What is a key characteristic of flash floods?

Flash floods are characterized by their sudden onset, often developing within minutes to hours of intense rainfall or other circumstances, such as dam breaks or rapid snowmelt. This rapid emergence poses significant risks as they can occur with little to no warning, making them particularly dangerous. The high potential for loss of life and property damage contributes to their description as often deadly events.

The other options do not accurately describe the nature of flash floods. While they may be confined to specific regions, including lowland areas in some instances, this is not a defining trait. Flash floods can indeed occur in a variety of terrains. In contrast to the gradual inundation described in the fourth option regarding groundwater levels, flash floods arise quickly due to intense surface runoff rather than a slow increase in water table levels. The defining factor is the immediate danger posed by the swift and unpredictable nature of these floods, which can catch people off guard and lead to tragic consequences.