Small increases in rainfall could cause big problems for road networks

By Rayla Bellis
There is a lot we still don’t know about how climate change will affect transportation networks and how to make infrastructure more resilient, but new research sheds some light on these questions. A model developed to study the impacts of floods on road networks indicates that even small, localized increases in rainfall could cause widespread disruptions and road outages.
The model combines road network and topography data, integrating a traditional network science approach—to predict how disruptions affect transportation systems—with environmental models predicting how topography influences flooding. Altitude and the flow of water over land add complexity to network modeling. Heavy rainfall can be locally destructive, but can also have much farther-reaching impacts thanks to the spatial dispersion of floodwaters through rivers and the altitude of the roads themselves.
In particular, the model indicates that there are tipping points in each geographic area above which localized rainfall could cause major failures to the road network—fully disconnecting sections from each other—because flooding has knocked out all of the specific critical routes or intersections. For example, in Florida, the researchers found that an increase from 30 millimeters to 35 millimeters of rainfall knocked out 50 percent of the road network. In New York, runoff greater than 45 millimeters isolated the northeastern part of the state from the interior of the United States.
The research also found that certain roads and intersections that would not typically be recognized as critical connections based on the road network alone become the “last line of defense” in a flood scenario because they maintain connections between sections of the network when all other connections have flooded. For example, roads and intersections that are close to rivers but at higher altitudes often become more crucial. The study team noted that these intersections should therefore be prioritized when developing strategies of disaster prevention.
A network scientist at Rensselaer Polytechnic Institute teamed up with environmental scientists at Beijing Normal University and a physicist at Boston University to develop the model. The researchers validated it by comparing predicted results with observed road outages in Houston and Southeast Texas caused by Hurricane Harvey. The model predicted 90.6 percent of reported road closures and 94.1 percent of reported flooded streets.
Rayla Bellis is a Program Manager at SSTI.