Bulletin 71 (MCC Research Report 92-03) RAINFALL FREQUENCY ATLAS OF THE MIDWEST by Floyd A. Huff and James R. Angel Midwestern Climate Center Climate Analysis Center National Weather Service National Oceanic and Atmospheric Administration and Illinois State Water Survey A Division of the Illinois Department of Energy and Natural Resources 1992 Bulletin 71 (MCC Research Report 92-03) RAINFALL FREQUENCY ATLAS OF THE MIDWEST by Floyd A. Huff and James R. Angel Title: Rainfall Frequency Atlas of the Midwest. Abstract: This report presents the results and methodology of an intense study of rainfall frequency relationships throughout the Midwest (Illinois, Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, Ohio, and Wisconsin). Using primarily 275 long-term daily reporting stations from the National Weather Service (NWS) cooperative network supplemented by 134 daily reporting stations with shatter records, rainfall amounts have been determined for recurrence intervals from 2 months to 100 years and for durations of 5 minutes to 10 days. The results are presented as maps and as climate division averages in tabular form. Several special raingage networks were used to develop relationships between amounts for 24 hours and less. This report also examines the time distributions of heavy rainfall over time, and other storm characteristics such as storm orientation and movement. The assumption of spatially independent observations between stations is also discussed. Reference: Huff, Floyd A., and James R. Angel. Rainfall Frequency Atlas of the Midwest. Illinois State Water Survey, Champaign, Bulletin 71, 1992. Indexing Terms: Climatology, heavy rainfall, hydroclimatology, hydrometeorology, Midwest, extreme value distributions, climate change. The Midwestern Climate Center (MCC) is funded by a grant from the Climate Analysis Center, National Weather Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce STATE OF ILLINOIS HON. JIM EDGAR, Governor DEPARTMENT OF ENERGY AND NATURAL RESOURCES John S. Moore, B.S., Director BOARD OF NATURAL RESOURCES AND CONSERVATlON John S. Moore, B.S., Chair Robert H. Benton, B.S.C.E., Engineering Donna M. Jurdy, Ph.D., Geology H.S. Gutowsky, Ph.D., Chemistry Roy L. Taylor, Ph.D., Plant Biology Robert L. Metcalf, Ph.D., Biology W.R. “Reg” Gomes, Ph.D. University of Illinois John H. Yopp, Ph.D. Southern Illinois University STATE WATER SURVEY DIVISION JOHN T. O’CONNOR, Chief 2204 GRIFFITH DRIVE CHAMPAIGN, ILLINOIS 61820-7495 1992 ISSN 0360-9804 Funds derived from grants and contracts administered by the University of Illinois were used to produce this report. This report was printed on recycled and recyclable paper. Printed by authority of the State of Illinois (12-92-1.6M) CONTENTS Page Introduction .................................................................................................................................. 1 Storms in the Midwest ........................................................................................................ 1 Rationale for the Study ....................................................................................................... 1 Organization of the Report .................................................................................................. 2 Basic Considerations........................................................................................................... 2 Pilot Study ......................................................................................................................... 3 Information Accumulated for Each State................................................................. 3 Acknowledgments ............................................................................................................. 3 Part 1. Analyses ............................................................................................................................. 5 1. Data and Analytical Approach .................................................................................................... 5 2. Statistical Methods..................................................................................................................... 7 Background........................................................................................................................ 7 Analytical Method Employed in the Nine-State Study........................................................... 7 Comparison of Huff-Angel, L-moments, and Maximum Likelihood Methods' Fitting Procedures for Selected States .................................................................................. 8 Maximum Likelihood Method ................................................................................. 8 L-moments Method................................................................................................. 8 L-moments Regions ................................................................................................ 8 Results ................................................................................................................... 9 Indiana ....................................................................................................... 9 Minnesota................................................................................................... 10 3. Frequency Distributions of Heavy Rainfall Events ....................................................................... 18 Point Rainfall Frequency Distributions................................................................................. 18 Areal Mean Frequency Distributions.................................................................................... 18 4. Time Distributions of Rainfall in Heavy Storms........................................................................... 20 Method and Results of Analysis........................................................................................... 20 Application of Results......................................................................................................... 20 Using Results in Structural Design Problems: Case Studies ................................................... 20 Case One................................................................................................................ 20 Case Two ............................................................................................................... 20 Case Three ............................................................................................................. 20 5. Seasonal Distributions of Heavy Rainfall..................................................................................... 25 Background........................................................................................................................ 25 Analysis and Results........................................................................................................... 25 Seasonal Precipitation ............................................................................................. 25 Seasonal Distribution of Heavy Rainstorms ............................................................. 25 Rainfall Frequencies by Season................................................................................ 25 Summary ........................................................................................................................... 28 CONTENTS (Concluded) 6. Fluctuations in Frequency Distributions of Heavy Rainstorms in the Midwest ................................ 32 Background............................................................................................................................. 32 Analytical Approach and Results ............................................................................................ 32 Illinois ........................................................................................................................ 32 The Midwest .............................................................................................................. 33 Summary and Conclusions ..................................................................................................... 34 7. Spatial Characteristics of Heavy Rainstorms in the Midwest ........................................................... 36 Relation Between Point and Areal Mean Rainfall Frequency .................................................. 36 Storm Shape ........................................................................................................................... 36 Storm Orientation.................................................................................................................... 37 Storm Movement .................................................................................................................... 37 8. Independence of Extreme Rainfall Events ....................................................................................... 38 Examples of Outstanding Storms ............................................................................................ 38 Additional Analyses ............................................................................................................... 41 Summary ................................................................................................................................44 9. Variability within Climatic Sections................................................................................................ 45 10.