation for Oregon 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. 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 10. Work Unit No. (TRAIS) Oregon Department of Transportation Research Unit 11. Contract or Grant No. 200 Hawthorne Ave. SE, Suite B-240 Salem, OR 97301-5192 SPR 656 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Oregon Department of Transportation Final Report Research Unit and Federal Highway Administration 200 Hawthorne Ave. SE, Suite B-240 400 Seventh Street, SW Salem, OR 97301-5192 Washington, DC 20590-0003 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, Copies available from NTIS, and online at SPATIAL MAPPING, 24-HOUR PRECIPITATION, http://www.oregon.gov/ODOT/TD/TP_RES/ OREGON, WASHINGTON, IDAHO, CALIFORNIA 19. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 114 Technical Report Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Printed on recycled paper i SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol LENGTH LENGTH in inches 25.4 millimeters mm mm millimeters 0.039 inches in ft feet 0.305 meters m m meters 3.28 feet ft yd yards 0.914 meters m m meters 1.09 yards yd mi miles 1.61 kilometers km km kilometers 0.621 miles mi AREA AREA in2 square inches 645.2 millimeters squared mm2 mm2 millimeters squared 0.0016 square inches in2 ft2 square feet 0.093 meters squared m2 m2 meters squared 10.764 square feet ft2 yd2 square yards 0.836 meters squared m2 m2 meters squared 1.196 square yards yd2 ac acres 0.405 hectares ha ha hectares 2.47 acres ac 2 2 2 2 ii mi square miles 2.59 kilometers squared km km kilometers squared 0.386 square miles mi VOLUME VOLUME fl oz fluid ounces 29.57 milliliters ml ml milliliters 0.034 fluid ounces fl oz gal gallons 3.785 liters L L liters 0.264 gallons gal ft3 cubic feet 0.028 meters cubed m3 m3 meters cubed 35.315 cubic feet ft3 yd3 cubic yards 0.765 meters cubed m3 m3 meters cubed 1.308 cubic yards yd3 NOTE: Volumes greater than 1000 L shall be shown in m3. MASS MASS oz ounces 28.35 grams g g grams 0.035 ounces oz lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb T short tons (2000 lb) 0.907 megagrams Mg Mg megagrams 1.102 short tons (2000 lb) T TEMPERATURE (exact) TEMPERATURE (exact) °F Fahrenheit (F-32)/1.8 Celsius °C °C Celsius 1.8C+32 Fahrenheit °F *SI is the symbol for the International System of Measurement ACKNOWLEDGEMENTS The authors would like to acknowledge Chris Daly of the PRISM Group at OSU who provided the precipitation data layers which formed the basis for the spatial mapping. Cadee Hale of OCS and Joseph Smith of the PRISM Group were involved in collecting daily and hourly precipitation data. DISCLAIMER This document is disseminated under the sponsorship of the Oregon Department of Transportation and the United States Department of Transportation in the interest of information exchange. The State of Oregon and the United States Government assume no liability of its contents or use thereof. The contents of this report reflect the view of the authors who are solely responsible for the facts and accuracy of the material presented. The contents do not necessarily reflect the official views of the Oregon Department of Transportation or the United States Department of Transportation. The State of Oregon and the United States Government do not endorse products of manufacturers. Trademarks or manufacturers’ names appear herein only because they are considered essential to the object of this document. This report does not constitute a standard, specification, or regulation. iii iv REGIONAL PRECIPITATION-FREQUENCY ANALYSIS AND SPATIAL MAPPING OF 24-HOUR PRECIPITATION FOR OREGON Final Report TABLE OF CONTENTS EXECUTIVE SUMMARY ........................................................................................................ IX 1.0 OVERVIEW...........................................................................................................................1 2.0 STUDY AREA........................................................................................................................3 2.1 CLIMATIC AND METEOROLOGIC CHARACTERISTICS OF STUDY AREA ..................................................................................................................................3 2.1.1 Annual Precipitation....................................................................................................3 2.1.2 Weather Systems and Sources of Atmospheric Moisture ...........................................3 3.0 DATA SOURCES ..................................................................................................................7 3.1 PRECIPITATION GAGE TYPES, METHODS OF MEASUREMENT AND REPORTING.......................................................................................................................7 3.2 NUMBER OF GAGES AND GAGE TYPES .....................................................................8 4.0 DATA SCREENING AND QUALITY CHECKING .......................................................11 4.1 STATIONARITY AND SERIAL INDEPENDENCE ......................................................11 5.0 REGIONAL FREQUENCY ANALYSIS METHODOLOGY ........................................13 5.1 DESCRIPTION OF CLIMATIC/GEOGRAPHIC REGIONS..........................................13 5.2 CLIMATIC REGIONS FOR WESTERN OREGON STUDY AREA..............................16 Region 5 - Coastal Lowlands.................................................................................................16 Region 151 - Coastal Mountains West ..................................................................................16 Region 142 - Coastal Mountains East....................................................................................17