Floating a flood theory

hydrologic processes well enough because it changes with spatial scales,” said Gupta.

That’s shifting. Using flood data from the Iowa River and Cedar basins, and an experimental basin in Mississippi, Gupta and his colleagues have discovered a remarkable property: stream networks and floods are mutually related through self-similarity. As a result, scientists can extrapolate findings from a small study area to a much larger one; relationships between stream network and flooding remain similar and can be quantified and predicted.

“This gives us a foundation for extending our theories of flooding to ungauged catchments, where little data are available,” said Gupta.

Gupta is now applying his theory to the Whitewater Basin in western Kansas. Using the watershed as a natural laboratory, he and his collaborative research team are testing relationships between rainfall intensities, estimated from radar and rain gauge data, and physical characteristics of the basin. They’ve selected 12 stream gauging sites, representing watersheds ranging from a few square kilometers to several hundred.

Eventually, the researchers hope to generalize the geophysical theory from describing individual flooding events to predicting annual flood statistics. They also hope to learn how the hydrology, landscape, and ecology of Whitewater respond to changes in climate, agriculture, and residential development.

“The fundamental issue is whether we can generalize what we see at Whitewater to other watersheds,” said Gupta. “Success on this front would break new ground in flood prediction.” The End

Vijay Gupta

The American Geophysical Union awarded Vijay Gupta the prestigious 2008 Robert E. Horton Medal for his influential research in hydrology.

Gupta’s motivation is to improve real-time flood prediction, which is more art than science. Today’s forecast models typically rely on sparse precipitation data, and predictions are often compromised by a poor understanding of the hydrologic processes that govern rainfall and streamflow generation. “We still don’t understand the spatial variability in these

When water topped the Upper Mississippi’s banks in June 2008, more than 30,000 people were evacuated from Iowa City and Cedar Rapids, Iowa. The soaked cities and surrounding communities suffered more than $2 billion in damages. Today, recovery efforts are ongoing.

The catastrophic event offered a rare opportunity to test a nonlinear geophysical theory of floods, 20 years in the making. Spearheaded by CIRES Fellow Vijay Gupta, also a professor of civil and environmental engineering, the theory links spatial-temporal statistics of rainfall, streamflow, and flooding with physical watershed and channel network characteristics over spatial scales ranging from small tributary watersheds to large basins. According to Gupta, the theory seeks to resolve questions such as those involving the relationship between a watershed’s topography, the geometry of its river network, and spatial statistical streamflow variation.