Projected Changes in Flood Peak Discharge Across Iowa: A Flood Frequency Perspective

Numerous modeling studies point to an intensification of the hydrological cycle under projected climate warming, with increasing frequency of extreme events, including heavy rainfall and flooding. Recently, the occurrence of extreme flooding has becoming the norm rather than the exception, with the 2008 Eastern Iowa flood representing the “poster child” for this catastrophic situation: during this event, for instance, the eastern half of our state experienced the closure of a number of roads, including Interstate 80. So, what would projected changes in flooding mean for the Iowa Department of Transportation (IDOT) and the bridges and structures that constitute Iowa’s highway system? How resilient are these highway structures to different climate warming scenarios? Addressing these questions requires flood frequency analysis. The current methodology relies on the guidelines by Bulletin 17C. However, issues related to regionalization of at-site estimates as well as accounting for the projected changes in the climate system have received little attention despite the potentially large impacts, including to the IDOT’s infrastructure. The proposed approach builds on methodologies and datasets with which the research team have extensive experience. Specifically, the proposed work focuses on the examination of the projected changes in flooding across Iowa using two complementary approaches: one based on the hydrologic model developed by the Iowa Flood Center (IFC), and one based on the statistical relationship between flooding and climate drivers. The focus will be on high-resolution and downscaled outputs from CMIP5 (Fifth Coupled Model Intercomparison Project) and CMIP6 (Sixth Coupled Model Intercomparison Project), and different scenarios.