The Nature of Extreme Rainfall and Hydrologic Extremes: Perspectives from the Past 100 Years (Part I) (Core Science Keynote) (Invited Presentation) (Centennial)

The Miami Conservancy was formed shortly before the American Meteorological Society with the goal of protecting the Miami River basin of Ohio from flooding. Innovations from the Miami Conservancy, which was created in response to the Great Flood of March 1913, shaped important aspects of hydrometeorology over the next century. Questions that focused initiatives for flood control in the early decades of the 20^th century included: how hard can it rain; are extreme floods simply the product of extreme rainfall; how does it rain hard? A central idea, directly linked to the first question, was that rainfall extremes and the resulting flood peaks are bounded. A second idea dealt with the “primary role of meteorology in flood flow estimation”, the title of Merrill Bernard’s 1944 paper in Transaction of the American Society of Civil Engineers. In this view, extreme floods are not simply the result of extreme rainfall, but nearly so. These ideas provided the foundations for Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF), principal tools used for engineering design during the period of peak dam building in the US during the middle decades of the 20^th century. Measurements, modeling and theory contributed to developments in hydrometeorology, but measurements occupied a central position in hydrometeorology until the latter decades of the 20^th century. Efforts to understand how it rains hard lagged behind empirical characterizations of the upper tail of rainfall and flood peaks during the 20^th century. Problems associated with extreme rainfall and flooding in mountainous terrain, coastal regions and urban environments place greater weight on understanding how it rains hard. The same holds for assessing the potential for increasing frequency of extreme rain rates in a warming climate. During the past several decades, advances in measurements (especially through weather radar and satellite sensors), and modeling (as reflected in marked advances in forecasting heavy rainfall and flooding) have contributed to positive steps in addressing how hard it can rain, how it rains hard and how land surface properties combine with rainfall to produce extreme floods.