Forecasters and community leaders should look to the soil when deciding how to respond to the remnants of tropical storms moving through Illinois. Wetter soils will mean higher flood risks when the rains begin.
The connection likely comes as no surprise to those who work with weather and stream flow data—when soils reach their water-retention capacity, stormwater has little where else to go than into nearby waterways.
But understanding the strength of this connection, says meteorologist David Changnon, could help communities prepare for the often severe impacts of tropical storms.
Changnon, along with Northern Illinois University PhD student Alex Haberlie, compared precipitation data from 26 tropical storms with stream flow monitoring results in nine watersheds throughout the state.
They discovered that tropical systems temporarily increased the volume of water moving through streams by an average of 866 percent, with larger surges occurring in wet years. And the relatively large size of the storms meant that different regions experienced similar water level rises together.
“Tropical storms move slowly, and we are able to predict the amount of rainfall they will bring with higher accuracy than more localized systems,” said Changnon. “Forecasters can take advantage of this lead time to determine whether the storm is likely to trigger a flood.”
Illinois Water 2016
Photo: Flooding / Clark Maxwell / CC BY-NC-ND 2.0