The 1999 Flood of the Century: Extraordinary Hydrometeorological Event or Human-Induced Catastrophe?
Lecce, Scott A.; Kotecki, Erica S.
In 1999 the effects of Floyd, Dennis, and Irene caused unprecedented flooding, but was this a natural event or a human disaster? The researchers examined photographs of the effects of Hurricane Floyd and some other floods to compare flood stage. They also looked at drainage basins and census data to examine land use changes and how they have affected the drainage basins. Rainfall data at 21 stations were collected during Hurricane Floyd. Hurricane Dennis, which dumped 10–20 inches of rainfall in the Greenville area, saturated the soils, but did not cause major flooding. The three-week period including Hurricanes Dennis and Floyd was as much as 85% of annual rainfall. At these stations, there were 200- and 500-year recurrence intervals, which means this was an extreme event. Using parametric and non-parametric statistics they find a significant trend in annual mean discharge and flow, but not an association with human activities. There was no trend through time. In comparison to Mississippi River flooding, they found that floods are self-similar events and recurrence intervals are subject to a large amount of uncertainty. The largest events drown out human impacts since there is limited storage capacity of wetlands. During a period of rapid urbanization, there was little change in the stream flow at the scale of watersheds. Extreme precipitation plus the sequencing of storms means that there was not a difference due to human land use issues.