November 6, 2009 | NCAR postdoctoral researcher Isabelle Ruin studies how people and organizations respond to extreme weather events—in particular, flash floods. Flash floods are already on average the leading cause of weather-related fatalities in the United States and second most common worldwide. Scientists expect that floods will become more widespread and threatening as the planet heats and rainfall intensifies due to climate change.

In a study published in July 2008 in the Journal of Hydrology, Ruin investigated the hydrometeorological factors that led to 23 deaths during a flood in France's Gard region in 2002, with an eye toward how human vulnerability relates to the size of the catchment, or drainage basin, during a flash flood. The study found that, as the authors expected, small catchments with shorter response times caused more fatalities.

Ruin and NCAR scientist Olga Wilhelmi recently teamed with Daniel Pollak, a protégé in UCAR's Significant Opportunities in Atmospheric Research and Science (SOARS) program, to apply the study's methodology to a 2008 flash flood in Missouri that led to two fatalities and 20 water rescues.

Pollak used GIS to create a spatial and temporal analysis of incidents that occurred during the flash flood and compared this with factors such as rainfall data and catchment size. His results showed that, similar to the Gard study, very small catchments (less than 50 square kilometers, or about 20 square miles) pose the largest hazards, particularly with regard to travel as they tend to flood roads easily.

With the goal of improving flash flood warnings, Ruin and Wilhelmi are taking Pollak's case study a step further by working with National Weather Service forecasters in Springfield, Missouri, to statistically analyze about one thousand flash flood incident reports from 2007 and 2008 in relation to catchment size.

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