History of Flash flood in Timeline

Flash floods are rapid inundations of low-lying areas, characterized by a swift onset (less than six hours between rainfall and flooding). They are typically triggered by intense rainfall from severe thunderstorms, hurricanes, or tropical storms, as well as melting ice and snow. Catastrophic events like the collapse of natural ice or debris dams, or man-made structures such as the Johnstown Flood of 1889, can also cause flash floods.

2005: U.S. National Weather Service report on flood fatalities

In 2005, the U.S. National Weather Service reported that, based on a 30-year national average, floods caused more yearly deaths (127 on average) than lightning (73), tornadoes (65), or hurricanes (16).

2006: Analysis of flash floods in the United States begins

Beginning in 2006, analysis of flash floods in the United States shows that injuries and fatalities are most likely in small, rural catchments, the shortest events are the most dangerous, hazards are greatest after nightfall, and a high fraction of injuries and fatalities involve vehicles.

2012: Analysis of flash floods in the United States continues

Through 2012, analysis of flash floods in the United States shows that injuries and fatalities are most likely in small, rural catchments, the shortest events are the most dangerous, hazards are greatest after nightfall, and a high fraction of injuries and fatalities involve vehicles.

September 2015: Cloudburst in southern Utah leads to flash flood fatalities

In September 2015, a cloudburst in southern Utah resulted in 20 flash flood fatalities, with seven occurring in Zion National Park when hikers were trapped in a slot canyon.

2020: Impact severity scale proposed for flash floods

In 2020, an impact severity scale is proposed, providing a coherent overview of flash flood effects by classifying impact types and severity, and mapping their spatial extent across the floodplain. The scale classifies impacts into four categories: impacts on the built environment, impacts on man-made mobile objects, impacts on the natural environment, and impacts on the human population. It was proposed as a tool for prevention planning, offering insights on future impacts.