Observed Trends in Extreme Precipitation: Illinois and Beyond

During a lifetime of work in hydrometeorology, Stan Changnon explored virtually every aspect of extreme precipitation in Illinois. Over time he extended this work to the regional and national scales. By the early 1980s, he had documented upward trends in extreme precipitation in Illinois, one of the first studies to find this just-emerging climate feature and putting him in the vanguard of numerous investigators who have found similar upward trends over much of the U.S. His studies of individual extreme events were many, including the 1993 Mississippi River flood and the July 1996 record-breaking event in northeast Illinois. I was privileged to join him on many of these studies during the latter portion of his career. In this talk, I will present some of the highlights of his extreme precipitation work. I will also present the latest regional analyses of U.S. trends in extreme precipitation. This analysis was performed in support of the development of the Third National Climate Assessment (NCA3) report. This analysis was organized around an 8-region breakdown of the U.S. The updated analysis indicates that trends are upward and statistically significant in five of the eight regions, mostly in the eastern half of the U.S. and Alaska. The pattern of trends in extremes is similar to long-term trends in mean annual precipitation. There is some correlation with trends in temperature-related extremes. In particular, increases in the number of heat waves and the length of the freeze-free season are largest in the western U.S. where trends in extreme precipitation are the smallest.