CLIMATE CHANGE INFLUENCE ON HISTORICAL FLOOD VARIABILITY IN OZARK HIGHLAND RIVERS A Masters’ Thesis Presented to The Graduate College of Missouri State University In Partial Fulfillment Of the Requirements for the Degree Master of Science, Geospatial Science with Physical Geography By Andrew Thomas Foreman August 2014 i Copyright 2014 by Andrew Thomas Foreman ii CLIMATE CHANGE INFLUENCE ON HISTORICAL FLOOD VARIABILITY IN OZARK HIGHLAND RIVERS Geography, Geology, and Planning Missouri State University, August 2014 Master of Science Andrew Thomas Foreman ABSTRACT Climate change influence on the hydrology and ecology of Midwestern Rivers is poorly understood. Flood frequency analysis is used to interpret the historical variability of, and recent trends in, flood magnitudes in Ozark Highland Rivers. Flood frequency distributions for the annual maximum series were calculated over 30 year periods at 5 year intervals from 1922 to 2012 to examine temporal trends of flood magnitudes ranging from the 1.5- to 100-year recurrence intervals. Discharges of the 2-year flood have increased by an average of 30% over the past 30 years, in eleven of the twelve studied rivers. Eight of the studied rivers have 25-year flood discharges that are currently greater than the long-term 50-year flood magnitude. Discharges of the 100-year flood have increased by an average of 39% for eleven of the studied rivers. Urban area % seems to play a role in the observed increases in high frequency floods, but has little to no effect on moderate/low frequency floods changes. A potential climate-related latitudinal control on high frequency flood discharges exists, though more study is needed. Recent increases in floods are more prominent in basins > 2,000 km2. This finding provides a potential drainage area threshold under which floods have not increased significantly over recent time. USGS regression equations under predict 100-year flood discharges for ten of the twelve studied rivers. Recent increases in flood discharges in the Ozarks are likely linked to increased precipitation extremes observed across the Midwest as a result of anthropogenic climate change. KEYWORDS: Ozarks, flood, climate, rivers, change, time This abstract is approved as to form and content Dr. Robert Pavlowsky Chairperson, Advisory Committee Missouri State University iii CLIMATE CHANGE INFLUENCE ON HISTORICAL FLOOD VARIABILITY IN OZARK HIGHLAND RIVERS By Andrew Thomas Foreman A Masters Thesis Submitted to the Graduate College Of Missouri State University In Partial Fulfillment of the Requirements For the Degree of Master of Science, Geospatial Science with Physical Geography August 2014 Approved: ______ ______ ______ Dr. Robert Pavlowsky ______ ______ ______ Dr. Douglas Gouzie ______ ______ ______ Dr. Jun Luo ________________________________________________ Thomas Tomasi, PhD, Associate Dean Graduate College iv ACKNOWLEDGEMENTS I would like to thank the following people for their support during the course of my graduate studies. My graditude for Dr. Robert Pavlowsky knows no bounds, for his invaluable knowledge about Missouri hydrology and continuous help throughout my entire graduate college experience. Dr. Daoust was always available and offering help, and I thank him too. I’d like to thank Dr. Luo and Dr. Gouzie for serving on my committee throughout my graduate studies. Marc Owen, I thank for allowing me to annoy him with requests to use his computer when none others carried the required software. For her previous research and attention to detail, I would like to thank Megan Harrington. I would also like to give thanks to the university-based entities that gave financial, emotional, and educational support throughout my graduate studies at Missouri State University including the Ozarks Environmental and Water Resources Institute (OEWRI), the Department of Geography, Geology, and Planning, and the Graduate College. I can’t thank Carol and Kevin Foreman (Mum and Dad) enough for their undying support and love that got me where I am today. Finally, I want to thank Hillary Kummer, for her unerring support and boundless love that got me through the tough times with a smile on my face and the will to keep striving for my best. v TABLE OF CONTENTS Introduction ..........................................................................................................................1 Purpose and objectives .............................................................................................4 Background ..........................................................................................................................5 Controls on flooding ................................................................................................5 Climate .........................................................................................................5 Land use .......................................................................................................7 Geology ........................................................................................................8 Midwest flood trends ...............................................................................................9 Flood frequency analysis .......................................................................................11 Study Area .........................................................................................................................13 Geology and soils ....................................................................................................13 Vegetation and land use ..........................................................................................18 Climate ....................................................................................................................20 Methods..............................................................................................................................24 Gage selection .........................................................................................................24 Data collection ........................................................................................................24 Watershed characteristics ........................................................................................25 Flood frequency analysis ........................................................................................26 High frequency floods................................................................................26 Moderate frequency floods ........................................................................27 Low frequency floods ................................................................................27 USGS 100-year flood regression equation .............................................................28 Units ........................................................................................................................29 Results and Discussion .....................................................................................................30 Annual maximum discharge trends ........................................................................30 90-year trends.............................................................................................30 Flood record sensitivity..............................................................................38 Peak discharge - drainage area relationships ..........................................................42 2-year flood ....................................................................................42 Mean >10-yr flood ........................................................................44 Changes in variability over time ............................................................................46 Flood Frequency Analysis ......................................................................................48 Overlapping magnitude-frequency analysis (OM-FA) trends. ..................48 High frequency floods....................................................................53 Moderate frequency floods ............................................................55 Low frequency floods ....................................................................55 Recent Trends ...........................................................................................56 High frequency floods....................................................................57 Moderate frequency floods ............................................................58 vi Low frequency floods ...................................................................59 Flood record inflection ............................................................................................62 Correlation analysis ................................................................................................63 USGS discharge estimate comparison ....................................................................69 Implications.............................................................................................................72 Land use influence on Ozark Highland floods .......................................................73 Climate change influence on Ozark Highland floods .............................................75 Conclusions ........................................................................................................................77 Literature Cited ..................................................................................................................82