Roadway floods and their associated weather-related conditions: New insights using CARS 511 data for state and federal highways in Nebraska, USA

This study examined roadway flooding event data provided by the Nebraska Department of Transportation via the Condition Acquisition Reporting System (CARS) 511 archive (2016-2021). With these data, a novel analysis was completed to further the understanding of where, when, and why (meteorologically) roadway flooding occurs on Nebraska state and federal highways. In the study period, 298 roadway floods occurred, with an annual median of 16 per year. There was a greater risk for roadway floods to transpire more frequently in eastern Nebraska, which was attributed to the spatial climatology of heavy rainfall and the higher density of roadways and rivers. Consequently, this increases the exposure and vulnerability of the highway system across the eastern portion of the state. Further, precursor soil moisture and river conditions proved to be critical initiators of roadway floods, as precipitation totals prior to each flood only averaged at 40 mm, while precursor Palmer Hydrological Drought Index values for 75% of events were above 4.0 and river levels were 200 cm above its daily medians. Overall, the complexities of these roadway flooding events are challenging for proactively forecasting as opposed to reacting to the situation. With the top roadway flooding locations identified along with the weather-related causes, further investigation of roadway flooding hotspots across the state needs to take place for mitigation and resiliency in a changing climate. The methods of this research can be used across other states and by other agencies to analyze and increase the resilience of their respective roadway networks.