Multi-scale statistical properties of rainfall in flash flood producing storms

The overall goal of the research is to improve operational flood forecasting on rapid runoff response watersheds in the Midwest for summer convective rainfall. The Driftless Area of southeast Minnesota, southwest Wisconsin, northwest Illinois, and northeast Iowa has been plagued in the past decade by record breaking floods including both flash floods and multi-day events. This area, along with the metro area and suburbs of Minneapolis/St. Paul were recently hit hard again by torrential rains and frequent flash flooding in the summer of 2014. In this presentation, the multi-scaling behavior of rainfall in this region will be explored to provide better understanding of the storms responsible for the quick response flood events. Focus will initially be placed on summer convective rainfall over the most problematic watersheds for flood forecasting in the North Central River Forecast Center (NCRFC) region. High resolution rainfall data from the Chanhassen, MN and La Crosse, WI radars will be used to quantify scaling behavior and organization of rainfall events. A cascade-based approach (described in Nykanen and Harris, 2003 and Nykanen, 2008) will be used to characterize the multi-scale statistical properties of the rainfall. Trends in development and dissipation of scaling properties of rainfall will be compared between flash flood producing storms and those that were non-flooding rainfall events. The objective is to better understand the scaling behavior of flash flood producing storms and explore if the flash flood potential can be detected from the multi-scaling properties of a developing storm. Scaling behavior between verified flash flood warned storms and false-alarm events will be compared for storms that elicited flash flood warnings. Influences of season, type of storms and rainfall patterns will also be explored.