Iowa Real-Time Flood Forecasting System

The Iowa Flood Center (IFC) established in 2009 following the record floods of 2008 has developed a real-time flood forecasting system for the people of Iowa. The system complements the operational forecasting routinely issued by the National Weather Service through the River Forecast Centers and the local offices. The system is based on sound scientific principles of flood genesis and spatial organization and includes many technological advances. The core of the system is a continuous rainfall-runoff model that is based on landscape decomposition into hillslops and channel links. The decomposition follows the high-resolution airborne lidar-based Digital Elevation Model terrain analysis resulting in spatial resolution on the order of 0.01 km². Rainfall conversion of runoff is modeled as a continuo2us representation of empirical data better known in its integral version as Curve Number method. Channel routing is based on a non-linear representation of water velocity that accounts for the discharge amount as well as the upstream drainage area. Mathematically the model represents a large system of ordinary differential equations organized following river network topology. The IFC has developed a highly efficient numerical solver of the system suitable for High Performance Computing architecture. The solver allows the IFC to update its forecasts every 15 minutes for over 2000 forecast points that include over 1000 communities in Iowa. The input to the system comes from an in-house developed radar-rainfall algorithm that maps rainfall every five minutes with spatial resolution of about 0.25 km². The algorithm uses Level II radar reflectivity and other polarimetric data from the WSR-88DP radar network operated by the federal agencies. A unique feature of the algorithm is its advection correction method that improves accuracy of rainfall accumulations. The system is complemented by a large number of flood inundation maps and real-time river stage data from over 200 IFC “bridge sensors.” All information that the system generates is communicated to the general public through the Iowa Flood Information System, a browser based comprehensive and interactive platform.